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What's the difference between NFM and WFM ?

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Aug 20, 2007
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wfm modulation

I've tried to understand it from some articles (google) - but it's still not so clear to me...
In other words, how can I (if I can...) change a circuit from NFM <>WFM?
Any example will be very appreciate.

nfm modulation

Hi in NFM the modulation index is very low, much lower than 1. and WideBand FM (WFM) the modulation index is much larger than 1. NFM is mainly used for speech communication systems like HAM radio's and police and other type of communication except airplane VHF communications, they use AM for a very good reason. NFM looks from a spectrum point of few much more like AM, if the index is low its impossible to see the difference between AM and NFM spectrum. This is not true for WFM they look completely different.

clarify wfm

Thank you very much for the explanation, and here is what I found on Google

As with other modulation indices, in FM this quantity indicates by how much the modulated variable varies around its unmodulated level. For FM, it relates to the variations in the frequency of the carrier signal

It makes me now confused: If I take a CCO stage and an Audio stage and try to modulate the CCO (connecting the Audio to a varicap) - what changes do I have to do in order to get a WFM or NFM output?
Thanks for your further help.

what is the difference betwen nfm and fm

For the Transmitter side its easy, make sure your frequency variation with the varicap is small. This can be done by using a small Audio signal on the varicap of take a caricap with a small capacitor value and hence change on the total LC network. Last is better since it will give a lower noise contribution by the varicap. Its also wise to filter any frequency above 4 KHz before you modulate since its making signal wider, and since you want NFM its main use is voice.
Receiver side is more complicated since all your IF filters need to match your input spectrum for best result. So take IF filters with 12 KHz BW.


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perbedaan wfm dengan nfm

Well, Thanks again, you really helped me a lot!
As I'm talking about a transmitter (It's NFM now), and as I need it to be as WFM as it can be, I understand that I have to amplify the Audio or change the Varicap.
What I'm trying to do is to change both frequency and modulation mode of a small transmitter working on the 123MHz band. It uses a 24.700MHz crystal, so it works on the 5th overtone. I'm trying to use a 16MHz crystal - but it's pushed to the 9th overtone (about 176MHz).
I haven't tried to do reverse engineering on this particular circuit, but from what I could see, it has 2 multiplying stages, but here is something that I cannot understand as well: supposing that the first stage is a "tripler" and the second stage a "doubler" I was supposed to get 23.7 x 6 = 142.2MHz, not 123MHz - and I'm almost sure it uses 2 stages... may you have any explanation on this?
By the way, placing the 16MHz crystal on the same circuit, the Audio is now VERY low.
Thank you for be so helping :)

what is nfm modulation

You can't make WFM with a crystal in overtone atleast not 5th or 9th overtone due to the fact that the crystal doesn't allow you to change the offset to much !. Xtal is only good for NFM

wfm very low audio

I'm sorry, my mistake...
The device I have works on WFM (I receive it perfectly with a converted FM receiver (an FM receiver converted to receive up to 125MHz). It certainly works on 123MHz. It certainly works with the 23.7MHz crystal very well, even on my Oscilloscope I don't see it as a perfect sinus, as there are 3 height amplitudes, and again 3 and so on. But on listening is perfect.
So - as you've helped me so much with the NFM-WFM questions, My last one (I hope...) is how do you think it's being done? I mean that it works on a total 5th overtone, this is what I understand from 23.7 X 5 = 123MHz. However it has two multiplier stages which look almost similar - as far as I can see. So, the only question I have is how it's achieved? I quote myself from the previous post:
I cannot understand as well: supposing that the first stage is a "tripler" and the second stage a "doubler" I was supposed to get 23.7 x 6 = 142.2MHz, not 123MHz - and I'm almost sure it uses 2 stages...
It'll clarify to me many things.
Thank you!

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