Posted by
N2EY on
Jun 18, 2004; 10:57am
URL: http://elecraft.85.s1.nabble.com/K1-on-USB-CW-tp367868p367877.html
In a message dated 6/17/04 10:53:15 PM Eastern Daylight Time,
[hidden email] 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
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