> character are shown. The radio still clicks pretty bad,
but only
> on the leading characters that follow a word-space (or
longer
> pause. Mid-word characters don't cause clicks with the mod
> in place.
Most radios hold off the transmitter until the synthesizer
settles. A few radios are design flawed in this area and
allow the radio to transmit while the synthesizer is moving
to the new TX frequency. The IC775DSP is a prime example of
this problem. It generates strong spurious signals that
appear briefly as the "oscillators" settle on new
frequencies when going from RX to TX. This problem can cause
a radio to have a normal looking waveform edge on a scope
but still generate a swooping click on key closure in QSK
modes as the local oscillators move to a new frequency. My
IC751A's do this when operating split.
A second issue is switching time. As circuits are
transferred, the radio can insert a hard leading edge.
A third and probably the most common problem is ALC. The ALC
voltage is zero when the radio is at rest. As the ALC
circuit initially charges, the leading edge gets a new slope
with a very sharp rise. Ten Tecs do this, as does the
1000MP. (Radios that don't do this generally have a RF drive
level control that allows you to set drive to a point where
minimal ALC is required on CW.) The Orion handles this by
"storing" the ALC level (transmitter IF gain) while you
receive, the Omni being older technology does not, and it
clicks on leading edges from ALC distortion of the waveform.
I'm sure there is an aftermarket Omni Six ALC mod on the web
someplace for Omni 6 owners.
By the way, this same problem occurs on SSB. It creates a
leading edge overdrive on SSB and a broadband spit. My
IC751A was so bad it showed on my peak reading SWR meter!!!
My Orion is totally clean, as is my FT1000D.
Many problems like this are not easily repaired. The only
easily corrected problem is ALC. You can often correct the
ALC induced click by applying intentional fixed external ALC
voltage from a negative supply. This negative voltage in
effect becomes a transmitter IF "manual gain control".
At least take heart in the fact that in some cases these
problems go away on manual or VOX operation to the point
where the start of a new word or series of characters has a
"pop" instead of each character hammering out a click. A few
occasional pops are not nearly as bad as the constant
pecking at the start of each dot and dash caused by poor
shaping. Some rigs have such fast ALC (and high IF gain)
they hammer on every rise.
I'd apply adjustable external bias to the ALC port and see
if it helps you out Mike. Might do the trick.
73 Tom
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|