|[AMRadio] New Year's Resolution-Getting Back on AM!|
ars.w5omr at gmail.com
Wed Dec 27 12:44:58 EST 2006
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.
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