FM Modulation-fm deviation

[kulabujji]

Hi, i am working on transmitters with fm modulation. in signal generators internal fm modulaion we are selected the fm deviation as KHz and MHz. but when we are applying the modulation externally from signal generator fm deviation in dBm. what is the difference beteen these two? please explain this

 

[biff44]

when you program, thru the front panel, a modern synthesizer, you set up the deviation and the modulating frequency (what the internal modulating oscillator frequency is set to), like in +/- 1 KHz deviation at a 20 KHz rate.

If you externally set up FM modulation thru a front panel BNC connector, you set the external source at some frequency (the modulating frequency), and you vary the voltage you are applying to that BNC connector so that the deviation is proper. Once again, you would set up a Voltage so that the deviation is +/- 1 KHz and set the external oscillator to the 20 KHz rate.

They are the same, but set up a little differently.

 

[D.A.(Tony)Stewart]

Each FM generator has a different gain for each scale... Look for sensitivity of MHz per volt or KHz /Volt and then convert your dBm 50Ω to voltage from 1 milliwatt.=0dBm or measure it... dBm power to dBv voltage can be easily looked up or calculated. Also factor RMS vs Pk-pk in the conversion.

In FM-FM your SNR improvement factor is also measure in dB with the ratio of p-p deviation of carrier in KHz or MHz and the bandwidth of your signal and BW of your receiver should be matched...

 

[FvM]

People are using a thing called instrument manual to answer similar questions...

 

[D.A.(Tony)Stewart]

Yep, if its not intuitive Read the Fine Manual.