Article: 98094 of rec.radio.amateur.homebrew From: aadu.adok@gmail.com Subject: could VFO frequency be below IF ? Date: 19 Jul 2006 00:54:44 -0700 Message-ID: <1153295684.841238.155880@i3g2000cwc.googlegroups.com> hi, I'm experimenting with my superhet. My IF is 8mhz (cause I have 8 mhz crystals for IF filter). I first experimented on 40m. VFO was 15mhz. At design time I'm using 3 meters long wire as an "antenna" (and I'm sitting in my basement). I heard different european stations (EA5FKX, RW6XE, UR4GI etc) which are several thousand km-s away. Pretty amazing for such "antenna"! So I decided to go for 20m band. I had an option to set my VFO either to 6mhz or 22mhz. I first went with 6mhz. But for my disappointment I heard nothing but the band noise. So I'm confused now - is it because the short "antenna" or am I wrong thinking that VFO 6mhz + IF 8mhz should give me 14mhz? any ideas? Article: 98095 of rec.radio.amateur.homebrew From: MAc Subject: Re: could VFO frequency be below IF ? Date: Wed, 19 Jul 2006 10:39:49 +0200 Message-ID: References: <1153295684.841238.155880@i3g2000cwc.googlegroups.com> Yes. It was often used in two band trx - with 9MHz IF and 5-5,5MHz VFO. result was 80m and 20m without VFO switching. MAc Article: 98096 of rec.radio.amateur.homebrew From: "AndyS" Subject: Re: What is a wire antenna's impedance? -followup Date: 19 Jul 2006 03:00:50 -0700 Message-ID: <1153303250.437820.161760@75g2000cwc.googlegroups.com> References: <7T9tg.15155$Wh7.1326@trnddc07> John - KD5YI wrote: > Where is the counterpoise on a handheld transceiver? I believe it is the > body of the transceiver, the hand, arm, and body of the operator, and the earth. > ****** Yes. If the case is conductive. Even if the case is metal , and not connected to the internal "ground" , it becomes part of the counterpoise by capacitance. Of course, the hand is conductive, etc..... So, I tried to make > some measurements to show how much variation there can be with wire antennas > and to underscore the fact that there is no way anyone can predict what a > wire antenna's impedance will be on the objects the OP referred to under the > myriad of conditions possible. > \ **** And you did that very effectively. I didn't realize that you were trying to show the significant variations, and thought you were wondering why the readings were so different. Sorry,.... I just didn't get your intent.... I would have liked to see what the piece of wire did with a nice ground plane, tho, to see what the design baseline would have been.... In other words, a piece of wire looks like, say 32 ohms over a ground plane, but when all the variables such as shape, no ground plane, people, nearby objects, etc come into play, it goes from hell to high water..... I'm glad to see someone actually doing the experiments, rather than just quoting a bunch of " E to the J Beta pitchforks" and letting it go at that....... :>))))) Andy W4OAH > Cheers, > John Article: 98097 of rec.radio.amateur.homebrew Date: Wed, 19 Jul 2006 11:29:48 +0100 From: Highland Ham Subject: Re: What is a wire antenna's impedance? -followup References: <7T9tg.15155$Wh7.1326@trnddc07> <1153256978.081184.264550@p79g2000cwp.googlegroups.com> Message-ID: <--2dnUFXZrQalCPZRVnytA@pipex.net> > My suggestion > is that you need a good counterpoise...... Maybe buy a sheet of > corrugated tin from Home Depot, mount the connector in the middle, > with the MFJ on one side and the antenna wire on the other.... You'll > find, I am certain, that your readings will be more consistent..... > > This is not a bad ground plane for 2 meters --- I have used one > with good results...... ========================== Alternatively you could use a ground plane of chicken wire mesh ,a bit easier to handle than a sheet of metal. Frank GM0CSZ / KN6WH Article: 98098 of rec.radio.amateur.homebrew From: "AndyS" Subject: Re: What is a wire antenna's impedance? -followup Date: 19 Jul 2006 06:05:21 -0700 Message-ID: <1153314321.570078.313180@b28g2000cwb.googlegroups.com> References: <7T9tg.15155$Wh7.1326@trnddc07> Highland Ham wrote: > ========================== > Alternatively you could use a ground plane of chicken wire mesh ,a bit > easier to handle than a sheet of metal. > > Frank GM0CSZ / KN6WH Andy comments: That's a good idea. I always seem to have some tin laying around and no chicken wire, but it would work well. Also hardware cloth -- that stuff with the little squares that is used a lot on rabbit cage bottoms..... In fact, they would both be good for corner reflectors, with a PVC frame... Or a large bowtie dipole to get broadband at VHF........ hmmmmmmmm. Thanks Frank, you have ALMOST inspired me to start another project........... maybe tomorrow :>))))) Andy W4OAH Article: 98099 of rec.radio.amateur.homebrew From: "AndyS" Subject: Re: could VFO frequency be below IF ? Date: 19 Jul 2006 06:39:25 -0700 Message-ID: <1153316365.225113.152100@m73g2000cwd.googlegroups.com> References: <1153295684.841238.155880@i3g2000cwc.googlegroups.com> aadu.adok@gmail.com wrote: > So I decided to go for 20m band. I had an option to set my VFO either > to 6mhz or 22mhz. I first went with 6mhz. But for my disappointment I > heard nothing but the band noise. > > So I'm confused now - is it because the short "antenna" or am I wrong > thinking that VFO 6mhz + IF 8mhz should give me 14mhz? > > any ideas? Andy writes: Sometimes 20m is deader than a doornail. Nothing.... Other times, the band is hopping....... Try it again, maybe at dawn or dusk..... If your system is working properly, you probly just caught 20m at the wrong time. ...... Kind of like catching the refrigerator in the middle of a defrost cycle when you put your beer in to get it cold ...... you just gotta wait .... :>)))) I would also suggest that you get a mixer chart and get familiar with how to choose LO and IF frequencies for minimum spurious responses. There is a mixer spur graph in Ref Data for Radio Engineers, and maybe in the ARRL handbook.. Also , Minickts labs puts out spur response charts for their popular mixers such as the SBL-1 and MD108 and it shows which of the spurs are worst and allows you to adjust your mixing frequencies accordingly. The selection of a good frequency scheme is the STARTING point for a receiver design. I know you are using stuff that you have on hand, as all of us have done, but if you get familiar with frequency management you will be able to account for the signals you hear but don't know why..... It's usually due to spurious mixer responses.... Here's a couple rules of thumb, if you have NO OTHER WAY to get the info you neet. 1) If the LO is either 9/10 of the received freq, ( or 1.1 times the received freq for top side injection,), most spurs are low response. 2) If the LO is near .25 , .50 or .75 the channel freq, spurs are really bad. 3) The image response is equal to the desired ---- use front end filtering. (assuming you don't use an image regect mixer) 4) The "half-IF" response 2LO+/-2RF = IF , is really bad, always..... Use front end filtering to get it down also... Example: RF 7mhz LO 15 mhz Half IF is 11 mhz Image is 23 mhz Those are just off the top of my head. The best deal is to pull out a mixer chart. Personally, I wrote a little BASIC program to go thru all the combinations up to the 10th harmonic and print out all the responses that occur in a bandpass I could specify... it's easy to do and gives you exact numbers......r .... but the mixer graph can get you in the ball park quickly....... Andy W4OAH Article: 98100 of rec.radio.amateur.homebrew From: Arthur Subject: Re: Newbie Question: PC Based Oscilloscopes Date: Wed, 19 Jul 2006 15:37:33 -0000 Message-ID: <12bskdt13nm3p2f@corp.supernews.com> References: <1153260845.004678.264980@p79g2000cwp.googlegroups.com> Timothy@tholtom.freeserve.co.uk wrote: > > I haven't touched RF test and measurement equipment for about 20 years. > Back then I used a standard 50MHz dual trace scope. I want to get > back into homebrewing, and was wondering whether anyone could advise me > on buying PC based 'scopes. Do they have the same "look and feel" as a > dedicated 'scope? > > There appear to be many such PC based scopes (e.g. Vellman), I was > wondering what homebrewers would advise, given the "average" budget > (not 10,000 Dollars + !!). Something with a pretty good Spectrum > Analyser built in? > > Or would I be better off going to Ebay and buying an old dual trace > scope for 100 Euros or so? > > Advice anyone? You might want to check how much RF your PC is leaking first. Also check to see if the software can be run directly off a CD without installing anything on your HD. My PC has enough to do already. I prefer a dedicated time-based oscilloscope. RF spectrum analyzers are expensive cupholders, nice to have but ... well, if someone gave one to me for free I wouldn't complain. Article: 98101 of rec.radio.amateur.homebrew From: Bill Turner Subject: Re: could VFO frequency be below IF ? Date: Wed, 19 Jul 2006 08:44:47 -0700 Message-ID: References: <1153295684.841238.155880@i3g2000cwc.googlegroups.com> ORIGINAL MESSAGE: On 19 Jul 2006 00:54:44 -0700, aadu.adok@gmail.com wrote: >So I decided to go for 20m band. I had an option to set my VFO either >to 6mhz or 22mhz. I first went with 6mhz. But for my disappointment I >heard nothing but the band noise. ------------ REPLY SEPARATOR ------------ That frequency combination will work fine. I once homebrewed a 40 meter SSB rig using a 9 MHz crystal IF filter and a 2 MHz oscillator and it worked fine. As a rule, the lower the oscillator frequency, the more stable it will be. Your 6 MHz will be far more stable than 22 MHz. Bill, W6WRT Article: 98102 of rec.radio.amateur.homebrew Date: Wed, 19 Jul 2006 09:52:13 -0700 From: Tim Wescott Subject: Re: could VFO frequency be below IF ? References: <1153295684.841238.155880@i3g2000cwc.googlegroups.com> Message-ID: aadu.adok@gmail.com wrote: > hi, > > I'm experimenting with my superhet. My IF is 8mhz (cause I have 8 mhz > crystals for IF filter). I first experimented on 40m. VFO was 15mhz. At > design time I'm using 3 meters long wire as an "antenna" (and I'm > sitting in my basement). I heard different european stations (EA5FKX, > RW6XE, UR4GI etc) which are several thousand km-s away. Pretty amazing > for such "antenna"! > > So I decided to go for 20m band. I had an option to set my VFO either > to 6mhz or 22mhz. I first went with 6mhz. But for my disappointment I > heard nothing but the band noise. > > So I'm confused now - is it because the short "antenna" or am I wrong > thinking that VFO 6mhz + IF 8mhz should give me 14mhz? > > any ideas? > What everyone else said, plus: Yes, a mixer should work on both sum and difference frequencies, so an LO that's lower than the IF is just fine for receiving a good strong signal. You leave yourself open to more spurious reception problems. When folks are talking about 'spurs' and 'mixer charts' they mean you need to watch out for funky combinations of harmonics of LO and RF signals mixing down to your IF -- having the LO frequency higher than the RF frequency tends to reduce this problem. You can do this by hand by assuming that you'll be mixing 6, 12, 18, 24, etc., with 14, 28, 42, etc., and seeing if any of the combinations boils down to an IF of 8. If they do you could have spurious mixing problems, particularly if they're not high harmonics. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html Article: 98103 of rec.radio.amateur.homebrew From: "Joel Kolstad" Subject: Re: What is a wire antenna's impedance? -followup Date: Wed, 19 Jul 2006 11:14:18 -0700 Message-ID: <12bstjoj1act014@corp.supernews.com> References: <7T9tg.15155$Wh7.1326@trnddc07> <1153256978.081184.264550@p79g2000cwp.googlegroups.com> <12bqlmvsdbhisb2@corp.supernews.com> <1153262499.873796.22260@h48g2000cwc.googlegroups.com> Hi Andy, "AndyS" wrote in message news:1153262499.873796.22260@h48g2000cwc.googlegroups.com... > Now, if the counterpoise was at infinity, the Efield must always be > zero, > since any voltage divided by infinity ( to give V/M) will be zero. If I take a charged sphere with 1V applied, the E field falls off as 1/R all the way out to infinity; it is only there that it's actually zero, yes? > If you know of an antenna that has no counterpoise for the "hot" > side to > work against, please post some information about it...... How about a half-wave antenna (end-fed zepp)? Assuming it's being fed by coax, would you suggest the counterpoise is the ring making up the shield of the coax right where the coax stops and the antenna starts? I would like to hear from someone like Roy as well, since I certainly am well outside of any areas of significant experience here. ---Joel Article: 98104 of rec.radio.amateur.homebrew From: "Joel Kolstad" Subject: Re: Newbie Question: PC Based Oscilloscopes Date: Wed, 19 Jul 2006 11:26:36 -0700 Message-ID: <12bsuaqddr37ma9@corp.supernews.com> References: <1153260845.004678.264980@p79g2000cwp.googlegroups.com> <1153263203.500013.191710@m73g2000cwd.googlegroups.com> "AndyS" wrote in message news:1153263203.500013.191710@m73g2000cwd.googlegroups.com... > I MUCH MUCH MUCH prefer the old fashioned analog scopes, tho, since > I can fiddle with it and don't have to worry about aliasing, sample > rates, etc. A *good* digitial scope will contain an anti-alias filter and sufficient smarts that you genereally shouldn't have to worry about these issues -- if you were to take a new Tektronix or Agilent DSO (or at least the "mid-grade" or higher "trim levels" -- the ones that show properly shaded waveforms to indicate how much time signals spend at various levels), I'm willing to bet you'd be just as happy as with your old analog scope. Not that there's anything wrong with the old analog scopes. :-) One of the main problems with inexpensive PC-based oscilloscopes is the fact that the specs are often considerably "low end" but often not presented in a way that makes this apparent. I honestly believe that some people think that hooking an analog signal directly to the input of, say, a 100Msps ADC somehow makes a "100MHz scope." :-( Here's a nice comparison from cleverscope -- people who do seem to know what they're doing -- that compares various PC-based scopes: http://www.cleverscope.com/resources/Cleverscope%20Comparison%20chart.pdf ---Joel Kolstad Article: 98105 of rec.radio.amateur.homebrew From: Bill Turner Subject: Re: Newbie Question: PC Based Oscilloscopes Date: Wed, 19 Jul 2006 12:25:09 -0700 Message-ID: References: <1153260845.004678.264980@p79g2000cwp.googlegroups.com> <1153263203.500013.191710@m73g2000cwd.googlegroups.com> ORIGINAL MESSAGE: On 18 Jul 2006 15:53:23 -0700, "AndyS" wrote: > I MUCH MUCH MUCH prefer the old fashioned analog scopes, tho, since >I can fiddle with it and don't have to worry about aliasing, sample >rates, etc. ------------ REPLY SEPARATOR ------------ Analog scopes are good when the human eye can perceive the trace adequately. Digital scopes are best with waveforms that are either too slow or too fast (and non-repetitive). Each has its place. Bill, W6WRT retired test technician, Tektronix 400-series portable digital scopes Article: 98106 of rec.radio.amateur.homebrew From: "Gregory D. MELLOTT" Subject: Re: toroid cores? References: Message-ID: Date: Wed, 19 Jul 2006 19:37:08 GMT Jamie wrote: > In , > Scott mentions: >>Well, I'm not sure about a lot of the questions you asked, so I would >>suggest waiting to hear from others for ideas or, in true hamming >>spirit, give it a go and see what happens :) >> >>I wish you good luck...it sounds like an interesting project! > > Thanks. > > Looks like I may have fried the FET. :-( > > No matter what I did, I simply could not get feedback. I hooked an LM368 audio > amp pretty much directly to the RF signal generator and I could vaguely hear it, > so... I'm thinking the reason it was working the way it did (with the "station" > comming in stronger as I tuned it) was simply the LM386 acting like a detector > in a TRF radio :-/ (The thing that confused me was, if I held an AM radio really > close to the coil, I DID get some interference, but I couldn't hear a squeal in > the speaker of my radio. > > I put it away for now, I do have another FET I could f^Htry, but.. I don't want to > damage it. > > I was thinking about removing the pot entirely and using a rotating "inner coil" > serve in it's place: > > +v ------> (tickler coil) ---> [D|G|S] ---> audio out > > (Basically using both sides of the FET) > > Hooking the tank circuit up to the gate, just as before but eliminate the > parts for controlling the tickler, sort of like this: > > <()> with < > being the tank coil and the () being a coil inside the <>'s > in such a way you could turn it, controlling the tickler by changing > it's angle. > > I've seen old regen radios that appear to do something like this, but constructing > a coil that can be turned (w/out changing the tank and input coil's value) look > tricky. A plastic ink pen could be the shaft for turning it, but keeping it > in the center w/out wobbling.. > > As the parts MUST come from garbage, precise values are hard to get. > > To remove them is a good thing. :-) > > Not today though.... > > Jamie Hi, My luck (quite some time ago) with FETs was not nice either. Someone may have to correct my, yet the only way I think one can get away with fiddling with the things the way most people construct, might be to use zener diodes between the gate and source and drain. Once its all together and apparently functioning one probably could remove them then with less worry about then getting a little static jolt and ruining the junction. Tubes are a lot more forgiving. Sincerely, Gregory D. MELLOTT Article: 98107 of rec.radio.amateur.homebrew From: "Mike Andrews" Subject: Re: toroid cores? Date: Wed, 19 Jul 2006 19:40:21 +0000 (UTC) Message-ID: References: Gregory D. MELLOTT wrote: > My luck (quite some time ago) with FETs was not nice either. Someone may have to > correct my, yet the only way I think one can get away with fiddling with the > things the way most people construct, might be to use zener diodes between the > gate and source and drain. Once its all together and apparently functioning one > probably could remove them then with less worry about then getting a little > static jolt and ruining the junction. Tubes are a lot more forgiving. With tube stuff, touching the wrong thing will kill you. With sand stuff, touching the wrong thing will kill it. -- Mike Andrews, W5EGO mikea@mikea.ath.cx Tired old sysadmin Article: 98108 of rec.radio.amateur.homebrew Date: Wed, 19 Jul 2006 20:42:06 +0100 From: Highland Ham Subject: Re: What is a wire antenna's impedance? -followup References: <7T9tg.15155$Wh7.1326@trnddc07> <1153256978.081184.264550@p79g2000cwp.googlegroups.com> <12bqlmvsdbhisb2@corp.supernews.com> <1153262499.873796.22260@h48g2000cwc.googlegroups.com> <12bstjoj1act014@corp.supernews.com> Message-ID: > How about a half-wave antenna (end-fed zepp)? Assuming it's being fed by > coax, would you suggest the counterpoise is the ring making up the shield of > the coax right where the coax stops and the antenna starts? =============================================== End fed Zepp antennas I have come across are fed with a balanced feeder. Frank GM0CSZ / KN6WH Article: 98109 of rec.radio.amateur.homebrew From: "AndyS" Subject: Re: What is a wire antenna's impedance? -followup Date: 19 Jul 2006 16:12:38 -0700 Message-ID: <1153350758.355083.197900@h48g2000cwc.googlegroups.com> References: <7T9tg.15155$Wh7.1326@trnddc07> Joel Kolstad wrote: > > If I take a charged sphere with 1V applied, the E field falls off as 1/R all > the way out to infinity; it is only there that it's actually zero, yes? > ***** One volt with respect to what other point ?? The RF generator which drives the antenna has TWO terminals. If one terminal is connected to the wire, or the sphere, the OTHER terminal must be connected to something else for the antenna to radiate. Hence, one terminal is connected to one side of the antenna, balanced or unbalanced, and the other terminal is connected to either the other side of a balanced antenna, or some other structure such as a ground plane or counterpoise...... Remember, all RF generators are TWO terminal devices, and the voltage is the voltage between the two terminals, not between one terminal and some other point located on Mars....... This potential difference sets up an Electric field, and the attendant electron motion sets up an H field, and thus an energy wave propagates....... > > How about a half-wave antenna (end-fed zepp)? Assuming it's being fed by > coax, would you suggest the counterpoise is the ring making up the shield of > the coax right where the coax stops and the antenna starts? > ***** End fed Zepps radiate from the feedline as well as the driven element, and usually open wire line and not coax is used as a feed. I've never seen a coax fed Zepp, tho I think it would probably work OK with the proper matching at the transmitter.... The coax shield is part of the radiating system, as you can verify with an EZNEC simulation and looking at the pattern... The Zepp is just a version of a dipole. The ARRL handbook tells all about the difficulty of matching the Zepp as a result of feedline radiation..... ***** Dipoles have one half of the antenna connected to one terminal of the RF generator and the other hald of the antenna connected to the other terminal.... If link coupling is used, neither part of the antenna is connected to the generator, but to a transformer, which then becomes the "new" generator output....... I have never seen any system at all, in any book, that uses a one terminal RF source, ----- there ain't no such animal. It's like a one terminal car battery....... saves connectors but won't start the car... :>)))))))) --- and I have used the coax as half of a radiating dipole simply by looping it thru some ferrite at a quarter wave from the feed point. A wire is half the dipole and the coax feedline is the other half..... It ain't rocket surgery to use the coax outer shield as a radiating structure.... If the dipole is mounted vertically, you have what can be advertised as a "no ground plane" vertical.....---- the radiating portion of the feedline forms half the dipole..... ***** Perhaps we are merely disagreeing on semantics. That's OK.... My stuff works --- your stuff works...... Maybe we just look at things differently........ I suspect it's too late for either of us to want to change our understanding of how the world works... :>)))))) Andy W4OAH > I would like to hear from someone like Roy as well, since I certainly am > well outside of any areas of significant experience here. > > ---Joel ***** Yeah.... Where's Al Gore now that we need him ??? :>))))))) Article: 98110 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: What is a wire antenna's impedance? -followup Message-ID: References: <7T9tg.15155$Wh7.1326@trnddc07> <1153256978.081184.264550@p79g2000cwp.googlegroups.com> <12bqlmvsdbhisb2@corp.supernews.com> <1153262499.873796.22260@h48g2000cwc.googlegroups.com> <12bstjoj1act014@corp.supernews.com> <1153350758.355083.197900@h48g2000cwc.googlegroups.com> Date: Thu, 20 Jul 2006 00:15:03 GMT On 19 Jul 2006 16:12:38 -0700, "AndyS" wrote: > >Joel Kolstad wrote: >> >> If I take a charged sphere with 1V applied, the E field falls off as 1/R all >> the way out to infinity; it is only there that it's actually zero, yes? >> > >***** One volt with respect to what other point ?? > > The RF generator >which drives the antenna has TWO terminals. If one terminal is >connected >to the wire, or the sphere, the OTHER terminal must be connected to >something else for the antenna to radiate. Hence, one terminal is >connected >to one side of the antenna, balanced or unbalanced, and the other >terminal is connected to either the other side of a balanced antenna, >or >some other structure such as a ground plane or counterpoise...... >Remember, all RF generators are TWO terminal devices, and the >voltage is the voltage between the two terminals, not between one >terminal and some other point located on Mars....... >This potential difference sets up an Electric field, and the attendant >electron motion sets up an H field, and thus an energy wave >propagates....... > >> >> How about a half-wave antenna (end-fed zepp)? Assuming it's being fed by >> coax, would you suggest the counterpoise is the ring making up the shield of >> the coax right where the coax stops and the antenna starts? >> >***** End fed Zepps radiate from the feedline as well as the driven >element, > and usually open wire line and not coax is used as a feed. I've >never > seen a coax fed Zepp, tho I think it would probably work OK with >the > proper matching at the transmitter.... The coax shield is part of >the The coax or balanced line is not the radiating system the though it may interact some it's the matching network from the low (under 600ohm) to high (>3000ohm) impedence at end of the halfwave antenna. Coax can be used but since one end is mismatched from it's characteristic impedence it could be lossy. Usually it's not as the matching section is small (~1/4 wave). In practice it works very well and there are antennas like Spertof (sp??) and other coaxial fed antennas are very succcessful. Allison > radiating system, as you can verify with an EZNEC simulation and > looking at the pattern... The Zepp is just a version of a dipole. > The ARRL handbook tells all about the difficulty of matching > the Zepp as a result of feedline radiation..... > >***** Dipoles have one half of the antenna connected to one terminal >of the RF generator and the other hald of the antenna connected to the >other terminal.... If link coupling is used, neither part of the >antenna is >connected to the generator, but to a transformer, which then becomes >the >"new" generator output....... I have never seen any system at all, >in any >book, that uses a one terminal RF source, ----- there ain't no such >animal. >It's like a one terminal car battery....... saves connectors but won't >start the car... >:>)))))))) > >--- and I have used the coax as half of a radiating dipole simply by >looping it thru some ferrite at a quarter wave from the feed point. >A wire is half the dipole and the coax feedline is the other half..... >It >ain't rocket surgery to use the coax outer shield as a radiating >structure.... >If the dipole is mounted vertically, you have what can be advertised as > >a "no ground plane" vertical.....---- the radiating portion of the >feedline >forms half the dipole..... > > >***** Perhaps we are merely disagreeing on semantics. That's OK.... >My stuff works --- your stuff works...... Maybe we just look at things >differently........ I suspect it's too late for either of us to want >to change >our understanding of how the world works... :>)))))) > > Andy W4OAH > > >> I would like to hear from someone like Roy as well, since I certainly am >> well outside of any areas of significant experience here. >> >> ---Joel > > >***** Yeah.... Where's Al Gore now that we need him ??? :>))))))) Article: 98111 of rec.radio.amateur.homebrew From: tim gorman Subject: Re: could VFO frequency be below IF ? References: <1153295684.841238.155880@i3g2000cwc.googlegroups.com> Message-ID: Date: Wed, 19 Jul 2006 21:45:35 -0500 aadu.adok@gmail.com wrote: > > > hi, > > I'm experimenting with my superhet. My IF is 8mhz (cause I have 8 mhz > crystals for IF filter). I first experimented on 40m. VFO was 15mhz. At > design time I'm using 3 meters long wire as an "antenna" (and I'm > sitting in my basement). I heard different european stations (EA5FKX, > RW6XE, UR4GI etc) which are several thousand km-s away. Pretty amazing > for such "antenna"! > > So I decided to go for 20m band. I had an option to set my VFO either > to 6mhz or 22mhz. I first went with 6mhz. But for my disappointment I > heard nothing but the band noise. > > So I'm confused now - is it because the short "antenna" or am I wrong > thinking that VFO 6mhz + IF 8mhz should give me 14mhz? > > any ideas? The frequency schemes should work fine. Be sure you don't have a high pass filter somewhere between your vfo and your mixer. I don't know what kind of mixer you are using but if it is an active mixer then there could easily be some kind of filter involved. That's why I like diode ring mixers with resistive pads between the vfo and the mixer - it gives you a good termination for both the mixer and the vfo and there isn't nearly as much to worry about. tim ab0wr Article: 98112 of rec.radio.amateur.homebrew Message-ID: References: Subject: Re: toroid cores? From: nospam@geniegate.com (Jamie) Date: Thu, 20 Jul 2006 10:54:30 GMT In , "Gregory D. MELLOTT" mentions: > My luck (quite some time ago) with FETs was not nice either. Someone may have to >correct my, yet the only way I think one can get away with fiddling with the >things the way most people construct, might be to use zener diodes between the >gate and source and drain. Some day... I'm going to mess about wit zener diodes... I tried to always keep myself grounded, pinching the leads together with a hemostat, but.. maybe the soldering iron did it, yea, uh huh. :-) > Once its all together and apparently functioning one >probably could remove them then with less worry about then getting a little >static jolt and ruining the junction. Tubes are a lot more forgiving. I hear ya about tubes being more forgiving, much more fun, too. Just wish they didn't have such weird power requirements. Jamie -- http://www.geniegate.com Custom web programming guhzo_42@lnubb.pbz (rot13) User Management Solutions Article: 98113 of rec.radio.amateur.homebrew Date: Thu, 20 Jul 2006 11:07:38 +0000 From: Scott Subject: Re: toroid cores? References: Message-ID: Actually, maybe the soldering DID do it. Are you using an iron with a three prong cord? The third prong ties the soldering iron tip to ground (assuming that, if so, you are plugging that into a GROUNDED three prong outlet and not using one of those three prong to two prong adapters). Also, this is assuming you are in the United States...not sure about other countries outlet wiring. Scott Jamie wrote: > Some day... I'm going to mess about wit zener diodes... I tried to always > keep myself grounded, pinching the leads together with a hemostat, but.. > maybe the soldering iron did it, yea, uh huh. :-) > > Jamie Article: 98114 of rec.radio.amateur.homebrew From: "AndyS" Subject: Re: Newbie Question: PC Based Oscilloscopes Date: 20 Jul 2006 09:08:37 -0700 Message-ID: <1153411717.246672.73210@75g2000cwc.googlegroups.com> References: <1153260845.004678.264980@p79g2000cwp.googlegroups.com> Joel Kolstad wrote:), I'm willing to bet > you'd be just as happy as with your old analog scope. > Andy comments: I admit that I haven't used a digital scope since I retired 5 yrs ago, but , in my opinion, they have TOO DAMN MANY buttons !!!! It was frustrating to have to use a new digital scope that I was unfamiliar with whenever I had to visit a different lab and give a hand.... Took longer to figure out the scope than to solve the problem...... "You might can teach an old dog new tricks, but only if he wants to learn them" :>)))) ..... from The World According to JungleAndy (W4OAH) : Article: 98115 of rec.radio.amateur.homebrew From: "Brian" References: Subject: Re: toroid cores? Message-ID: Date: Thu, 20 Jul 2006 17:46:50 GMT Jamie, Go to http://www.kitsandparts.com and use the toroid calculator he has there. Another thing you can try is wrapping 25 or 30 turns and then measuring it with an LC meter in the L mode of course. AADE sells a fantastic LC meter kit for about $100 - I built one a few years ago and I use it every week when digging in the junk box looking for caps and coils. Good luck with your regen, have fun. 73 de KB9BVN -- ========================================= Radio Amateurs - Fill your junk box, from my junkbox! http://www.hamradparts.com 73 de KB9BVN ========================================= "Jamie" wrote in message news:Lc1152868412193490xc2a48c@air.tunestar.net... > Hi Newsgroup, > > Been trying to make a regen radio out of garbage. So far, I seem to have > all the parts and it almost seems to work, however, I'm a bit confused > about the inductance of toroid cores. > > I've tried to use one of those things from the back of a monitor (presumably > to prevent RF interference) as one of the coils and another adjustable coil > from another device, to no avail. It has no markings and it appears to be > a ferrite device in the shape of a ring. > > Anyone know an easy way to figure out how many turns to get (presumably 300mh?) > from one of these? Can I measure it with a ruler and some how get a formula > for the number of turns / mH ? Are these really bad deviced to use? (the thought > occurs I must admit, that if it was meant to BLOCK rf, using would be illogical) > > Here's the circuit I'm basing it on: > > http://www.tricountyi.net/~randerse/regen.htm > > If I inject a signal directly into the coil (in place of his amplified RF "front > stage") I can pick it up, but no oscillation and lousy tuning. (comes in on pretty > much 1/2 the dial) I'm assuming this has something to do with the tank circuit. (I have > two air capacitors totalling around 360pf one from a console stereo, the other from > some place I can't remember where..) > > He's got 25T and 23T specified for a T-50-2 coil. Closest research on these that > I can find is that this should produce about 300mh (but I could be wrong! anyone know > for sure what the mH is on that?) This seems to make sense from everything I've read > so far, but.. I have no way to measure it. > > If I end up using an air core, would I keep the ratio of turns for the tickler and > injection coil? (where he has 3 and 5 turns spec'd) ? It's my assumption that > in these two smaller coils, it's a step up transformer so it'd be a matter of ratios, > am I correct in this assumption? > > Every bit of the circuit should come from garbage (the MPF102's I had to buy, but thats > it) Even the coil wire is from the transformer of a broken microwave, the LM386 chip used > for audio (and some resistors) will come from an old modem and the pot is a 500k pot, > (from a console) wired in parallel with a ~>10k resistor to give a range between 0 - 10k ohms. > > The main point is to build it from garbage, I already have a radio and don't > really "need" one, but.. as I once built a tube version of this (far simpler) > doing one in solid state appeals to me. > > Jamie > -- > http://www.geniegate.com Custom web programming > guhzo_42@lnubb.pbz (rot13) User Management Solutions Article: 98116 of rec.radio.amateur.homebrew From: "AndyS" Subject: Microwave oven transformers Date: 21 Jul 2006 05:42:50 -0700 Message-ID: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> Andy writes: I have been thinking about building a high voltage power supply for a big amp, and am toying with the idea of using a couple of microwave oven transformers, which I have on hand. I plan to use two, with the primaries connected in parallel but opposing, so that each one will supply voltage, half-wave, to a diode ring. By doing this, I can have each core grounded like it is used in the ovens.... So, has anyone else done this and run into any problems that I may not have forseen ? Thanks, Andy Article: 98117 of rec.radio.amateur.homebrew From: "Andrew VK3BFA" Subject: Re: Microwave oven transformers Date: 21 Jul 2006 07:25:24 -0700 Message-ID: <1153491924.564858.218020@s13g2000cwa.googlegroups.com> References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> AndyS wrote: > Andy writes: > > I have been thinking about building a high voltage power supply > for a big amp, and am toying with the idea of using a couple of > microwave oven transformers, which I have on hand. > > I plan to use two, with the primaries connected in parallel but > opposing, so that each one will supply voltage, half-wave, to a > diode ring. By doing this, I can have each core grounded like it > is used in the ovens.... > > So, has anyone else done this and run into any problems that > I may not have forseen ? > > Thanks, > Andy Drew VK3XU had an article in AR magazine recently about this - he used 2 of them, the primaries in series, the secondaries in //. He removed the magnetic shunts. With effectively half supply on each one, they didnt go into saturation but maintained full output voltag. He lifted the ground wire of the secondaries to frame - this was supposed to be a big no no, but his experiments showed there was no breakdown to earth, he then used a bridge rectifier on the resultant // secondaries...got good results,...... Andrew VK3BFA. Article: 98119 of rec.radio.amateur.homebrew From: "Kirk" Subject: Re: toroid cores? Date: 21 Jul 2006 12:35:15 -0700 Message-ID: <1153510515.846211.284510@m73g2000cwd.googlegroups.com> References: I soldered fets with a max V gate to source of 10 volts with no prob. The trick is to wrap the leads together with some bare 30 guage and then after soldering remove the 30 guage. Use a grounded iron and set the pcb on a sheet of aluminum foil with 470k - 1 meg to ground the resistor is to save you if you touch something leaky and the foil at the same time - like a bad scope or something. Kirk KC7THL > > Hi, > > My luck (quite some time ago) with FETs was not nice either. Someone may have to > correct my, yet the only way I think one can get away with fiddling with the > things the way most people construct, might be to use zener diodes between the > gate and source and drain. Once its all together and apparently functioning one > probably could remove them then with less worry about then getting a little > static jolt and ruining the junction. Tubes are a lot more forgiving. > > Sincerely, > > Gregory D. MELLOTT Article: 98120 of rec.radio.amateur.homebrew Date: Fri, 21 Jul 2006 16:50:52 -0700 From: Tim Wescott Subject: Re: Microwave oven transformers References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> Message-ID: AndyS wrote: > Andy writes: > > I have been thinking about building a high voltage power supply > for a big amp, and am toying with the idea of using a couple of > microwave oven transformers, which I have on hand. > > I plan to use two, with the primaries connected in parallel but > opposing, so that each one will supply voltage, half-wave, to a > diode ring. By doing this, I can have each core grounded like it > is used in the ovens.... > > So, has anyone else done this and run into any problems that > I may not have forseen ? > Using 1/2 wave rectification on each one will result in big DC currents in the coils. These DC currents will saturate your cores like nothing else. If you wanted to do this and be safe you'd want to rewind the primaries after insulating the core with some appropriate high-dielectric strength material like Kapton. If you're in the US you may want to consider using the primaries in series, and running off of 220V. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html Article: 98121 of rec.radio.amateur.homebrew From: Spammenotplease Subject: Re: Microwave oven transformers Date: Sat, 22 Jul 2006 00:29:19 +0000 (UTC) Message-ID: References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> There's a yahoo rfamplifiers group on the web, we've talked about this subject a few times and a copy of the text is available in our files section. Join us if you'd like to talk about hv supplies and rf amplifiers: http://groups.yahoo.com/group/rfamplifiers/ cheers, skipp : AndyS wrote: : Andy writes: : I have been thinking about building a high voltage power supply : for a big amp, and am toying with the idea of using a couple of : microwave oven transformers, which I have on hand. : I plan to use two, with the primaries connected in parallel but : opposing, so that each one will supply voltage, half-wave, to a : diode ring. By doing this, I can have each core grounded like it : is used in the ovens.... : So, has anyone else done this and run into any problems that : I may not have forseen ? : Thanks, : Andy Article: 98122 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: Microwave oven transformers Date: Fri, 21 Jul 2006 20:45:52 -0700 Message-ID: <12c37rlje2qau9b@corp.supernews.com> References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> Go to http://groups.google.com and do an advanced search for "microwave oven transformer" in rec.radio.amateur.*. You'll get a couple of pages of hits, representing at least a couple of hundred postings on the topic, many of them from this newsgroup. Roy Lewallen, W7EL AndyS wrote: > Andy writes: > > I have been thinking about building a high voltage power supply > for a big amp, and am toying with the idea of using a couple of > microwave oven transformers, which I have on hand. > > I plan to use two, with the primaries connected in parallel but > opposing, so that each one will supply voltage, half-wave, to a > diode ring. By doing this, I can have each core grounded like it > is used in the ovens.... > > So, has anyone else done this and run into any problems that > I may not have forseen ? > > Thanks, > Andy > Article: 98123 of rec.radio.amateur.homebrew From: df9gr@darc.de Subject: Input circuit for grounded grid amplifier with 2x 813 Date: 22 Jul 2006 08:39:03 -0700 Message-ID: <1153582743.878289.81760@p79g2000cwp.googlegroups.com> Hello, I got a pretty old amplifier with 2x 813 tubes in grounded grid. I runs nicely with 700 to 850 watts from 80 to 10m. I already did some modifications (vacuum relays, fan control, 9 band operation (80-10m) and now I am looking for some ideas for an input circuit. I meassured the input impedance of the tubes with about 120 to 130 Ohms which gives a bad SWR on a 50 Ohm output stage of a modern transceiver. I also tried a 1:4 UNUN. Results where slightly better but the SWR is still to high. As I want to avoid to use of an external tuner I am looking for someone out there who has build an input circuit (e.g. 1 collins pi-filter for every band) and can give me some advice how to calculate or build. tnx vy73 Rene DF9GR Article: 98124 of rec.radio.amateur.homebrew From: John - KD5YI Subject: Re: Microwave oven transformers References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> Message-ID: Date: Sat, 22 Jul 2006 16:24:42 GMT Tim Wescott wrote: > Using 1/2 wave rectification on each one will result in big DC currents > in the coils. These DC currents will saturate your cores like nothing > else. Hey, Tim - IIRC, there is only one diode attached to the transformer in my microwave. That would mean it is half-wave rectified as it comes from the factory. Yes? Cheers, John Article: 98125 of rec.radio.amateur.homebrew From: John - KD5YI Subject: Re: What is a wire antenna's impedance? -followup References: <7T9tg.15155$Wh7.1326@trnddc07> <1153256978.081184.264550@p79g2000cwp.googlegroups.com> <12bqlmvsdbhisb2@corp.supernews.com> <1153262499.873796.22260@h48g2000cwc.googlegroups.com> <5Whvg.5832$Lw.1536@trnddc07> <1153303250.437820.161760@75g2000cwc.googlegroups.com> Message-ID: Date: Sat, 22 Jul 2006 16:46:42 GMT AndyS wrote: > John - KD5YI wrote: > >>Where is the counterpoise on a handheld transceiver? I believe it is the >>body of the transceiver, the hand, arm, and body of the operator, and the earth. >> > > ****** Yes. If the case is conductive. Even if the case is metal , > and not > connected to the internal "ground" , it becomes part of the > counterpoise > by capacitance. Of course, the hand is conductive, etc..... > > > So, I tried to make > >>some measurements to show how much variation there can be with wire antennas >>and to underscore the fact that there is no way anyone can predict what a >>wire antenna's impedance will be on the objects the OP referred to under the >>myriad of conditions possible. >> > > \ > **** And you did that very effectively. I didn't realize that you were > trying > to show the significant variations, and thought you were wondering why > the readings were so different. Sorry,.... I just didn't get your > intent.... > > I would have liked to see what the piece of wire did with a nice ground > plane, tho, to see what the design baseline would have been.... In > other words, > a piece of wire looks like, say 32 ohms over a ground plane, but when > all the variables such as shape, no ground plane, people, nearby > objects, > etc come into play, it goes from hell to high water..... > I'm glad to see someone actually doing the experiments, rather than > just quoting a bunch of " E to the J Beta pitchforks" and letting it > go at that....... :>))))) > > Andy W4OAH Thanks for your comments, Andy. I agree with you on experiments. There are times, however, I would rather experiment using EZNEC than with the MFJ. It all depends on circumstances. One method can be faster than the other depending on the goal. In fact, it has been between 105 and 108 degrees here for the last week or two, putting a crimp in outside activities. I would rather stay inside and model my unusual thoughts than to try them outside. On the other hand, I don't know how to model an MFJ enclosure, my hand, my body, and such in EZNEC. So, that is when I measure. Also, there are times when both methods are warranted. Like, measure to determine if your model is correct. Or, model to determine if your test set-up is correct. Each method has its advantages and disadvantages. I just hope I have the knowledge to choose the appropriate method when it comes time to do the work. 73, John Article: 98126 of rec.radio.amateur.homebrew From: Bill Turner Subject: Re: Input circuit for grounded grid amplifier with 2x 813 Date: Sat, 22 Jul 2006 10:48:55 -0700 Message-ID: References: <1153582743.878289.81760@p79g2000cwp.googlegroups.com> ORIGINAL MESSAGE: On 22 Jul 2006 08:39:03 -0700, df9gr@darc.de wrote: >Hello, >I got a pretty old amplifier with 2x 813 tubes in grounded grid. I runs >nicely with 700 to 850 watts from 80 to 10m. I already did some >modifications (vacuum relays, fan control, 9 band operation (80-10m) >and now I am looking for some ideas for an input circuit. I meassured >the input impedance of the tubes with about 120 to 130 Ohms which gives >a bad SWR on a 50 Ohm output stage of a modern transceiver. I also >tried a 1:4 UNUN. Results where slightly better but the SWR is still to >high. As I want to avoid to use of an external tuner I am looking for >someone out there who has build an input circuit (e.g. 1 collins >pi-filter for every band) and can give me some advice how to calculate >or build. >tnx vy73 Rene DF9GR ------------ REPLY SEPARATOR ------------ Try an LDG autotuner: http://www.ldgelectronics.com/at-100amp.html This particular model is made for homebrewers to include in their amps. Bill, W6WRT Article: 98127 of rec.radio.amateur.homebrew From: "Guy Atkins" Subject: Wellbrook ALA 100 with Rotator - Construction Details Date: Sat, 22 Jul 2006 13:34:39 -0700 Message-ID: Those with an interest in building a Wellbrook ALA 100 setup for use on an antenna rotator may want to check out my most recent blog entry (July 22nd). I have pictures and construction details that describe the way I approached the project. I believe the ALA 100 is the most flexible and useful Wellbrook model for the do-it-yourselfer. You can construct the loop in whatever manner suits your abilities and requirements. My use of the ALA 100 is primarily for DXing foreign medium wave signals, with a secondary use of hearing third-world broadcasters on the tropical bands. I've heard of some amateur radio operators using Wellbrook antennas for a receive-only solution, too. 73, Guy Atkins Puyallup, WA USA blog: www.sdr-1000.blogspot.com Article: 98128 of rec.radio.amateur.homebrew Date: Sat, 22 Jul 2006 14:36:35 -0700 From: Tim Wescott Subject: Re: Microwave oven transformers References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> Message-ID: John - KD5YI wrote: > Tim Wescott wrote: > >> Using 1/2 wave rectification on each one will result in big DC >> currents in the coils. These DC currents will saturate your cores >> like nothing else. > > > > > Hey, Tim - > > IIRC, there is only one diode attached to the transformer in my > microwave. That would mean it is half-wave rectified as it comes from > the factory. Yes? > > Cheers, > John Yes, come to think of it -- yes. Perhaps the core is sized to take it. I guess the next question is how much harder can you push the system if you _aren't_ putting DC on the core? -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html Article: 98129 of rec.radio.amateur.homebrew From: "Roger (K8RI)" Subject: Re: Input circuit for grounded grid amplifier with 2x 813 Message-ID: References: <1153582743.878289.81760@p79g2000cwp.googlegroups.com> Date: Sat, 22 Jul 2006 18:20:57 -0400 On 22 Jul 2006 08:39:03 -0700, df9gr@darc.de wrote: >Hello, >I got a pretty old amplifier with 2x 813 tubes in grounded grid. I runs >nicely with 700 to 850 watts from 80 to 10m. I already did some >modifications (vacuum relays, fan control, 9 band operation (80-10m) >and now I am looking for some ideas for an input circuit. I meassured >the input impedance of the tubes with about 120 to 130 Ohms which gives >a bad SWR on a 50 Ohm output stage of a modern transceiver. I also >tried a 1:4 UNUN. Results where slightly better but the SWR is still to >high. As I want to avoid to use of an external tuner I am looking for >someone out there who has build an input circuit (e.g. 1 collins >pi-filter for every band) and can give me some advice how to calculate >or build. If resistive I always figured anything under 3:1 was good. I've fed a pair of 813s in GG at close to the legal limit with a fairly modern transceiver with good results, but I never checked to see what I had for an input impedance. I guess that was one of those cases where ignorance is bliss <:-)) I didn't know it was high so I didn't worry about it. For input impedance matching, look at a schematic of the Henry 2K4. They use a separate matching network plugged into an octal socket for each band. The ratios are different, but the design could easily be modified and the layout is easy to experiment with. I don't have the manual handy, but as I recall it's just an adjustable transformer with a tap. I think you'll be able to find the whole manual at BAMA Good Luck es 73 Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com (Get valid address from >tnx vy73 Rene DF9GR Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com Article: 98130 of rec.radio.amateur.homebrew From: Chris Jones Subject: Re: Microwave oven transformers Date: Sun, 23 Jul 2006 00:36:25 +0100 Message-ID: <12c5a2nom86qf6@corp.supernews.com> References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> Tim Wescott wrote: > John - KD5YI wrote: > >> Tim Wescott wrote: >> >>> Using 1/2 wave rectification on each one will result in big DC >>> currents in the coils. These DC currents will saturate your cores >>> like nothing else. >> >> >> >> >> Hey, Tim - >> >> IIRC, there is only one diode attached to the transformer in my >> microwave. That would mean it is half-wave rectified as it comes from >> the factory. Yes? >> >> Cheers, >> John > > Yes, come to think of it -- yes. Perhaps the core is sized to take it. > > I guess the next question is how much harder can you push the system if > you _aren't_ putting DC on the core? > Do they not put a capacitor in series with the transformer secondary, and then connect this combination to a diode in parallel with the magnetron? In this way the capacitor would prevent DC in the transformer. Chris Article: 98131 of rec.radio.amateur.homebrew From: miso@sushi.com Subject: Re: Wellbrook ALA 100 with Rotator - Construction Details Date: 22 Jul 2006 20:41:41 -0700 Message-ID: <1153626101.333721.76850@m79g2000cwm.googlegroups.com> References: Guy Atkins wrote: > Those with an interest in building a Wellbrook ALA 100 setup for use on an > antenna rotator may want to check out my most recent blog entry (July 22nd). > I have pictures and construction details that describe the way I approached > the project. > > I believe the ALA 100 is the most flexible and useful Wellbrook model for > the do-it-yourselfer. You can construct the loop in whatever manner suits > your abilities and requirements. > > My use of the ALA 100 is primarily for DXing foreign medium wave signals, > with a secondary use of hearing third-world broadcasters on the tropical > bands. I've heard of some amateur radio operators using Wellbrook antennas > for a receive-only solution, too. > > 73, > > Guy Atkins > Puyallup, WA USA > blog: www.sdr-1000.blogspot.com Ah, so your loops are concentric. I ran my parallel. Did you discuss this with Andy? Article: 98132 of rec.radio.amateur.homebrew From: "Mike Lucas" References: Subject: Push-pull CP640 amp Message-ID: Date: Sat, 22 Jul 2006 22:43:49 -0500 I'm looking for example circuits of a strong P-P RF amplifier using CP-640 fet's. I have four matched parts, and would like to improve over the single-ended amp's second order intermod. Any suggestions or links? Mike W5CHR Memphis, Tn. Article: 98133 of rec.radio.amateur.homebrew From: "Andrew VK3BFA" Subject: Re: Microwave oven transformers Date: 22 Jul 2006 21:48:17 -0700 Message-ID: <1153630097.294626.313050@i42g2000cwa.googlegroups.com> References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> John - KD5YI wrote: > Tim Wescott wrote: > > > Using 1/2 wave rectification on each one will result in big DC currents > > in the coils. These DC currents will saturate your cores like nothing > > else. > > > > Hey, Tim - > > IIRC, there is only one diode attached to the transformer in my microwave. > That would mean it is half-wave rectified as it comes from the factory. Yes? > > Cheers, > John No. Its actually a full wave voltage doubler - the tube itself is used as a diode. And there not, strictly speaking, "proper" power transformers - a saturable reactor would be a better description. They use this to current limit the things cheaply - notice the big "Boing" when they switch, noticeable on a low duty defrost cycle. 73 de VK3BFA. PS - as a self employed electronics technician, working alone, I refuse to work on the things in my business - too many people been lethally zapped by them, and no one nearby to give CPR...... Article: 98134 of rec.radio.amateur.homebrew From: "Guy Atkins" References: <1153626101.333721.76850@m79g2000cwm.googlegroups.com> Subject: Re: Wellbrook ALA 100 with Rotator - Construction Details Date: Sat, 22 Jul 2006 22:09:58 -0700 Message-ID: I did mention the spiral configuration to him, but he didn't comment on it. The construction seemed to be easier, so it's the only style I considered >from the start. Guy wrote in message news:1153626101.333721.76850@m79g2000cwm.googlegroups.com... > > Ah, so your loops are concentric. I ran my parallel. Did you discuss > this with Andy? > Article: 98135 of rec.radio.amateur.homebrew Subject: GE commercial controllers From: Allan Butler Date: Sun, 23 Jul 2006 00:30:07 -0500 Message-ID: <1153632045_23@64triton.net> There is a company that makes a controller for some of the commercial GE radios that have been around for several years. They allow control by computer or at a distance of about 100 feet from the control head using a standard computer microphone. Does anyone know the name of the company. I am interested in finding them and one or two of the radios so that I can play around a little bit. Thanks in advance. Yes I have done a search in Google. ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 98136 of rec.radio.amateur.homebrew From: "RHF" Subject: Re: Wellbrook ALA 100 with Rotator - Construction Details Date: 22 Jul 2006 23:27:19 -0700 Message-ID: <1153636039.570195.170200@p79g2000cwp.googlegroups.com> References: GA, Nice design and execution of the Wellbrook ALA 100 Loop Antenna as a portable and point-able (rotate) Antenna. A Close-Up Look : The Wellbrook ALA 100 Antenna with Rotor http://www.sdr-1000.blogspot.com/ The most flexible Wellbrook Antenna for the Radio Antenna Experimenter. ~ RHF . . . . Guy Atkins wrote: > Those with an interest in building a Wellbrook ALA 100 setup for use on an > antenna rotator may want to check out my most recent blog entry (July 22nd). > I have pictures and construction details that describe the way I approached > the project. > > I believe the ALA 100 is the most flexible and useful Wellbrook model for > the do-it-yourselfer. You can construct the loop in whatever manner suits > your abilities and requirements. > > My use of the ALA 100 is primarily for DXing foreign medium wave signals, > with a secondary use of hearing third-world broadcasters on the tropical > bands. I've heard of some amateur radio operators using Wellbrook antennas > for a receive-only solution, too. > > 73, > > Guy Atkins > Puyallup, WA USA > blog: www.sdr-1000.blogspot.com Article: 98137 of rec.radio.amateur.homebrew From: John - KD5YI Subject: Re: Microwave oven transformers References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> <1153630097.294626.313050@i42g2000cwa.googlegroups.com> Message-ID: Date: Sun, 23 Jul 2006 15:33:11 GMT Andrew VK3BFA wrote: > John - KD5YI wrote: > >>Tim Wescott wrote: >> >> >>>Using 1/2 wave rectification on each one will result in big DC currents >>>in the coils. These DC currents will saturate your cores like nothing >>>else. >> >> >> >>Hey, Tim - >> >>IIRC, there is only one diode attached to the transformer in my microwave. >>That would mean it is half-wave rectified as it comes from the factory. Yes? >> >>Cheers, >>John > > > No. Its actually a full wave voltage doubler - the tube itself is used > as a diode. Ah! Right you are, Andrew. I had forgotten about that. That makes Tim Wescott correct, too, about DC in the winding. Good catch. John Article: 98138 of rec.radio.amateur.homebrew Date: Sun, 23 Jul 2006 11:25:50 -0700 From: Tim Wescott Subject: Re: Microwave oven transformers References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> <1153630097.294626.313050@i42g2000cwa.googlegroups.com> Message-ID: Andrew VK3BFA wrote: > John - KD5YI wrote: > >>Tim Wescott wrote: >> >> >>>Using 1/2 wave rectification on each one will result in big DC currents >>>in the coils. These DC currents will saturate your cores like nothing >>>else. >> >> >> >>Hey, Tim - >> >>IIRC, there is only one diode attached to the transformer in my microwave. >>That would mean it is half-wave rectified as it comes from the factory. Yes? >> >>Cheers, >>John > > > No. Its actually a full wave voltage doubler - the tube itself is used > as a diode. > And there not, strictly speaking, "proper" power transformers - a > saturable reactor would be a better description. They use this to > current limit the things cheaply - notice the big "Boing" when they > switch, noticeable on a low duty defrost cycle. > I read an article years ago on using them for powering linear amps -- the first thing you were supposed to do was knock the shunt out of the core. Apparently this is usually quite easy unless it's spot welded, in which case it's quite hard. > 73 de VK3BFA. > > PS - as a self employed electronics technician, working alone, I refuse > to work on the things in my business - too many people been lethally > zapped by them, and no one nearby to give CPR...... > This could be wise -- once you broach the case on one of those things you're into voltages that will deal instant death. But that's the case for just about any tube linear amplifier. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html Article: 98139 of rec.radio.amateur.homebrew From: Telamon Subject: Re: Wellbrook ALA 100 with Rotator - Construction Details References: <1153626101.333721.76850@m79g2000cwm.googlegroups.com> Message-ID: Date: Sun, 23 Jul 2006 18:49:03 GMT In article , "Guy Atkins" wrote: > I did mention the spiral configuration to him, but he didn't comment on it. > The construction seemed to be easier, so it's the only style I considered > from the start. > > Guy > > wrote in message > news:1153626101.333721.76850@m79g2000cwm.googlegroups.com... > > > > Ah, so your loops are concentric. I ran my parallel. Did you discuss > > this with Andy? > > Spiral concentric or coil will change the pattern but since the antenna is so electrically small it won't make much difference unless you want to use the nulls. I would expect that a coil wound would be best. I you are concerned about using a null in the antenna pattern then go one turn. -- Telamon Ventura, California Article: 98140 of rec.radio.amateur.homebrew From: w8ji@akorn.net Subject: Re: Class C amps saturating? Date: 23 Jul 2006 19:00:23 -0700 Message-ID: <1153706423.121439.219690@m73g2000cwd.googlegroups.com> References: <1152683914.666244.144780@b28g2000cwb.googlegroups.com> Reg Edwards wrote: > ======================================= > All power amplifiers have a tuned circuit in the plate. It is > essential to reduce output power contained in the harmonics. > > In any case, power in the harmonics is wasted power. > > With a tuned circuit in the plate it is impossible to achieve a > rectangular voltage output waveform. It is always a sinewaveform. > > A rectangular plate current in conjunction with a tuned load always > causes harmonic power to be wasted at the plate. > > So one might just as well use a sinusoidal driving waveform, Class-C > or not. It's easier. It also avoids generating and wasting harmonic > power in the driver. Not true. A network with an inductive input will allow a square waveform at the device output but not waste significant energy in harmonics. I've done that in designs. In the 1950's RCA had an AM BC transmitter that drove a tube with a near square wave, and had a near square wave. The RCA transmitter used a low-mu triode that had parallel tuned circuits in the grid and anode set at the third harmonic. It had conventional networks feeding the grid and to the antenna from the plate resonantor. That transmitter made over 95% anode efficiency. 73 Tom Article: 98141 of rec.radio.amateur.homebrew From: w8ji@akorn.net Subject: Re: Surplus Sales of Nebraska Date: 23 Jul 2006 19:03:04 -0700 Message-ID: <1153706584.859740.182040@h48g2000cwc.googlegroups.com> References: <1152717559.138675.155040@m79g2000cwm.googlegroups.com> ars_wa8mea@netzero.com wrote: > I, like many hams, have gotten a lot of surplus stuff from Fair Radio > Sales in Ohio. > > Monday, I discovered Surplus Sales of Nebraska. > > Nice people! Old school customer service. The web ordering isn't > "modern". But they don't make a lot of money at this, I'm sure. So > I.T. people are probably out of the question. But your order gets > underway in about 48 hours..... > > They told me the owner spends all day on the net trying to hunt down > surplus stuff he can buy. So if you have anything, I was told to take > a photo of it....and send an e-mail to him. His e-mail address is at > the bottom of every web page. > > Here's the website for Surplus Sales: > > http://www.surplussales.com/ > > 73, Bill - WA8MEA > ars_wa8mea@netsero.com > http://HamRadioFun.com That's a good place to go if you don't mind paying more than new cost for some components. Fair Radio has great prices, Surplus Sales gets top dollar. Watch the price before you buy! Article: 98142 of rec.radio.amateur.homebrew From: et472@FreeNet.Carleton.CA (Michael Black) Subject: Re: Class C amps saturating? Date: 24 Jul 2006 02:13:04 GMT Message-ID: References: <1152683914.666244.144780@b28g2000cwb.googlegroups.com> <1153706423.121439.219690@m73g2000cwd.googlegroups.com> (w8ji@akorn.net) writes: > Reg Edwards wrote: >> ======================================= >> All power amplifiers have a tuned circuit in the plate. It is >> essential to reduce output power contained in the harmonics. >> >> In any case, power in the harmonics is wasted power. >> >> With a tuned circuit in the plate it is impossible to achieve a >> rectangular voltage output waveform. It is always a sinewaveform. >> >> A rectangular plate current in conjunction with a tuned load always >> causes harmonic power to be wasted at the plate. >> >> So one might just as well use a sinusoidal driving waveform, Class-C >> or not. It's easier. It also avoids generating and wasting harmonic >> power in the driver. > > > Not true. > > A network with an inductive input will allow a square waveform at the > device output but not waste significant energy in harmonics. I've done > that in designs. > And the point is that the Class-C only conducts on a portion of that sinewave anyway, requiring that tuned circuit in the output as a "flywheel" in order for there to be a sinewave at the output. The "harmonics" are a byproduct of that non-linear conduction at the input. And of course, that's why an amplifier could easily become a multiplier simply by tuning the output to a harmonic of the input signal. Michael VE2BVW Article: 98143 of rec.radio.amateur.homebrew From: David Subject: Biasing of Dual Gate Fets Message-ID: Date: Tue, 25 Jul 2006 05:32:40 GMT Hi, Pretty fundamental I know but can someone please explain the steps for setting up bias for a Dual Gate MOSFET. I know I could place a pot on the gate and source for each circuit and play with values but I would like a method that enables me to calculate the values. The main issue is how to determine values for Rs and Gate 2 Voltage. I am using BF998 and want to have a "play" at 5V and 8V supply. The formulae for Id is Id = Idss(1-Vgs/Vp) ^ 2 But Idss is stated as 2-18mA Vp Gate 1 is given as a range from 1-2V Vp gate 2 is given as range from 0.5 to 1.5V If I apply say 4V to G1 and 0V to G2, how do I calculate the voltage at the source to determine Vgs ? Any help much appreciated. Regards David Article: 98144 of rec.radio.amateur.homebrew From: w8ji@akorn.net Subject: Re: Class C amps saturating? Date: 25 Jul 2006 05:01:32 -0700 Message-ID: <1153828892.606330.180690@h48g2000cwc.googlegroups.com> References: <1152683914.666244.144780@b28g2000cwb.googlegroups.com> Michael Black wrote: > (w8ji@akorn.net) writes: > > Reg Edwards wrote: > >> ======================================= > >> All power amplifiers have a tuned circuit in the plate. It is > >> essential to reduce output power contained in the harmonics. > >> > >> In any case, power in the harmonics is wasted power. > >> > >> With a tuned circuit in the plate it is impossible to achieve a > >> rectangular voltage output waveform. It is always a sinewaveform. > >> > >> A rectangular plate current in conjunction with a tuned load always > >> causes harmonic power to be wasted at the plate. > >> > >> So one might just as well use a sinusoidal driving waveform, Class-C > >> or not. It's easier. It also avoids generating and wasting harmonic > >> power in the driver. > > > > > > Not true. > > > > A network with an inductive input will allow a square waveform at the > > device output but not waste significant energy in harmonics. I've done > > that in designs. > > > And the point is that the Class-C only conducts on a portion of > that sinewave anyway, requiring that tuned circuit in the output > as a "flywheel" in order for there to be a sinewave at the output. The point is Reg said a square wave would decrease efficiency and a sine wave was just as good, but that really isn't true at all. 73 Tom Article: 98145 of rec.radio.amateur.homebrew From: dkelly42@cox.net Subject: Re: Biasing of Dual Gate Fets Date: 25 Jul 2006 05:22:50 -0700 Message-ID: <1153830170.254671.314310@b28g2000cwb.googlegroups.com> References: Hi David, Some will ask what you are designing before they can give you an answer. FYI http://users.easystreet.com/w7zoi/lna50.htm Don David wrote: > Hi, > > Pretty fundamental I know but can someone please explain the steps for > setting up bias for a Dual Gate MOSFET. > Article: 98146 of rec.radio.amateur.homebrew From: "Andrew VK3BFA" Subject: Re: Microwave oven transformers Date: 25 Jul 2006 05:28:48 -0700 Message-ID: <1153830528.794122.46920@s13g2000cwa.googlegroups.com> References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> Tim Wescott wrote: > Andrew VK3BFA wrote: > > > John - KD5YI wrote: > > > >>Tim Wescott wrote: > >> > >> > >>>Using 1/2 wave rectification on each one will result in big DC currents > >>>in the coils. These DC currents will saturate your cores like nothing > >>>else. > >> > >> > >> > >>Hey, Tim - > >> > >>IIRC, there is only one diode attached to the transformer in my microwave. > >>That would mean it is half-wave rectified as it comes from the factory. Yes? > >> > >>Cheers, > >>John > > > > > > No. Its actually a full wave voltage doubler - the tube itself is used > > as a diode. > > And there not, strictly speaking, "proper" power transformers - a > > saturable reactor would be a better description. They use this to > > current limit the things cheaply - notice the big "Boing" when they > > switch, noticeable on a low duty defrost cycle. > > > I read an article years ago on using them for powering linear amps -- > the first thing you were supposed to do was knock the shunt out of the > core. Apparently this is usually quite easy unless it's spot welded, in > which case it's quite hard. > > > 73 de VK3BFA. > > > > PS - as a self employed electronics technician, working alone, I refuse > > to work on the things in my business - too many people been lethally > > zapped by them, and no one nearby to give CPR...... > > > This could be wise -- once you broach the case on one of those things > you're into voltages that will deal instant death. But that's the case > for just about any tube linear amplifier. > > -- > > Tim Wescott > Wescott Design Services > http://www.wescottdesign.com > > Posting from Google? See http://cfaj.freeshell.org/google/ > > "Applied Control Theory for Embedded Systems" came out in April. > See details at http://www.wescottdesign.com/actfes/actfes.html This could be wise -- once you broach the case on one of those things you're into voltages that will deal instant death. But that's the case for just about any tube linear amplifier. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Never thought about it that way Tim - but your quite right. Theres a familiarity with HV linear power supplies that I just dont have with uwave ovens - the linear supplies seem more "ordered" if that makes any sense -(it probably doesnt......possibly I am just seeking ajustification for not repairing them - their usually dirty stinking beasts... and they can throw some INCREDIBLE , mind boggling intermittents at ya...) Andrew VK3BFA. Article: 98147 of rec.radio.amateur.homebrew From: David Subject: Re: Biasing of Dual Gate Fets References: <1153830170.254671.314310@b28g2000cwb.googlegroups.com> Message-ID: <3Ioxg.560$rP1.18@news-server.bigpond.net.au> Date: Tue, 25 Jul 2006 13:07:11 GMT Don, Thanks for the link to Wes's experiments with MOSFETS. It still does not explain how to calculate the current or anything about datasheet specs. I understand some may be curious about what I might build. Typically it will be MOSFET amplifiers. My interest at present is the basic fundamental calcualtions that should be applied to determine Gate voltage and Source resistance for a self-biased Dual Gate MOSFET. If the calculations are the ones in my previous post then I need to know whether I use min or max values of IDss and Vp etc in the calculations. There must be some straight forward calculation steps for biasing a Dual gate MOSFET. I can find literally hundreds of articles for BJTs but cannot find much on Dual Gate MOSFET bias. I can see from the datasheets for example that best noise figure is when ID = 10mA. But cannot see how I calculate source resistance and Gate bias to end up with required VGS and ID. I don't want to pull out pots and play with VG2 and Rs combinations to find out what values set up the appropriate current. Regards David > Hi David, > > Some will ask what you are designing before they can give you an > answer. > > FYI > > http://users.easystreet.com/w7zoi/lna50.htm > > Don > > > > David wrote: >> Hi, >> >> Pretty fundamental I know but can someone please explain the steps for >> setting up bias for a Dual Gate MOSFET. >> > Article: 98148 of rec.radio.amateur.homebrew Date: Tue, 25 Jul 2006 15:08:47 +0100 From: Highland Ham Subject: Re: Microwave oven transformers References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> <1153630097.294626.313050@i42g2000cwa.googlegroups.com> <1153830528.794122.46920@s13g2000cwa.googlegroups.com> Message-ID: > Never thought about it that way Tim - but your quite right. Theres a > familiarity with HV linear power supplies that I just dont have with > uwave ovens - the linear supplies seem more "ordered" if that makes any > sense -(it probably doesnt......possibly I am just seeking > ajustification for not repairing them - their usually dirty stinking > beasts... and they can throw some INCREDIBLE , mind boggling > intermittents at ya...) +++++++++++++++++++++++++++ But there are some interesting and useful components to be taken before the remains are moved to the waste dump or perhaps recycling centre. Frank GM0CSZ / KN6WH Article: 98149 of rec.radio.amateur.homebrew From: "AndyS" Subject: Re: Microwave oven transformers Date: 25 Jul 2006 07:26:29 -0700 Message-ID: <1153837589.337241.48310@m79g2000cwm.googlegroups.com> References: <1153485770.076247.315190@s13g2000cwa.googlegroups.com> Highland Ham wrote:> +++++++++++++++++++++++++++ > But there are some interesting and useful components to be taken before > the remains are moved to the waste dump or perhaps recycling centre. > > Frank GM0CSZ / KN6WH Andy writes: Absolutely. The electronicc components can be used for a HV transformer, spare HV caps, and the timer is useful as a general purpose timer for a lawn sprinkler or oven reminder....for when your daughter is learning to cook.. The cabinet can be rigged with rubber bands and used to trap small animals in the garden The line cord can be used for many projects, or as a useful strangulation tool for serial killers... There's gold in them thar microwave ovens !!!!!! Andy W4OAH in Eureka ( the organically grown marijuana capital of Texas ) Article: 98150 of rec.radio.amateur.homebrew From: tim gorman Subject: Re: Biasing of Dual Gate Fets References: Message-ID: Date: Tue, 25 Jul 2006 11:06:20 -0500 David wrote: > > > Hi, > > Pretty fundamental I know but can someone please explain the steps for > setting up bias for a Dual Gate MOSFET. > > I know I could place a pot on the gate and source for each circuit and > play with values but I would like a method that enables me to calculate > the values. > > The main issue is how to determine values for Rs and Gate 2 Voltage. > > I am using BF998 and want to have a "play" at 5V and 8V supply. > > The formulae for Id is Id = Idss(1-Vgs/Vp) ^ 2 > But Idss is stated as 2-18mA > Vp Gate 1 is given as a range from 1-2V > Vp gate 2 is given as range from 0.5 to 1.5V > > If I apply say 4V to G1 and 0V to G2, how do I calculate the voltage at > the source to determine Vgs ? > > Any help much appreciated. > > Regards > > David One way of doing this is to get the datasheet for the FET you are using. There should be a graph that shows the operating characteristic curves. The x-axis will be Vds and the Y-axis will be the drain current Id. The characteristic curves will be for various levels of Vgs. Pick an operating point based on the type of amplifier you want. Let's suppose it will be Class A. Assume the FET has a power supply voltage of 40v and an Idss of 10ma. Let's say that you pick a point in the middle of the operating curves that gives an Id of 6ma and a Vds of 20v in order to get the maximum swing out of the amplifer. Looking at the characteristic curves shows that this will require a Vgs of about -1v. Now you have everything you need. If Vgs needs to be -1v and Id is 6ma (assume Id and Is will be the same) you need a resistor of Vd/Id (R = V/I) or about 166 ohms. The gate resistor you see in FET amps is not really there for biasing but more to set the input impedance of the amplifier. As long as the leakage current from the gate to the source is small, Vgs is set by the bias resistor in the source lead. tim ab0wr