Posted by
N2EY on
Jun 17, 2004; 10:34pm
URL: http://elecraft.85.s1.nabble.com/K1-on-USB-CW-tp367868p367879.html
In a message dated 6/17/04 2:41:52 PM Eastern Daylight Time,
[hidden email] writes:
> The present day LSB - USB band "standards" have their roots
> from years ago in the availability of 9 Mc crystals / filters - when
> SSB was experimental and you had to build your own. 9 Mc plus a VFO
> running at 5.0 to 5.5 Mc gives you 20m USB. Subtract the VFO frequency
> and you tune "backwards" on 75/80m and you get LSB.
No, that's just not true. Urban legend. I believed it for years but when I
did the math the truth could not be denied. The only way you get sideband
inversion is if the heterodyne oscillator is above *both* the input and output
frequencies of a mixing process.
Yes, the 9 MHz IF / 5-5.5 Mhz VFO scheme was popular, and it does result in
one band tuning backwards. But it *does not* result in sideband inversion!
Generate USB and 9 MHz and mix it with a 5-5.5 MHz VFO and you get USB on 75 and
20.
The LSB/USB convention for hams goes back to before hams used 9 MHz filters
to generate SSB. .
Now if you use a 5 MHz SSB generator and a 9 MHz VFO you *do* get sideband
inversion.
If anyone wants the exact math, I have it all written up.
73 de Jim, N2EY
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