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GMRS wide band or narrow band
- Thread starter matt131
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N_Jay
Guest
All else being the same 25 KHz should give you 1.5 to 6 db improved signal to noise (range)
conve36
Member
Am I the only one confused by this answer?
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N_Jay
Guest
rescuecomm
Member
Cutting the modulation limiting diode in a CB (am) radio yields about the same sort of effect. The signal can be detected over high noise levels.
Bob
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N_Jay
Guest
Yes, I guess it does if you don't consider the differences between AM and FM modulation. :wink:
rescuecomm
Member
Perhaps I should have included the phrase: "In lay terms."
Bob
Hello.
Narrow banding is just that, putting a signal in a narrower "channel".
All things being equal, a 25kHz wide signal will have better coverage.
And, clipping the modulation limiting diode in a CB can easily cause over modulation, a louder signal but less range.
In AM the ideal is around 80 to 90% modulation.
Anything over and the signal splatters.
But if we reduce the carrier and part of one sideband we have a signal that has all the components of a regular AM signal but far greater range.
From a range standpoint, CW is king with SSB being next and VSRC being next in line and than a tossup between AM and FM.
The big advantage FM has is the reduction of static noise.
Narrow banding is just that, putting a signal in a narrower "channel".
All things being equal, a 25kHz wide signal will have better coverage.
And, clipping the modulation limiting diode in a CB can easily cause over modulation, a louder signal but less range.
In AM the ideal is around 80 to 90% modulation.
Anything over and the signal splatters.
But if we reduce the carrier and part of one sideband we have a signal that has all the components of a regular AM signal but far greater range.
From a range standpoint, CW is king with SSB being next and VSRC being next in line and than a tossup between AM and FM.
The big advantage FM has is the reduction of static noise.
quarterwave
Member
Keep it wide band. You are not required to be narrow at this point, and your "coverage" will be better for the reasons others have explained above.
I am working on a project for my company modifying licenses and upgrading mobiles and MTR2000 repeaters to narrow. We expect a little less coverage, but given that we have Aux receivers, an extremely awesome main TX/RX site and a license for 300 watts / 500 ERP on VHF....I am going to have a hard time being able to tell if there is any difference. Mostly because I have no baseline. They haven't used this system for much besides data for a few years, but now the data has gone Cellular, and we are going to use the system for secondary/emergency backup on voice again. Our license is for 75mi radius....I have been told on 100 watts this thing was heard 150 miles out. I don't think I will have any range issues.
Not that you needed to know all that....but just to say that in a large system it may make no noticeable range difference to the end users with good equipment. Now, on the other hand, I operate 2 low profile 50 watt GMRS repeaters, and I can see where narrow banding them would reduce my range, especially with portables. If GMRS ever has to narrow band, I am just going to get a commercial license for my needs, and put up a TRBO repeater at a better site.
When we typically say "wide" band, it means 25khz right?
While GMRS frequencies are 25khz apart, the NEAREST assigned frequencies to GMRS are 12.5khz apart?
So would that make GMRS narrowband already?
For example
FRS CH 1 462.5625
GMRS CH 2 462.575
FRS CH 2 462.5875
While GMRS frequencies are 25khz apart, the NEAREST assigned frequencies to GMRS are 12.5khz apart?
So would that make GMRS narrowband already?
For example
FRS CH 1 462.5625
GMRS CH 2 462.575
FRS CH 2 462.5875
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N4KVE
Member
Here's the simple answer. Wideband is better. A wideband signal has up to 5 khz of deviation, while a narrowband signal can have no more than 2.5 khz deviation. GMRS is wideband, while FRS is narrowband. That's as simple as it gets.
cdesigns
Member
Ok I just got back into GMRS, and Im learning about the narrowband and other rules, my question is I have several FRS/GMRS bubble pack but expensive radios and they are WIDEBAND , how the FCC is going to regulate all those millions of GMRS radios already sold with wideband?
Im setting up a portable repeater to wideband because my bubble pack gmrs radios that are repeater capable will not work on narrowband with my repeater.
Im setting up a portable repeater to wideband because my bubble pack gmrs radios that are repeater capable will not work on narrowband with my repeater.
jhooten
Member
GMRS is a Part 95 service and not subject to the Part 90 narrow banding mandate.
W2NJS
Member
As Hooten just said, narrowbanding does not apply to GMRS. It also does not apply to hams, marine radio, NOAA weather broadcasts, the VHF paging channels, the UHF T-band, and MURS channels 4 and 5. Otherwise if you're a Part 90 licensee you must go to narrowband.
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prcguy
Member
Where does the 1.5 to 6dB come from? If the receiver IF BW is reduced proportionally for narrow band you will improve the S/N by 3dB in narrow band mode and range will be improved in narrow band.
Any time you reduce receiver IF BW you get this improvement and going from say a typical 15KHz IF BW on FM to 1.5KHz (narrow SSB or wide CW) will give you a 10dB S/N improvement, not counting any change in mode. Going four times narrower to 375Hz BW for CW will give you a whopping 16dB S/N improvement over the original 15KHz starting point.
prcguy
Any time you reduce receiver IF BW you get this improvement and going from say a typical 15KHz IF BW on FM to 1.5KHz (narrow SSB or wide CW) will give you a 10dB S/N improvement, not counting any change in mode. Going four times narrower to 375Hz BW for CW will give you a whopping 16dB S/N improvement over the original 15KHz starting point.
prcguy
WA0CBW
Member
It doesn't quite work that way. Your are mixing AM-FM-SSB-CW assuming they work the same. In an FM signal noise is noise is noise no matter what the IF bandwidth. As you narrow the signal the bandwidth decreases decreasing the signal to noise ratio reducing the received audio. Thus in FM reducing the bandwidth will reduce recovered audio in turn reducing the range from about 5 to 15% depending your conversion from db to percent. In our experience it seems to be about 10 to 20%.
BB
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rkraft
Member
Wideband vs Narrowband
There are a couple of advantages to Narrowband over Wideband:
1) You can put double the amount of repeaters, or stations, in a band of frequencies that uses Narrowband.
Just as an example, say you can put 100 repeater pairs in the repeater portion of the 2-meter band, currently. If you switch to Narrowband, you can pretty much double that amount to 200.
2) You won't increase your "range", BUT you will "DECREASE" your receiver signal to noise ratio! In other words, you pick up less noise.
However, the advantages of Wideband are:
1) The audio quality is much better! But that's only if your radio has a HI FI type receiver! Most two-way radios have a very limited audio frequency range (300-5000 Hz), which isn't music quality, but ok for simple voice. So basically, wideband operations has no other advantage over narrowband.
There are a couple of advantages to Narrowband over Wideband:
1) You can put double the amount of repeaters, or stations, in a band of frequencies that uses Narrowband.
Just as an example, say you can put 100 repeater pairs in the repeater portion of the 2-meter band, currently. If you switch to Narrowband, you can pretty much double that amount to 200.
2) You won't increase your "range", BUT you will "DECREASE" your receiver signal to noise ratio! In other words, you pick up less noise.
However, the advantages of Wideband are:
1) The audio quality is much better! But that's only if your radio has a HI FI type receiver! Most two-way radios have a very limited audio frequency range (300-5000 Hz), which isn't music quality, but ok for simple voice. So basically, wideband operations has no other advantage over narrowband.
In an ideal world this is true. But in the real world, one must take into consideration that the FRS channels are sandwiched between the GMRS channels. If you run wideband on GMRS, FRS users on adjacent channels will fall partly within your channel width, and they will interfere with you, and you will interfere with them. If you run narrowband, the FRS and GMRS channels no longer overlap, and you will get a lot less adjacent channel interference and crosstalk.
In a rural area where you are the only game in town, there are some advantages to running wideband on GMRS. But if there is a lot of RF congestion on the FRS channels, you're better off going narrow to eliminate bleedover from the FRS channels.
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