NFM vs FM

[gas]

Being new to the whole radio hobby, i discovered last night that if i change the frequency modulation from NFM to FM on my 996t the reception is much clearer on nearly all of my frequencies? (less background hissing) Can someone offer an explaination for this? What is the difference between NFM and FM?

 

[crayon]

http://wiki.radioreference.com/index.php/NFM

 

[gas]

well according to this i'd be better off leaving it on NFM - I think? It says most systems now use NFM, but i still don't understand why my receptions are clearer on FM?
(call me scott - scott no idea)!

 

[crayon]

but i still don't understand why my receptions are clearer on FM

Because as the wiki pointed out, FM on most scanners is really NFM and NFM on most scanners is really SNFM.

Does that help?

NFM - Narrowband FM (called FM on most scanners)
SNFM - Super-Narrowband FM (called NFM on most scanners)

 

[crayon]

The concept of bandwidith might also be eluding you ...

FM has a wider bandwidth than NFM. When you set your scanner to NFM and you receive an FM signal .. what you are really doing is trying to do, electronically, is squeeze a fat signal through a narrow hole.

 

[bc780l]

For our purposes:
FM = 5kHz deviation
NFM = 2.5kHz deviation

NFM is becoming, and soon will be the base standard. RR database is not accurately listing FM vs. NFM for most areas, so you either have to look at the actual license (if the techs are setting the radios up properly for the license) or trial by error. Some receivers will give you a boost with NFM because of the lower deviation containing the signal intelligence, thus it may sound louder. If, however, it's really an FM channel, you may hear a lot of clipping.

 

[gas]

For our purposes:
FM = 5kHz deviation
NFM = 2.5kHz deviation

NFM is becoming, and soon will be the base standard. RR database is not accurately listing FM vs. NFM for most areas, so you either have to look at the actual license (if the techs are setting the radios up properly for the license) or trial by error. Some receivers will give you a boost with NFM because of the lower deviation containing the signal intelligence, thus it may sound louder. If, however, it's really an FM channel, you may hear a lot of clipping.

Thank you..

 

[gas]

The concept of bandwidith might also be eluding you ...

FM has a wider bandwidth than NFM. When you set your scanner to NFM and you receive an FM signal .. what you are really doing is trying to do, electronically, is squeeze a fat signal through a narrow hole.

Thanks champ - the penny has dropped! and yeah your right bc701 since going to FM a lot of clipping has dropped, it seems to be much clearer..

 

[FlashP]

Narrow, but which part?

Narrow band on the transmitter side is a bit simpler than narrow band on the scanner. The lower deviation requires a change in the audio processing - otherwise the voices will sound too quiet compared to 'wider' deviation channels. The receiver can also take advantage of the narrower RF signal by using tighter filters, reducing adjacent channel interference etc.

My impression is that most scanners use the FM vs NFM setting to change the audio, but they still use the same RF filters. Certainly, my 996 will receive "narrow" FM signals on the true frequency as well as the +7.5 kHz and -7.5 kHz adjacent channels, no matter which setting I choose.

Flash

 

[SCPD]

Narrow Band

ok so the USFS and NP radios have gone to Narrow Band so should I use NFM or FM on my scanner for the best signal?

 

[UPMan]

NFM for the best audio balance with other channels.