FM Mode Actually Used When Mode Is "AUTO" ?

[BOBRR]

Hello,
Have a 996, and using Butel's arc996 software for programming it.

Under "MODE," I have everything set to Auto.

But have been wondering about the three FM modes that are apparently available (WFM, FM, and NFM).

Is the radio truly smart enough to select which of the three is "correct" ?

I have read on the wiki that: " because as the wiki pointed out, FM on most scanners is really NFM and NFM on most scanners is really SNFM".

So, what is the radio really selecting when the mode is set to AUTO ?

Is the Default mode selected under AUTO really correct; it seems like it might not be per the wiki ?

Does it pay to play with each fm freq. to see which sounds best, or "does the radio really know best" which mode to use ?

Any clarifications on this would be most appreciated.

Thanks,
Bob

 

[KD4UXQ]

FM Modes

The radio is programmed in firmware to assume a particular FM mode according to the most common mode used for the frequency programmed. This is why you have the ability to chose becuase it won't always be correct.

There are 3 basic FM modes as relates to land mobile radios and scanners. WFM for music (75KHz) and TV, FM is the usual 5KHz deviation of land mobile radio and NFM (narrow FM) is the 2.5KHz deviation used on newer LMR systems because newer equipment can be precise enough to allow for stable carrier frequencies and narrow deviations. Narrow FM allows for closer channel spacing than FM at 5KHz deviation which allows for more channels in the same frequency range.

In land mobile radio the 2 basic deviations are usually referred to as FM and NFM, but compared to WFM on broadcast bands I suppose you could say that FM is a narrow FM and NFM comapred to WFM is a NNFM. But usually in land mobile radio they are just refered to as FM and NFM.

 

[KD4UXQ]

Auto

Auto should work just fine in most cases. If the radio selects FM (5KHz dev) and the transmitter being monitored is NFM (2.5KHz dev) it will sound fine except maybe a low volume. If the radio selects NFM (2.5KHz dev) and the transmitter is actually using FM (5KHZ dev) the audio may sound loud and distorted.

Also one other thing about AM. The 137-142 and 148-150 bands are assumed by the radio to be FM which is partly correct for US gov LMR when in fact they are sometimes used by military aircraft and then the mode is usually AM. This is also true for the 380-400 MHz portion of the 225-400 band. That area is used by US Gov LMR, but aircraft useage in that range is usually AM.

There are always exceptions. I am only interested in aircarft operations in the 225-400 MHZ band and the channel spacing is 25KHz so I have a custom search range set for AM and 25KHz steps in that band.