CF 87.141 requirement

[dolgaleb]

I have to test a radio with a carrier frequency of 100 MHz which is AM modulated.
I have to verify if the radio meets the CF 87.141 requirements. In specific:

"On 100 MHz at least thirty per cent of the total power emitted during any transmission cycle with or without modulation must be contained within plus or minus 30 Hz of the carrier frequency."

Can anybody explain this requirement and how to test for it?

Thanks in advance.

 

[BradtheRad]

It means your carrier oscillator must be rigidly reliable so that it deviates very little from 100 MHz. Howsoever it derives initially, it should not be affected by other circuitry. One thing that helps is rock-solid regulation of the power supply. If you use a crystal then it would help if you make a constant temperature for it (crystal oven).

Your frequency counter must detect change within 30Hz. Just maybe you can include pre-scaling or lissajous figures to take readings. Your frequency is within the commercial FM band however amplitude modulation might interact in unexpected ways with frequency modulated airwaves.

 

[G4BCH]

The requirement is often referred to as 'Occupied Bandwidth' A search for 'measure occupied bandwidth' gives plenty of information.
You will need a spectrum analyser to measure it.

 

[FvM]

I believe you can translate the requirement to maximal AM modulation index.