BCD325P2/BCD996P2: FM Or NFM

[CanesFan95]

How do we tell which one to use? If you're scanning 450 & 460 MHz stuff, then I guess it should be NFM since those are referred to as "narrowband" 12.5 kHz? But 440 ham should be FM, or WFM?

The "Easier to Read Manual" has a table that says if you use Auto, that it defaults to NFM for 440 ham. But I thought 440 was 25 kHz bandwidth, so shouldn't that be WFM? Or is it just FM?

See my confusion here? How do we nail this down and know exactly which one to use?

 

[nd5y]

There is no way to tell for sure except to actually measure the transmit deviation with a service monitor.

WFM is 200 kHz bandwidth/75 kHz deviation.
FM is 16 to 20 kHz bandwidth/4 to 5 kHz deviation.
NFM is 12.5 kHz bandwidth/2.5 kHz deviation.

There is very little difference between FM and NFM settings on most scanners. It's not enough to prevent you from hearing something. They usually only have one IF filter bandwidth (25-30 kHz or so) and just change the receive audio level. If you don't know what to use then use FM and change it to NFM if the audio level seems low.

Almost all business, public safety and federal government analog stuff between 138-470 MHz is NFM now.

This article explains who had to change from FM to NFM in 2013. Federal users had to change before 2008.
https://wiki.radioreference.com/index.php/Narrowbanding.

Almost all amateur VHF/UHF repeaters are FM. Very few ham systems are NFM.

88-108 MHz FM broadcast band is WFM. You won't be able to receive that if set to FM or NFM and you might not be able to receive FM or NFM signals if set to WFM because of the 200 kHz bandwidth filters required for WFM.

 

[CanesFan95]

Great post !

 

[hiegtx]

Great post !

Don't forget that on the 436HP & 536HP, you can set the band defaults (FM or NFM), as well as the step sixe on the Band Defaults tab in the Profile Editor.

 

[ChrisABQ]

I have noticed, FM signals travel a small amount of distance further than NFM (because it's a bit wider banded) and the audio level of NFM is a bit louder than FM.

 

[Ubbe]

FM is louder than NFM and to compensate for that in scanners the audio amplification are increased when NFM is selected.

The carrier power are the same, and coverage, regardless if NFM, FM or WFM is used.
It is a less noise/signal ratio with NFM and has a bigger background hiss at weaker signal levels.

Most scanners ( all?) have a narrower filter to switch in when selecting NFM mode.

Where I live most amateur analog repeaters on VHF are NFM and UHF are FM modulated.

/Ubbe

 

[ChrisABQ]

Another instance where we could argue all day. I did start the sentence with "I have noticed". This has been my experience since I got back into scanning 2 years ago. I have had to increase the volume adjustment on FM to compensate so it's the same audio levels as other NFM channels. Have a nice day.