D. Chester wrote:
One problem with monitoring the trapezoid pattern all the time is that
it will burn a dark vertical line onto the face of the scope tube,
where the unmodulated carrier appears. The trapezoid pattern is
useful for indicating the linearity of the modulated stage, but the
envelope pattern gives a better idea of the actual quality of the
signal, since flat-topping and waveform distortion are easily apparent.
The evelope pattern will burn a horizontal line where the bright
no-signal baseline appears, if you don't disable the scope when not
transmitting. This can also be a problem with CW and SSB operation,
since the bright baseline is there during pauses in modulation or
keying, just as the vertical line is there during pauses in AM
modulation when using the trapezoid pattern.
When I think of it, I usually use the trigger function of the scope.
Currently, on my dual trace, I've got the I.F. outputs of the receivers
(3 Sx-73's and 1 AR-88) tied into a pair of coax switches, so I can
switch between the receivers. It's a pretty neat way to check I.F.
linearity on the receivers. I can also tell a lot about the received
stations signal, as to where their audio is, how it's doing, and pretty
much basically what's happening with their signal.
AGC action, and non-linear I.F. stages preclude seeing any real decent
asymmetrical peaks... I think. That, or I've not seen any yet ;)
Let's plan a sked for this evening, Don. You pick the time and
frequency - I'll be there. We'll discuss more about scopes, and
patterns and so forth.
--
73, etc...
Geoff/W5OMR
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