[AMRadio] Monitoring Modulation Accurately


Bry Carling bcarling at cfl.rr.com
Fri Nov 15 10:16:19 EST 2013


Thanks for sharing these insights Steve.

Bry Carling
http://af4k.com

> On Nov 15, 2013, at 8:15 AM, Steve WA1QIX <wa1qix at piesky.com> wrote:
> 
> This topic has been talked about a lot over the years.
> 
> Using a scope to monitor your modulation gives you a good indication of the shape of your waveform, but the human eye is just not fast enough to catch the peaks nor can you really determine accurately your actual percentage of modulation unless you are using a very modern peak storing scope.
> 
> If you can see 100% negative modulation on a regular scope, chances are you are overmodulating very badly.
> 
> Measuring positive modulation on a scope without storage capabilities is, again, very difficult because the eye cannot see the fast peaks.
> 
> All real modulation monitors (as opposed to the CB "modulation meters") have a peak storage and display as part of the normal function of the instrumentation.  This is generally in the form of peak flashers, negative and positive.  Some more advanced instruments have a "peak hold" capability on the modulation percentage meters themselves.  This is really nice to have.
> 
> The other thing you get with a modulation monitor is a low distortion, high fidelity audio output.  This is very useful for listening off-air with headphones or for generating a recording of the demodulated signal.
> 
> Personally, I like a scope display but I *need* an accurate modulation monitor to show what's really going on and to give a high fidelity audio output for the headphones.
> 
> For many years, I used to run a modulation monitor and a scope at the same time.  Fortunately, with the advent of computers and modern displays, you can get both an envelope display and meters together (along with a whole lot of other features as well) in one unit.
> 
> Regards,  Steve
> 
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