[AMRadio] Use of an oscilloscope to monitor am audio


W7QHO at aol.com W7QHO at aol.com
Sat Mar 18 23:05:15 EST 2006


In a message dated 3/18/06 1:25:53 PM, w5jo at brightok.net writes:


> So I take my 10:1 probe and attach to the output of the balun terminals.
> One to the ground clip and the other to the probe.  That provides enough
> isolation to give a waveform display.
> 
> The waveform is very difficult to follow as to assure 100% modulation.  To
> be accurate, one should use the trapezoidal pattern.  The peaks and valleys
> of a waveform cannot be seen accurately on a scope unless you have a storage
> scope.  Others have suggested means of building a sampler for this purpose,
> and I thought I would mention another way.
> 
> 

I use a 100:1 probe on higher power rigs.

I don't find a "waveform" (amplitude vs. time) display difficult to 
interpret.   Over modulation in the negative direction shows up clearly as "pearls" on 
the baseline and positive peak levels can be easily read by slowing down the 
trace.   Flat-toping can be clearly seen at higher sweep speeds.   Admittedly, 
a trapezoid display can provide additional information but I've never found it 
worth the trouble.

Dennis D. W7QHO
Glendale, CA



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