Date: Fri, 19 Nov 93 04:31:00 PST From: Ham-Homebrew Mailing List and Newsgroup Errors-To: Ham-Homebrew-Errors@UCSD.Edu Reply-To: Ham-Homebrew@UCSD.Edu Precedence: Bulk Subject: Ham-Homebrew Digest V93 #107 To: Ham-Homebrew Ham-Homebrew Digest Fri, 19 Nov 93 Volume 93 : Issue 107 Today's Topics: Low-cost VHF amplifier application note single sideband 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: Tue, 16 Nov 1993 22:42:25 GMT From: world!dts@uunet.uu.net Subject: Low-cost VHF amplifier application note To: ham-homebrew@ucsd.edu In article gila005@uabdpo.dpo.uab.edu (Stephen Holland) writes: >In article , >holland@gasmac.dom.uab.edu (Steve Holland) wrote: >> >> One person asked about what application note had a reference to >> a vhF power amplifier. I got several frol motorola. One, a >> broadband 300 watt amplifier from 10 to 300 MHz was interesting >> until I saw the power transistor alone cost about $300 in quantity >> of one. A much more affordible amplifier was described in >> engineering Bulletin EB-90, Low-cost VHF amplifier has broadband >> performance. It uses the MRF 260 and MRF 262 and includes the >> PCB pattern in the note. 15 Watts output at 146 MHz. >> >> Darn, I realize I had another note for a higher note for a higher >> power amplifier which included an automatic T/R relay in the >> design. I'll post on that when I bring it into work. > >The other note of interest is AN-791m a 75W and 35W power amp optimized >for 144-148 MHz. It has a built in carrier operated relay, which stays >up in SSB and CW with a built in delay on releasing the relay. > >To the person who emailed me, the responses bounced. > >There are kits for these amps from communication concepts, >508 Millstone Drive >Beaver Creek OH 45434-5840 >513-426-8600 > >The 35 watt and 75 watt amps are $80 and $120 respectivley. > >Does anyone have experience dealing with them? > >Steve Holland I have built one of each size. The 75 watt one has been on a repeater for quite some time now (over a year). I had to rebuild it a while back because the RF sensing circuit was chattering the relay. I do not know why, but the amplifier was going into oscillation. For the repeater case, I just added a jumper so that when power is present, the relay is pulled down, putting the amp into line. The only reason I did not eliminate the relay altogether is that we want the amp out of line when the AC power fails. For repeater use, I added a fan on the heatsink. I loaned out the 35 watt model and a power supply to a new ham who had been in one of my ham radio classes (I do LOTS of elmering!) and it worked fine for a few days, then it developed the same problem with oscillation. Fixing this one is harder, since I really DO want the RF sense switch to work. I tried rebiasing the thing to class C, but there is still a problem with oscillation after the first time RF is applied. This one is going to wind up in the hands of the master (WA1RHP, an expert at solid state amplifiers), to see if he can get it to work. The old adage is true: you try to build an amplifier and you get an oscillator. Try to build an oscillator and you get an amplifier! If you are looking for a finished product, look at TE systems or RF Concepts. (Stay away from Mirage). -- --------------------------------------------------------------- Daniel Senie Internet: dts@world.std.com Daniel Senie Consulting n1jeb@world.std.com 508-365-5352 Compuserve: 74176,1347 ------------------------------ Date: Tue, 16 Nov 1993 13:15:36 GMT From: munnari.oz.au!spool.mu.edu!sdd.hp.com!hpscit.sc.hp.com!hplextra!hplb!hpwin052!hpqmoea!dstock@network.ucsd.edu Subject: single sideband To: ham-homebrew@ucsd.edu As has been already mentioned, good alternate sideband rejection still requires better than reasonably achievable gain and phase precision to get exact cancellation. Subtraction processes are always bad on accuracy requirement. I don't see anyone putting much more effort into this area. DSP is fast becoming cheap, and it is possible to create really good SSB at a low IF using DSP and the sort of 12 bit DAC aimed at the Graphics and DDS markets. This will give a system with no adjustments, no setting up, and no temperature stability problems. Receivers are more demanding and ADC performance development tends to lag DAC developments. There are receivers on sale that digitise a low IF and then use DSP, but ADC performance is not yet such as to allow competition with the best analogue filter based receivers. Ring-proof CW filters could prove popular! Cheers David GM4ZNX ------------------------------ Date: 16 Nov 1993 20:39:25 -0500 From: concert!news-feed-1.peachnet.edu!gatech!howland.reston.ans.net!sol.ctr.columbia.edu!news.mtu.edu!news.mtu.edu!not-for-mail@decwrl.dec.com To: ham-homebrew@ucsd.edu References <1993Nov13.164257.15906@cs.rit.edu>, <1993Nov14.020154.9354@ke4zv.atl.ga.us>, ia.edu Subject : Re: single sideband, phasing and T2/R2 Galen Watts (galen@picea.CFNR.ColoState.EDU) wrote: : In article <1993Nov14.020154.9354@ke4zv.atl.ga.us> gary@ke4zv.UUCP (Gary Coffman) writes: : >In article <1993Nov13.164257.15906@cs.rit.edu> atd@cs.rit.edu (Albert T Davis) writes: : >>I have been out of this for a while.... : >>Is the filter method still the most common for SSB generation? : >>It seems to me that the phasing method is far superior with today's technology : >>al. : >It remains difficult to achieve a precise 90 degree phase shift over : >3 octaves of audio frequencies. DSP offers the potential to solve that : >problem though. : >Gary Coffman KE4ZV | Life's a journey, | gatech!wa4mei!ke4zv!gary : >Destructive Testing Systems | not a destination. | uunet!rsiatl!ke4zv!gary : >534 Shannon Way | Live it. | emory!kd4nc!ke4zv!gary : >Lawrenceville, GA 30244 | | : In the April, 93 issue of QST is the 'Multimode Phasing Exciter' alias the : T2 board. Uses 1% componenets in the phase shift network. I have the board : (along with the companion R2) but I haven't built it, as I can't decide if : I should put it on 440 SSB or 1750m CW/SSB. You must also have a 90 deg. : phase shift for the RF, which I can get for 440 from Mini-Circuits. : Anybody built these boards and willing to talk? : Galen, KF0YJ Why buy a phase shifter for RF? ...just use a 1/4 wave piece of transmission line after the power divider... ------------------------------ Date: 16 Nov 1993 09:55:30 +0200 From: munnari.oz.au!spool.mu.edu!uwm.edu!cs.utexas.edu!howland.reston.ans.net!pipex!sunic!news.funet.fi!butler.cc.tut.fi!lehtori.cc.tut.fi!not-for-mail@network.ucsd.edu To: ham-homebrew@ucsd.edu References <2c4lhr$6pi@hpscit.sc.hp.com>, <1993Nov15.164550.18931@cs.rit.edu>, <2c8ohb$abo@hpscit.sc.hp.com>sunic Subject : Re: single sideband Richard Karlquist (rkarlqu@scd.hp.com) wrote: [about using phasing receivers] > Of course the problem with this method is you will be limited to > 40 dB. or so selectivity for the opposite sideband (which is really > the adjacent "channel" so to speak.) That is pretty lousy receiver > performance. This is a problem in crowded bands, but what about less crowded VHF/UHF bands ? Most likely the "adjacent" channel contains only white noise. Going from 0 dB opposite sideband suppression (DSB) to infinite (SSB) will improve the SNR by 3 dB. A very modest 10 dB opposite sideband suppression will give 2.5 dB improvement in SNR. On the transmitter side, if the most important factor is not spectral effiency, a 10 - 20 dB opposite sideband suppression should be enough. The reduction of the power level of the desired sideband would be hardly noticable. As long as such rigs are used only on bands with low activity, modest opposite sideband suppression should not hurt anyone. It is better to have some activity on these bands than no activity at all. Paul OH3LWR -------------------------------------------------------------------- Phone : +358-31-213 3657 X.400 : G=Paul S=Keinanen O=Elisa-Tampere A=ELISA C=FI Internet: Paul.Keinanen@Telebox.tele.fi Telex : 58-100 1825 (ATTN: Keinanen Paul) Mail : Hameenpuisto 42 A 26 FIN-33200 TAMPERE FINLAND ------------------------------ Date: 18 Nov 93 15:16:24 GMT From: ogicse!emory!kd4nc!ke4zv!gary@network.ucsd.edu To: ham-homebrew@ucsd.edu References , <2cbvcd$m8q@maxwell21.ee>, Reply-To : gary@ke4zv.atl.ga.us (Gary Coffman) Subject : Re: single sideband, phasing and T2/R2 In article jjw@seastar.org (John Welch) writes: >> Why buy a phase shifter for RF? >> ...just use a 1/4 wave piece of transmission line after the power divider... > > Unless you use Teflon coax, the variation in velocity factor >from foot to foot makes it difficult to get exactly 90 degrees by >calculating the length in inches. > A 90 degree length of coax at 160M is rather long. > A 90 degree chunk of coax is only 90 degrees at one very >narrow range of frequencies. > Unless you have a *lot* of patience and time, it's far easier >to use a pre-built component that you already know works. > A 90 degree chunk of coax induces some loss, and thus some >amplitude imbalance. > > I once seriously considered phasing using the Qualcom dual DDS >chip, setting the second DDS to be 90 degrees plus or minus from the >first, but differences in the DACs and filters induced too much >amplitude and phase shift for the sharp selectivity I wanted. I found >I could get what I wanted only if I also used a crystal filter too, >and at that point the expense of phasing became a drawback. I'd still >like to do it some day, though... There's a real simple way to get a 90 degree shift. Have your oscillator drive a divide by four circuit arranged as one JK driving two other JKs, one driven by Q and the other driven by not Q. You can take your quadrature components from the latter pair of FFs. Of course your oscillator must run at 4X the IF frequency, but that's not a problem. If you use HS parts for the JKs, your quadrature outputs will be nearly ideal square waves which is exactly what you want to drive diode ring mixers efficiently. Getting that blankety blank audio phase shift to be exactly 90 degrees at every frequency over a 3 octave range is still the hard part. Gary -- Gary Coffman KE4ZV | Where my job's going, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | I don't know. It might | uunet!rsiatl!ke4zv!gary 534 Shannon Way | wind up in Mexico. | emory!kd4nc!ke4zv!gary Lawrenceville, GA 30244 | -NAFTA Blues | ------------------------------ Date: 17 Nov 1993 03:38:08 GMT From: sdd.hp.com!hpscit.sc.hp.com!rkarlqu@decwrl.dec.com To: ham-homebrew@ucsd.edu References <1993Nov14.020154.9354@ke4zv.atl.ga.us>, , <2cbvcd$m8q@maxwell21.ee> Subject : Re: single sideband, phasing and T2/R2 In article <2cbvcd$m8q@maxwell21.ee>, Daniel E. Carlisle wrote: >Galen Watts (galen@picea.CFNR.ColoState.EDU) wrote: >: (along with the companion R2) but I haven't built it, as I can't decide if >: I should put it on 440 SSB or 1750m CW/SSB. You must also have a 90 deg. > >: Galen, KF0YJ > >Why buy a phase shifter for RF? >...just use a 1/4 wave piece of transmission line after the power divider... > The 1/4 wave line gets kinda long on 1750m! ------------------------------ End of Ham-Homebrew Digest V93 #107 ****************************** ******************************