Date: Thu, 3 Nov 94 04:30:35 PST From: Ham-Homebrew Mailing List and Newsgroup Errors-To: Ham-Homebrew-Errors@UCSD.Edu Reply-To: Ham-Homebrew@UCSD.Edu Precedence: List Subject: Ham-Homebrew Digest V94 #324 To: Ham-Homebrew Ham-Homebrew Digest Thu, 3 Nov 94 Volume 94 : Issue 324 Today's Topics: 40 - 70 MHz crystal filter design antenna tuner buying help. FM Crystal Set (2 msgs) Interdigital Filters (2 msgs) Intermod Help! Program for desining low pass filters Source of ferrite cores Where does the power go Send Replies or notes for publication to: Send subscription requests to: Problems you can't solve otherwise to brian@ucsd.edu. Archives of past issues of the Ham-Homebrew Digest are available (by FTP only) from UCSD.Edu in directory "mailarchives/ham-homebrew". We trust that readers are intelligent enough to realize that all text herein consists of personal comments and does not represent the official policies or positions of any party. Your mileage may vary. So there. ---------------------------------------------------------------------- Date: 2 Nov 1994 14:46:15 GMT From: kirkland@bgtys22.bnr.ca (Bill Kirkland) Subject: 40 - 70 MHz crystal filter design Are there any articles or programs detailing design of crystal filters in the 40 - 70 Mhz range. Bill Kirkland ------------------------------ Date: 02 Nov 94 09:13:00 -0500 From: Bob.Klug@f239.n109.z1.fidonet.org (Bob Klug) Subject: antenna tuner Does anybody have plans for an easy-to-build antenna tuner? I am new to the shortwave listening hobby. For my birthday last year my girlfried bought me a "boat anchor" --a Blaupunkt model 40103 AM/FM/ Sw radio & phonograph player that is probably 25 years old. She got it at a local flea market for $25. I bought a 70 ft piece of stranded copper wire for an antenna and hung it in my attic. I get pretty good reception, but I read Harry Helm's book on shortwave listening and he recommends using an antenna tuner. I got plans for one from Panaxis but it involves winging 44 turns of wire around a core. This will be my very first attempt at building any equipment and I am afraid winding 44 turns of wire around a core and making 12 taps from it will be more difficult for me to get working than I realize. Can anybody offer me an easier-to-build model, or give me any other advice or encouragement? Thanks. Bob Klug --------- Fidonet: Bob Klug 1:109/239 Internet: Bob.Klug@f239.n109.z1.fidonet.org ------------------------------ Date: 28 Oct 94 19:58:28 CST From: rwitcher@vax1.umkc.edu Subject: buying help. just by the goddammed coors light, and be done with it. ------------------------------ Date: 2 Nov 94 17:43:27 GMT From: mack@mails.imed.COM Subject: FM Crystal Set Ian Mitchell asked how the crystal set works in digest #323. He correctly mentions that to receive FM it acts as a slope detector. A slope detector uses the selectivity curve of the tuned circuit to convert the FM into AM which is then detected by the diode. If all of the energy of the FM circuit is below the center frequency (Fo) of the tuned circuit, then frequencies closer to Fo will have higher amplitudes than lower frequencies. This has the effect of amplitude modulating the signal. Below is a model of what the selectivity curve of a single tuned circuit response looks like with Fo, Fc (the carrier of the FM), Fmax (high freq for maximum deviation of FM signal), and Fmin (low freq for maximum deviation of FM signal) shown. The name slope detection comes from using the slope of the Vout vs Vin curve as shown below. __|__ /| | \ / | | \ / | | \ / | | \ /| | | \ / | | | \ / | | | \ / | | | \ ______/ | | | \_______ | | | | | | | Fo Fmin | Fmax Fc There is an error in Ian's schematic. The diode detector MUST have a DC return to ground. Because of that I suspect that the .001 uF capacitor with L2 to ground should be deleted. Ray Mack WD5IFS mack@mails.imed.com ------------------------------ Date: 2 Nov 1994 01:57:45 GMT From: jdevenport@lanl.gov (Jim WB5AOX) Subject: FM Crystal Set Ian, the described circuit is only a regular run of the mill AM detector. I'd be interested in the results of such a circuit on FM, though since broadcast FM is SO broad it might well detect usable audio with slope detection. Slope detection of FM works on the principle that you tune to the "side" of an FM sig with an AM receiver and the frequency "wobbles" of the FM carrier come across as amplitude variations in the receiver since the signal strength is, in fact, varying as the frequency slides back and forth in and out of the AM receivers bandwidth (VERY wide in the case of similar crystal detectors with NO IF filtering). The audio thus recovered is not as loud as when using a good FM detector but if you have sufficient audio gain it produces quite usable results.... years ago while in college in the mid 1970's I homebrewed a simple walkie-talkie in a bud minibox using a VHF engineering transmitter strip and a simple converter in front of a garden variety AM protable transistor receiver.... it was so quiet with no signal present I didn't need squelch, it was very stable, and I could even separate fairly close (in frequency) repeaters so long as they weren't PHYSICALLY close! Wish I hadn't cannibalized it, that thing was a kick to use in front of old timer appliance op hams..... I also ( and you of course still can) have listened to many a 10 meter FM QSO with a normal AM rx. The trick is to tune in for maximum signal strength, then tune off to the "side" of the signal slowly until the audio becomes intelligible. It usually takes some tinkering to get the best audio, but if tuned properly it will produce surprisingly good audio. That crystal detector circuit likely would be so broad...... it may work fine since FM broadcast is on the order of 100 KHZ wide. And if 2 stations are fairly close to each other you likely know the result.... more than one song at a time or none, depending on how far apart they are in frequency. Jim Devenport WB5AOX ------------------------------ Date: Thu, 27 Oct 94 09:29:02 -0500 From: Richard Trok Subject: Interdigital Filters FROM:RTROK@radiohobby.chigate.com The program listing that you sent for Interdigital Bandpass Filters was received incomplete. It ended at Line 930. I am very much interested in this program and would appreciate it if you could resend it. Thanks Rich NI9S ___ X SLMR 2.1a X ------------------------------ Date: Thu, 27 Oct 94 09:28:00 -0500 From: Richard Trok Subject: Interdigital Filters TO:KA7OEI@uugate.wa7slg.ampr.org FROM:RTROK@radiohobby.chigate.com The program listing that you sent for Interdigital Bandpass Filters was received incomplete. It ended at Line 1320. I am very much interested in this program and would appreciate it if you would resend it. Thanks Rich NI9S ___ X SLMR 2.1a X ------------------------------ Date: 2 Nov 1994 01:40:04 GMT From: jdevenport@lanl.gov (Jim Devenport WB5AOX) Subject: Intermod Help! Are you SURE of the "cellular" tower being the source of the interference? if so, or if you know the main source of RFI and its frequency range, you can knock the bad interference down 20 to 30 dB (WADS!) with the installation of a simple coax notch filter. For 800 MHZ (cellular), merely cut a piece of RG-58 to approx. 2 1/4 inches, put a bnc fitting on one end, leave the other end open, and install it wit a tee fitting on your HT ant connection, the jpole coax going to the other port of the tee. For 450 MHZ, make the coax stub 6 1/4" long for 150 MHZ, make the stub 18 3/4" long The basic trick is to cut a coax stub to the 1/4 wave electrical length so the coax will resonate at the offending frequency. Since coax has a "velocity factor" in that rf travels more slowly thru it than solid copper wire or air, the velocity factor has to be "factored in". RG58 and may other types of flexible coax has a velocity factor of .6667 so you first find the 1/4 wave length: (example) 850 MHZ= 468 divided by 850; this is the half wavelength, then divide by 2 to get the 1/4 length (or simply start by dividing the desired freq into 234) , which should come out close to .275 feet or 3.3 inches, then multiply that by the velocity factor (3.3 X .67= 2.21 inches or very close to 2 1/4 inches. It helps to include the effective length of the BNC tee at this UHF frequency range... these make very effective notch filters but do have insertion loss, especially at frequencies near the notch frequency.... however getting rid of that much rfi may well outweigh any losses incurred. 73, Jim Devenport ------------------------------ Date: 2 Nov 1994 16:46:06 GMT From: ignacy@misz.animal.uiuc.edu (Ignacy Misztal) Subject: Program for desining low pass filters In , mack@ncifcrf.gov (Joe Mack) writes: >In article <395rsv$1bs@vixen.cso.uiuc.edu> ignacy@uiuc.edu (Ignacy Misztal) writes: >>I am looking for formula or at best a PD program to design low pass >>elliptic filters. I am also looking for help with filters that have >>all inductances the same. >> I forgot to say that these are transmitting filters made of coils and capacitances. Ignacy Misztal Ham radio: NO9E, SP8FWB E-mail: ignacy@uiuc.edu University Of Illinois 1207 W. Gregory Dr., Urbana, IL 61801, USA tel. (217) 244-3164 Fax: (217) 333-8286 ------------------------------ Date: Wed, 2 Nov 1994 15:09:39 GMT From: dstock@hpqmdla.sqf.hp.com (David Stockton) Subject: Source of ferrite cores David Crooke (dcc@dcs.ed.ac.uk) wrote: : My father (GM0RHP) is looking for a source of 4" long by 1/4" dia. ferrite : core rods to build some fancy antenna. The only source he knows of is in : California, USA - is there anywhere closer or am I best to just order them : on plastic and have them pop them in the post in a jiffy bag? : Dave I can probably help. I may even have something suitable in my junk box. I've not seen your dad for some time. There IS life in the UK on this group! Cheers David GM4ZNX ------------------------------ Date: Thu, 3 Nov 1994 02:57:29 GMT From: gary@ke4zv.atl.ga.us (Gary Coffman) Subject: Where does the power go In article <3998nm$c4c@sunb.ocs.mq.edu.au> guy@macadam.mpce.mq.edu.au (Guy Fletcher) writes: > >This is a rather different way of looking at the question, >hence the new thread. Considered comments welcome. You've said it much better than anyone else. The rest of us have been trying to stretch other models to say the same thing, sometimes without much success. If I may summarize, real power always flows towards the load, any heating in the amplifier is the result of loss of efficiency due to a poor load impedance at the amplifier output terminals. All else is chimera. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | emory!kd4nc!ke4zv!gary 534 Shannon Way | Guaranteed! | gary@ke4zv.atl.ga.us Lawrenceville, GA 30244 | | ------------------------------ Date: Mon, 31 Oct 1994 20:46:16 GMT From: kludge@netcom.com (Scott Dorsey) References<1994Oct30.045752.13121@ke4zv.atl.ga.us> <39164j$ohr@elaine.teleport.com>, <1994Oct31.001225.19727@ke4zv.atl.ga.us> Subject: Re: THE LITTLE RAZOR BLADE RADIO (UPDATE) In article <1994Oct31.001225.19727@ke4zv.atl.ga.us> gary@ke4zv.atl.ga.us (Gary Coffman) writes: >In article <39164j$ohr@elaine.teleport.com> burt@teleport.com (Burt Keeble) writes: >>So far, the only sources of high carbon steel that I have found are >>cutting implements (razor blades, carving blades, etc....). I would >>like a source that isn't potentially dangerous. >> >>Any suggestions? > >Chain saw bars, cold chisels, files, etc are all high carbon steel. Cast iron isn't high carbon steel, but works well for a steel detector anyway if you can get a polished section. Still, I always had better luck with copper oxide detectors myself (and copper oxide is everywhere, unfortunately). --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." ------------------------------ Date: Wed, 2 Nov 1994 15:05:52 GMT From: zlau@arrl.org (Zack Lau (KH6CP)) References<1994Oct25.153307.2220@ke4zv.atl.ga.us> <1994Oct25.204901.20098@arrl.org>, <1994Oct29.173008.10434@ke4zv.atl.ga.us> Subject: Re: Where does the power go? Gary Coffman (gary@ke4zv.atl.ga.us) wrote: : Class AB1 amplifiers routinely achieve 65% efficiency from DC input : to RF output in VHF TV broadcast service. Tubes certainly aren't : 100% efficient, but that's not because of some output impedance : resistor. It's because of contact resistance, back bombardment, : and plain old I^2R losses in the tube structure. Every attempt : is made to minimize these losses. Tube contact surfaces are silver : plated, and made large, tube structure lengths are minimized, and : suppressor grids are used in some cases. Flowing 12 amps at 8 kV : can cause a tube, and cavity, to heat, but not 48 kWs worth. 8000V/12 amps*.35=233 ohms Can you further break down these losses--how much is due to to each factor? I have to admit that I'm surprised that contact losses would be worth mentioning, particularly since they involve large, silver plated surfaces. I use cheap molex connectors with little tin plated contacts, and they aren't significant in a circuit with involving 2 amps at 12 volts (12V/2amps=6 ohms). -- Zack Lau KH6CP/1 2 way QRP WAS 8 States on 10 GHz Internet: zlau@arrl.org 10 grids on 2304 MHz ------------------------------ Date: Wed, 2 Nov 1994 01:59:06 GMT From: gary@ke4zv.atl.ga.us (Gary Coffman) References<1994Oct31.001225.19727@ke4zv.atl.ga.us> , <395svn$ksa@kelly.teleport.com> Reply-To: gary@ke4zv.atl.ga.us (Gary Coffman) Subject: Re: THE LITTLE RAZOR BLADE RADIO (UPDATE) In article <395svn$ksa@kelly.teleport.com> burt@teleport.com (Burt Keeble) writes: > >Well, how do I make a copper oxide detector? Maybe that would be a >better component? Think pennies. That green coating old copper pennies get is a copper oxide. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | emory!kd4nc!ke4zv!gary 534 Shannon Way | Guaranteed! | gary@ke4zv.atl.ga.us Lawrenceville, GA 30244 | | ------------------------------ End of Ham-Homebrew Digest V94 #324 ******************************