Date: Tue, 1 Nov 94 04:30:41 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 #322 To: Ham-Homebrew Ham-Homebrew Digest Tue, 1 Nov 94 Volume 94 : Issue 322 Today's Topics: Collins S-line on 30 m.? (2 msgs) help! need in-amp filter formula (2 msgs) QRP transmittor circuit question 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: Sun, 30 Oct 1994 16:15:03 GMT From: pepperb@govonca.gov.on.ca (Brien Pepperdine) Subject: Collins S-line on 30 m.? Hello, I was wondering if anyone has had any positive success as putting a Collins S-line station on 30 m. I came across an old Hints and Kinks in a 1983 issue of QST. It said that basically (if I remember correctly) it was a matter of replacing the xtal in the 14.8 position normally used to receive WWV at 15 megs. with the proper (see manual) xtal to get it at 10 megs (then you have 30 meter operation as well as WWV at the 10 meg. freq.). The Hint said no re-tuning or alignment was necessary. I would like know if this does indeed work, indeed requires no re-tuning etc. (major at least) and that there is no problem afterward re. attendant harmonics. I ASSUME this should work, since the S-lines and KWMs were used for other freq. for military use, etc. Thank you, Brien VE3VAW pepperb@gov.on.ca ------------------------------ Date: Mon, 31 Oct 1994 18:07:08 GMT From: jma@ih4gp508.ih.att.com (na8130b00-Schaefer) Subject: Collins S-line on 30 m.? In article <1994Oct30.161503.7182@govonca.gov.on.ca>, Brien Pepperdine wrote: > >Hello, I was wondering if anyone has had any positive success as putting a >Collins S-line station on 30 m. I came across an old Hints and Kinks in a >1983 >issue of QST. It said that basically (if I remember correctly) it was a matter >of replacing the xtal in the 14.8 position normally used to receive WWV at 15 >megs. with the proper (see manual) xtal to get it at 10 megs (then you >have 30 >meter operation as well as WWV at the 10 meg. freq.). The Hint said no >re-tuning or alignment was necessary. >I would like know if this does indeed work, indeed requires no re-tuning >etc. >(major at least) and that there is no problem afterward re. attendant >harmonics. I ASSUME this should work, since the S-lines and KWMs were used for >other freq. for military use, etc. Well, I did it with my KWM-2. Also used one of the 10 meter positions for 12 meters. Works fine. As I recall the RX peaks up just fine and there is adequate grid drive for the finals. Might have a little less than optimum L/C ratio in the final tank circuits, but I use a tuned antenna system so didn't worry too much about harmonic rejection. 73 es gud luck es hpe cu on 30m. -- Ed Schaefer jma@ih4gp.att.com ham radio: K9JMA aviation: N97178 ------------------------------ Date: Fri, 28 Oct 1994 17:42:23 GMT From: tkreyche@zdlabs.ziff.com (Tom Kreyche) Subject: help! need in-amp filter formula Dear homebrewers, Digital guy needs help with analog circuit design! I'm driving a differential input delta sigma a/d converter with the "classic" instrumentation amp using three op amps (two in this case since the signal is differential in and differential out. The gain formula is simple, Vout = delta V * ((2*R2/R1) + 1). I also want to use the circuit to do some low pass filtering (get rid of 60 Hz), nothing fancy needed because of the characteristics of the converter and very low frequency application (25 Hz). I can't find the formula for determining C1 and don't know how to derive it. Looking at some tables, it appears the gain of the circuit (and therefore R1) affects the cutoff frequency. Thanks, Tom Kreyche KG6YJ |\ -----| \ | >----------- ---| / | | | |/ R2 C1 | | | |----------|--- | R1 | |----------|--- | | | | |\ R2 C1 ---| \ | | | >----------- -----| / |/ ------------------------------ Date: Mon, 31 Oct 1994 18:45:58 GMT From: tomb@lsid.hp.com (Tom Bruhns) Subject: help! need in-amp filter formula Tom Kreyche (tkreyche@zdlabs.ziff.com) wrote: : I also want to use the circuit to do some low pass filtering (get rid of 60 : Hz), nothing fancy needed because of the characteristics of the converter : and very low frequency application (25 Hz). I can't find the formula for : determining C1 and don't know how to derive it. Looking at some tables, it : appears the gain of the circuit (and therefore R1) affects the cutoff : frequency. : |\ : -----| \ : | >----------- : ---| / | | : | |/ R2 C1 : | | | : |----------|--- : | : R1 : | : |----------|--- : | | | : | |\ R2 C1 : ---| \ | | : | >----------- : -----| / : |/ The lowpass cutoff will be at 1/(R2*C1) (in radian frequency) or 1/(2*pi*R2*C1) in Hz. Above that, the circuit will do a 20dB/decade rolloff. HOWEVER, R1 DOES enter into it: it goes back "flat" when the gain reaches unity. So if the gain is 10 at DC, then there will be a 10:1 frequency range where the gain drops from 10 to 1; then it stays at 1 beyond that. Of course, the "corners" are rounded, but this should give you close to the right ansewer; there is a 3dB error at the "corner" frequencies. If the gain of this thing is high, the output will be close to differential, even if one input is "grounded." However, as the gain goes to unity (at higher frequencies), the output looses common mode rejection. This is something to watch for, if the ADC expects well-balanced differential inputs. Finally, if you want better filtering (without the levelling off at unity gain), then you can put a filter between the inputs: R in series with each input, and a C across the inputs. This provides no attenuation of common mode signals with frequency; you can get that with separate C's to ground, but then any mismatch will cause conversion of common mode to differential signals at frequencies in the vicinity of the filter cutoff. ------------------------------ Date: Mon, 31 Oct 1994 15:12:05 GMT From: mam@cbnews.att.com (mark.a.mccuistion) Subject: QRP transmittor circuit question This is a QRP Transmitter question: How come some circuit designs have the 'Final' transistor connected directly to the output filter and on to the antenna, but sometimes the output of the final transistor is sent to a coil, which then has another coiling wrapped over it, and that then goes to the output filter and antenna? Is one better than the other? The direct method is certainly easier - I have a lot of trouble doing coils and inductance and torids. I want to build a QRP rig, and easier is easier, but better is better, so If I have to do it the hard way to to it right, I'm willing (although not anxious.) Any advice on this acrea would be appreciated. --Mark KB2els mccuistion@attmail.att.com ------------------------------ Date: Mon, 31 Oct 1994 13:38:27 GMT From: kludge@netcom.com (Scott Dorsey) References , <38p0qj$ip6@elaine.teleport.com> Subject: Re: The Little Razor Blade Radio In article <38p0qj$ip6@elaine.teleport.com> burt@teleport.com (Burt Keeble) writes: >Scott Dorsey * >*Yup. You can even make a homebrew ribbon microphone with a couple of >*magnets, a transformer, and the foil from a Wrigley gum wrapper. But >*that's another thread. > >I would very much enjoy it if you created that thread. This >something-out-of-nothing stuff is very entertaining! The 1935 copy of "Hints and Kinks for the Radio Amateur" gives complete details on homebrew ribbon mikes. I pretty much copied the design given straight out of the book, although I used modern rare earth magnets for higher output, and halved the width of the ribbon in order to reduce mass. This issue also has an article on condenser microphone construction, but the design really isn't a good one. If you have access to a good, small machine lathe, check out Williamson's article _A Professional Condenser Microphone_ in the July 1963 issue of Audio. It's surprisingly quiet, even with the tube follower that they describe, and the machine work isn't as bad as you might expect. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." ------------------------------ End of Ham-Homebrew Digest V94 #322 ******************************