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

[Kira Mead]

David - thanks for the information.
No I am not using a trapezoidal display.

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?


Thanks


Warren


> Perhaps <pirate at albanyis.com.au> is not using a trapezoidal display, which
> makes things pretty clear.
>
> For those who aren't familiar with this technique, you apply a sample of 
> the
> modulated RF carrier to the vertical input of the 'scope, and the 
> modulating
> signal to the horizontal input (don't use a sweep).
>
> The resultant display resembles a trapezoid (hence the name) that becomes 
> a
> triangle pointing to one side when modulation reaches 100% negative 
> modulation
> (carrier pinch-off). (The side to which the trapezoid/triangle points is
> determined by the relative polarity of the audio with reference to the 
> audio
> modulating the carrier).
>
> By setting the dead carrier in the exact center of the screen and 
> calibrating
> where the 100% neg. mod "point" occurs to, say, ten divisions from center,
> you can then use the horizontal scale on the scope screen to determine 
> pretty
> accurately the positive modulation in the direction opposite from the 
> negative
> modulation "point."
>
> Like an X-Y display of stereo audio, this setup offers the user a plethora 
> of
> information about the signal. With the trapezoid, you can see modulation
> level, density and amplitude and phase linearity.
>
> But, if nothing else, it's fun to watch. :-)
>
> Kind Regards,
> David
>
>
> David P. Reaves, III
> TransLanTech Sound, LLC
> Creators of the Award-Winning "Ariane Stereo Audio Leveler"
>
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