Ham Repeaters - use FM or NFM on TRX-1

[jackmail226]

For TRX-1 can anyone let me know which type of FM to program for best reception of 2 meter and 70cm Ham Repeaters. Is it FM or NFM. I've read elsewhere that NFM will detect and let you hear weaker signals. Any suggestions appreciated.

 

[Ace9133uwu]

I’ve always programmed NFM for 2 Meter & 70CM ham on my scanners. It definitely does help increase reception.

 

[nd5y]

Almost all ham repeaters are FM (5 kHz deviation) not NFM (2.5 kHz deviation).

 

[mmckenna]

NFM may work, but since most 2 meter and 70cm repeaters are wide FM, the audio will sound distorted.

There are some NFM ham repeaters out there, but they are pretty rare.

You may hear more NFM on the 900MHz band as a lot of that commercial gear was NFM originally.


Essentially, try both and see how it sounds. You'll likely find that wide FM (5KHz deviation, 25KHz channel width) is going to sound better.

 

[jackmail226]

Thanks very much for the help

 

[Ubbe]

If a FM signal are fully modulated at 5KHz and a NFM fully at 2,5KHz then if both have the same RF signal strength the FM one will have less noise. It's more difficult to design a squelch system that handles both FM and NFM as NFM have a less signal/noise ratio, more noise in the signal compared to FM and needs two different squelch settings.

But if you listen to a 2,5Khz modulated signal in FM mode then you'll need to increase the volume as it will sound weak and that also includes increasing the background noise. So in that case it might be better to use NFM mode. It will probably depend of the quality of the receiver design if one setting will be better than the other. A scanner like SDS100 that have DSP demodulator have a considerable amount of modulation noise when the signal are modulated at a nominal level, like a data signal, then the FM setting to receive a NFM signal will produce less noise, something that UPman used to recommend to improve reception.

/Ubbe

 

[MStep]

I must be getting too old for this hobby. When I came into the hobby many moons ago, the differentiation was that FM, (sometimes referred to as FMW, or Wide), was used for the FM broadcast band (88 - 108 MHz in the USA), and FMN, or Narrow, was used for communications frequencies like police, fire, etc. But that may not be technically correct any longer as terminology has changed over the years and receiver technology has evolved. So as some may suggest, it doesn't cost anything to experiment to see which configuration works best for you. Fortunately most receivers allow you to lock in the mode on a per-channel basis.

 

[mmckenna]

In the two way radio industry, especially the last 25-30 years, FM Narrow was 2.5KHz deviation/12.5KHz channel width. FM Wide was 5KHz deviation/25KHz channels (not to mention the 4KHz/20KHz stuff if you want to really confuse people). Go back a few decades and you'd find 30KHz channels, 50KHz channels, etc.

Since 2 way radio and broadcast were different industries, it was dependent on where you worked or which part of the hobby you were in.

Now, we're dealing with digital, and having 25KHz, 12.5KHz and 6.25KHz channel width starts to play in, so the "wide/narrow" thing starts to get confusing, since it entirely depends on what kind of system one is talking about.

Maybe someday the scanner manufacturer(s) will catch up and start doing things by deviation or channel width using numbers rather than what can be regarded as an arbitrary word.