On 16/01/2019 12:34, Chris Deacon wrote:
As a matter of interest, Bill, why has the software been written not
to allow TX below 200 Hz? I've always wondered.
73
Chris
G4IFX
Hi Chris,
it is partly for historical reasons. Prior to the introduction of using
a different Tx VFO dial frequency to centre the audio in the Tx SSB
filter passband (in fact before CAT control was even introduced) it was
important to avoid audio offsets below 200 Hz as a typical SSB filter
rolls off a lot in that region. That roll off impacts the signal doubly,
during Tx and Rx, by causing the MSK tones to be of unequal amplitude,
not a desirable outcome that will impact decoding sensitivity.
Now most users have CAT control and a reasonable proportion enable
"Settings->Radio->Split Operating" the requirement for Tx is not really
necessary but for Rx nothing has changed. A signal below 200 Hz is not
optimal and is discouraged.
73
Bill
G4WJS.
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