The LSB or USB transmit signal is produced in the balanced modulator,
and then filtered to remove the unwanted sideband. The DSB signal that
is eventually run through the filter, to remove the unwanted sideband is
generated by combining the voice audio with the BFO. The signal produced
by the balanced modulator is supposed to be a clean double sideband
signal, with very little carrier. The carrier balance adjustment nulls
the carrier, and any residual carrier is further attenuated by the SSB
filter. What is left of that DSB signal after passing through the 2.4
kHz filter is dependent on the BFO frequency and the shape of the
filter. If it sounds real good using one sideband, and not good using
the other, they are really only two possible causes either 1) the BFO
frequency is wrong or 2) the filter has poor symmetry. (This assumes
there is not something else changing, that should not change, when you
change sidebands, such as some control signal which should be identical
for both sidebands, but somehow changes. For instance, the balanced
modulator gets unbalanced to produce CW. It the logic that controls that
is messed up, and unbalancing the modulator in one SSB mode, that could
be a problem. A leaky diode or bad gate in the control logic might do
that.) The only things that should change between operation on LSB
versus USB is the BFO frequency, and some correction to the frequency
readout, or shift of some other oscillator to make the frequency display
correct. There should be no change in the audio level or frequency
response feeding the balanced modulator, and no change in the way the
balanced modulator works.
Most SSB filters are not perfectly symmetrical, and there will be some
minor difference in the sound of your transmitted signal when switching
sidebands. The difference should be something you really have to listen
carefully to notice. It should not be such a big difference that it
sounds "bad" on one sideband and "great" on the other.
How have you confirmed the BFO frequencies are correct?
DE N6KB
On 4/5/2014 4:34 PM, Mark Kenward wrote:
i have set Reference oscillator , and the BFO's on the rig.
Rig is on frequency as discussed a week or so ago.
My issue is this.
USB sounds great on transmit.
LSB, however, is thin. Narrow, like you are talking through a 1.8-2.1 kHz
filter.
I tried another 2.4 filter in 9mHz slot, with no change.
Can someone tell me what to adjust to move the USB and LSB transmits more to
the center of their respective ranges.
I am happy with the rig so far, but it is obvious that LSB needs an adjustment,
and of course, it is not the BFO.
I have a friend who wants the rig, and I would like to make it perfect for him.
Thanks for any help.
Mark
K8VF
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