[BC] Outside source for checking Modulation Levels...

[Burt I. Weiner]

I have an IFR-1500.  It will measure 75 kHz when in the 
20kHz/Division Deviation position.  When I do this I usually kill the 
horizontal sweep so that I'm looking at the total deviation in one 
vertical line rather than spread out over the screen.  Sometimes I'll 
move the center carrier line to either the lower or upper edge 
graticule of the screen in order to see things a bit clearer.  Your 
biggest problem will be resolution under program conditions.  I 
sometimes use the analog meter on the right with it set to the "Peak" 
mode, but then you may have issues with meter ballistics under 
program conditions.  In the widest bandwidth position the IFR-1500 is 
pretty good out to around 100 kHz response.  Unfortunately, the 
internal modulator won't go out to 13+ kHz so you can't do Bessel 
Functions typically used for FM broadcast within the instrument, but 
I've done it using an external exciter and audio oscillator for 
calibration and that works quite nicely.

I can't speak for the IFR-1200 versions, but I suspect it would be 
essentially the same.

Wandering off subject for a moment... A few years ago I bought a "FM 
Exciter/transmitter" off of eBay for doing this kind of thing.  The 
one I bought didn't have an internal stereo generator but did have a 
baseband input spigot that could be fed with a stereo generator.  It 
came as two boards that I packaged in a small Hammond cabinet.  It's 
been great for doing Bessel Function calibrations and also for 
driving my Narda 3020A and Eagle Return Loss Bridges.  The exciter I 
bought for testing can be found at:

http://www.pcs-electronics.com/3000-next-generation-exciter-board-p-1317.html?osCsid=c1ba22e31566ca52896670f64d29f5ca

Burt

>From: Kevin Kidd <kkbroadcastengineering at gmail.com>
>
>Be sure to find out the max mod capability of their equipment.  I 
>don't recall the exact mod measurement capability of my IFR1500 but 
>I am sure that it is less than 75khz.  I think that it is 60khz and