In a message dated 6/17/04 10:53:15 PM Eastern Daylight Time, [EMAIL PROTECTED] writes:
> In the 1954 ARRL book: "Single Sideband for the Radio Amateur," W2UNJ > describes a phasing exciter. (The book was $1.50, by the way.) I have a later version of that book. No mention of the W2UNJ exciter. I do have articles where the 9 MHz generator/ 5 MHz VFO scheme is used. There is always a method of flipping the sidebands, because the heterodyne scheme doesn't do it. > > The equipment is long gone but as I recall, the plus or minus mixing > scheme reversed the sidebands. The math tells the real story. With a 9 MHz SSB generator and a 5-5.5 MHz VFO, the sidebands do not invert. But with a 5.2 MHz SSB generator and an 8.7-9.2 MHz VFO, the sidebands *do* invert. This is the case for phasing exciters. > > My recollection was a crystal filter system which was not the case. It does not matter whether the SSB is generated by the phasing or filter method. The sideband inversion or lack thereof is a result of subsequent heterodyning to the ham band desired. With a phasing system, sideband inversion is very easy. All you need to do is reverse the phase of one of the audio channels. A DPDT switch does the job. > > My point - as a throw away comment - was to recall the history of why > bands below 20m use LSB as the default SSB mode. And it was because of > the phase reversal due to the mixing scheme. Understood - except it doesn't work that way for a 9 MHz SSB generator and 5 MHz VFO. The math is not complicated - we simply add 5 MHz to the 9 to get on 20 and subtract 5 to get on 75. Either way the sideband does not invert. The bigger point, and the reason for all the bandwidth, is that we do ourselves and amateur radio a disservice if we blindly accept such stories without checking out the facts. What should a nonham think when presented with such a story, and then he/she does the math and discovers it doesn't work that way? 73 de Jim, N2EY _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net http://mailman.qth.net/mailman/listinfo/elecraft You must subscribe to post. Subscriber Info (Addr. Change, Unsub etc): http://mailman.qth.net/subscribers.htm Elecraft page: http://www.elecraft.com
