[BC] Scope for Mod Monitor...

[Robert Meuser]

Not really, Jerry. The FCC van I saw used a VFO and a frequency counter 
to calibrate the demodulator. You could also take the IF of the wideband 
demodulator and tap it off to a narrow band general coverage receiver 
and use it to determine the Bessel null.

R


Jerry Mathis wrote:

> On 7/19/06, Bill Croghan <loteng at lvradio.com> wrote:
>
>>
>>        The day I met Dane Erickson 25+ years ago, he was still 
>> working for
>> the FCC and started out handing me a polaroid of an oscilloscope showing
>> my
>> station over modulating.  Heck of a note to end my first week there.  He
>> showed me how they modulated an FM generator, watching for the nulls 
>> on a
>> spectrum analyzer that showed the proper modulation index for the 
>> defined
>> 100% modulation and observing the demodulated signal on an o-scpe.  They
>> then calibrated the vertical on the O-scope to that point, and started
>> watching the stations modulation.  The over modulation was obvious.  I
>> learned a lot that day!  I still use that system to check my own
>> modulation
>> monitors.
>>
>> Bill
>>
>> Bill Croghan CPBE WB?KSW
>> Chief Engineer,
>> KOMP/KXPT/KENO/KBAD
>> Lotus Broadcasting
>> Las Vegas, NV
>> Email to loteng (at) lvradio.com
>> Phone 702-315-3030
>> Fax      702-876-6685
>>
>>
>> I, and I bet others, would be interested to learn how you check FM
>> modulation with an oscilloscope.
>> -- 
>> JM
>> _______________________________________________
>>
>
>
> So you have to START with a Spectrum Analyzer, or a calibrated 
> demodulator.
> That's nice, if you have them.