Trapezoidal modulation display (was "Re: [BC] Inovonics model 520")

[Alan Alsobrook]

You should use sample of the audio being applied to the input terminals 
of the transmitter. A spare processor output should work fine as long as 
the wave form is the same as being feed to the transmitter. Also be sure 
that you run it through an isolation 600:600 transformer, as you will be 
grounding one leg of audio to feed the scope.

X axis is typically the Transmitter input audio and the Y axis is the 
NON demodulated RF sample from the transmitter. Any appearance of a flat 
line to the small end of the trapezoid would indicate -100% modulation.

If you set the unmodulated carrier at +/- 1.6 Div then anything 
exceeding 4 div would indicate more than 125% modulation. Alternately if 
you move the base line to the bottom of the display then you can set the 
unmodulated carrier to 3.2 div so that anything above 8 div is over 125%.

Kira Mead wrote:
> Does the audio for the scope have to actually demodulated from the rf 
> sample, or can i simply get it from a spare output of the audio processor?


-- 
Alan Alsobrook CSRE AMD CBNT
St. Augustine Fl. 32086 904-829-8885
aalso at Bellsouth.net