National GMRS DataBase question...

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hpycmpr

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The quick answer is that band is already narrow banded. GMRS channels are 25 kHz apart. In between those channels are the FRS radio channels. Together they are 12.5 kHz apart.

Steve
 

lbfd09

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The quick answer is that band is already narrow banded. GMRS channels are 25 kHz apart. In between those channels are the FRS radio channels. Together they are 12.5 kHz apart.

Steve
Okay - keeping in mind that bandwidth is not channel spacing - next question is when did this happen? I do recall when the splinter channels were added as low power channels as not to interfere with GMRS repeater and established communications. When this happened no mention to narrowband this user group was made. rather the previous explanation was given at that time.

I am guessing the emission type for GMRS back then was 20K0F3E and then changed to 11K2F3E? I am not in GMRS and only listen to this group of users. I am observing most of my scanner stops will display FM and not NFM.

In looking at FCC Part95a - "95.629 (a)....The authorized bandwidth for emission type F1D, G1D, F3E or G3E is 20 kHz." Or is this an outdated citation?

Thanks for your insight.
 
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hpycmpr

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You got me digging deeper.

The narrow band rules apply only to FCC Rules Part 90 users i.e. Public Safety and Industrial/Business users in the VHF high band and the UHF 450-512 MHz band.

Other users including Part 95 (GMRS, FRS,CB, etc) are not affected. Having said that I found that the authorized bandwidth for FRS is 12.5 kHz, while GMRS is 20 kHz. (95.633)

My GRE 500/600 does not indicate whether the received signal is NFM - only if it's FM or Digital. Does your unit indicate NFM/FM?

Steve
 

kruser

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Correct me if I'm wrong but I do not think any currently available scanner can discern between a narrow and normal FM signal. They are only going to display the mode you set them too when you set your search parameters.
 
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UPMan

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That is correct. All the receiver knows is the modulation deviation, not the maximum. So, someone speaking at normal modulation on NFM and someone speaking quietly (i.e. undermodulating) on FM could have the same modulation deviation...the receiver cannot tell based on the signal that the 2nd signal is not just an NFM signal.
 

lbfd09

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My Pro-197 does display NFM when in auto mode for the local town, county fire, and USFS frequencies. I'll admit I have NO idea how GRE does that, but it does seem to work. (Just now getting the hang of the more techy side of NFM vs FM.)

Back to the original question - I see my suspicions were confirmed above. Can we see a correction in the DataBase regarding this? Or does this need to be submitted via a different channel?
 

hpycmpr

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By the way your original post, second link comes up as "invalid agency ID" for me.
Steve

I suspect the question mark did it.
 
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UPMan

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It is because "AUTO = "lookup the default setting for the band" and for that band, the default is NFM.
 

UPMan

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Oh, and if the Description in the dB could be fixed at the same time ... (I'd submit it on the dB submissions page, but it would be a duplicate submission)
 

kruser

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It is because "AUTO = "lookup the default setting for the band" and for that band, the default is NFM.
Correct! Thanks Paul for explaining that one!

Another example is if you set a frequency of say 126.5000. And then you set the modulation type to AUTO, the scanner will not listen to the signal first to determine the modulation type (that would take time), it is going to check its own internal tables and see that 126.5000 falls within an AM band so AM is what you will get even if an FM signal popped up on that frequency. Many manufacturers will list specs for the scanner and those specs will usually show the default mode (am, fm, nfm etc..) for each band segment. What is listed in those specs is the mode your scanner will use if you leave the modulation type set to auto. I suppose setting the correct mode may speed up scanning some but I imagine it's real purpose is to override the bands default for signals that do not use the default mode.
From what UPMan said in his earlier post, I'd think if a radio was going to attempt to determine the mode, it would need to sample the audio for several seconds before it could make a half assed guess. With the short duration of most comms on a scanner, I doubt it would ever work plus you would miss about everything while the thing was trying to figure out the mode.
So in a nutshell, the "Auto" setting does not work like you are thinking it does. I can see where that can be confusing for someone as auto usually means... well it means auto!
It's just not the same kind of auto if that makes any sense!
 
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