On 11/22/2011 4:04 PM, KU4AF wrote:
> Whatever the genesis of the LSB/USB convention on the ham bands,
> this conversion scheme wasn't it. Mixing a 9 MHz USB signal with a 5
> MHz VFO will produce a USB output on either 4 MHz or 14 Mhz. The
> sidebands only get inverted in a mixer when you subtract the SSB
> signal from a higher frequency
Try the math again ...
If you have a 5.0 - 5.5 MHz VFO and subtract a 9 MHz USB signal from
that VFO you end up with a LSB output that tunes from 4.0 - 3.5 MHz
in reverse. Start at 5.0 and subtract the 9 MHz carrier frequency you
get *minus* 4.0 MHz (carrier frequency) when the highest modulating
frequency (3 KHz or 9.003 MHz) is used you end up with *minus* 3.987
MHz - *lower sideband*! Do the same with the VFO at 5.5 MHz and you
will find LSB at *minus* 3.497 to 3.500 MHz.
A mixer can produce F2 +/- F1 just as easily as it produces outputs
at F1 +/- F2. If you don't believe this ... spend some time reviewing
the early SSB transmitter and receiver articles in QST from the 1950s
or borrow a Drake 1A/2A/2B and learn why some bands "tune backward."
73,
... Joe, W4TV
On 11/22/2011 4:04 PM, KU4AF wrote:
> Whatever the genesis of the LSB/USB convention on the ham bands, this
> conversion scheme wasn't it. Mixing a 9 MHz USB signal with a 5 MHz VFO will
> produce a USB output on either 4 MHz or 14 Mhz. The sidebands only get
> inverted in a mixer when you subtract the SSB signal from a higher frequency
> LO.
>
> This "ham legend" has persisted literally for generations despite frequent
> debunking. Maybe we can eradicate it by teaching our grandkids that "We had
> to use LSB back then because DSP hadn't been invented yet."
>
> John, KU4AF
> Pittsboro, NC
>
>
> w5tvw wrote
>>
>> <snip>
>> The reason this was done was due to the conversion process employed as
>> the
>> SSB signal was generated at 9 Mhz and heterodyned to either 14, or 4 Mhz
>> with a 5 MHz VFO signal. Whichever position of the mode switch was used
>> (SB1 in all probability, it's been too many years for me to precisely
>> recall
>> and not really important at this time for me to research it!) At any
>> rate,
>> the result was Upper sideband signals on 14 Mhz and lower sideband signals
>> at 3.8-4.0 Mhz.
>>
>
> --
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