It does not give the same sideband on 80 and 20. You also have to consider that the rotation of the tuning capacitor of the VFO turns the opposite direction for 20 as it does for 80. You will find this on the dial of many pre 1970 commercial offerings. Everyone needs to use one of the old SSB rigs for a few days to appreciate how good even the worst of today's rigs are. Then use a crystal controlled one or two tube transmitter and a 40s or 50s affordable receiver like a S-38 or NC-53 and appreciate how good the 60s SSB rigs were compared to the 40s and 50s.
Cookie, K5EWJ --- Ian White GM3SEK <[EMAIL PROTECTED]> wrote: > G4ILO wrote: > > > > > >GM3SEK wrote: > >> > >> What amazes me is the persistence of the belief > that it's all because a > >> 9MHz SSB generator and a 5MHz VFO produce > opposite sidebands on 14MHz > >> and 3.5MHz. Anyone who can rub two numbers > together can see that isn't > >> true... but that makes no difference at all. > >> > >9+5.0=14.0. 9+5.5=14.5. > >9-5.0=4.0. 9-5.5=3.5. > > > >Sorry, I don't see how that isn't true. I'm sure I > can also recall some > >published transceiver designs that took advantage > of this fact to provide > >two band coverage using a single VFO and 9MHz IF. > > This particular mixing process gives 3.5MHz and > 14MHz very conveniently > - but it gives the SAME sideband on both bands. > > Imagine a phasing-type SSB generator with a 9.000MHz > suppressed carrier > frequency. When configured for USB, an audio tone at > 1kHz gives output > in the upper sideband, at 9.001MHz. Then: > > 9.001 + 5.300 = 14.301 - that's 14.300MHz USB > 9.001 - 5.300 = 3.701 - that's 3.700MHz USB > > We have the SAME sideband on both 20m and 80m! > > To swap sidebands in this example requires the SSB > generator to be > switched to LSB. With a 1kHz tone, the output > switches to 8.999MHz. Then > the same calculations give: > 8.999 + 5.300 = 14.299 - that's 14.300MHz LSB > 8.999 - 5.300 = 3.699 - that's 3.700MHz LSB > > Once again, we get the SAME sideband on both 20m and > 80m. > > A 9MHz filter exciter is slightly different, because > it's the filter > passband that is centred on 9.000MHz. Such exciters > swap sidebands by > switching between carrier oscillators. For USB the > CO is below the > filter passband at 8.9985MHz, or for LSB the CO is > above the filter at > 9.0015MHz. The arithmetic is a bit more messy, but > the result is exactly > the same - generating SSB at 9MHz does NOT > automatically swap sidebands > between 80m and 20m. > > That is clear mathematical proof that the 9MHz SSB > exciters were NOT > responsible for the ham USB/LSB convention. On the > contrary, when > changing between 20m and 80m they were forced to > switch sidebands at > 9MHz in order to *follow* that convention! There is > also plenty of > historical proof that the USB/LSB convention had > been in existence for > several years before the first published 9MHz design > came along in 1956. > > > > > -- > > 73 from Ian GM3SEK 'In Practice' columnist > for RadCom (RSGB) > http://www.ifwtech.co.uk/g3sek > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
