[AMRadio] New Year's Resolution-Getting Back on AM!


Geoff/W5OMR 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.

--
73, etc...
Geoff/W5OMR




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