FM vs FMN

[altec]

Hi, I was monitoring the frequency of 155.8425 and am not sure if its FM or FMN. I'm not really familar what the difference is or what they both mean but seem to come in clear set on either one. I think if the frequency would be 155.840 or 155.845 it would be set under FM but I noticed most VHF frequencies with a odd ball number in the database are set to FMN. The true freq is 155.8425 and still come in with no difference in signal on 155.840 or 155.845. Also does this apply to UHF frequencies too?

 

[n4yek]

All newer radios made today use less frequency deviation than radios made years ago. This is done to better utilize the spectrum because of over crowding. It is very noticeable when you come across a transmission that has very low audio, less deviation, than older units that sound extremely loud when they talk. One thing you will notice, if you have your deviation set to NFM and the audio sound a little distorted, you can set it to FM and it will sound much better. NFM is I believe 6 to 12 KHz wide and FM is 25 KHz wide. (someone correct me if I am incorrect on that)
This will apply no matter what frequency band you use, from low band to 800 MHz.
It also helps a bunch when listening to digital, conventional frequencies to set your deviation to FM, it helps the scanner to decode the audio easier.
A frequency of 155.8425 will most likely be FMN, a frequency of 154.310 can be both.
It can be confusing on a subject like this, but suffice it to say anything new will be NFM.

 

[daedalus]

But to make it simple -

Broadcast FM (and I think TV audio) is Wideband FM, generally called FM. 99.9% of everything else (in the US) is Narrowband FM, usually abreviated NFM.

 

[kb2vxa]

OK, a bit of history. WFM was 30KHz deviation which was halved to 15KHZ and called NFM.

Fast forward; on today's scanners standard FM and TV broadcast is called WFM, the old 15KHz standard is now called FM and since it was halved again the new standard is NFM. Since "FM" has been phased out for the most part you may as well program all channels for NFM and if one is clipped and distorted reprogram it for FM until you notice a loss of volume when they make the conversion and they will soon enough.

Don't let the four digit "split channels" confuse you, toss the band plan out the window. Most if not all standard assignments in any given area are now also NFM allowing room for the splits.