Frequency Modulation

[t.man]

how can one determine the frequency deviation from the frequency-modulated carrier displayed on a 'scope?

am i right to say modulation index(mi) = frequency deviation/modulating frequency?

 

[flat5]

Some info
Frequency Modulation

 

[audioguru]

Full modulation of an FM broadcast station is only 75kHz. Since the carrier is at such a high frequency of around 100mHz then you won't see the tiny amount of frequency deviation on an oscilloscope.

 

[flat5]

There is a 'scope technique where you use both hoz. & vert. inputs. You end up with a Bezel function or Lazarus function...
I sometimes used it at work 30 years ago and can't remember the details.

 

[JimB]

how can one determine the frequency deviation from the frequency-modulated carrier displayed on a 'scope?

Have a look at this link:
https://www.electro-tech-online.com/custompdfs/2009/01/HartfordModulation.pdf
There is a procedure in there for measuring deviation using a scope.
Be aware however, that the deviation must be a significant percentage of the carrier frequency before this technique is viable.

am i right to say modulation index(mi) = frequency deviation/modulating frequency?

Yes.

JimB