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GMRS / FRS Discussions related to GMRS (General Mobile Radio Service) and FRS (Family Radio Service) communications

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Old 01-20-2013, 12:01 PM
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i was wondering if someone could answer a few questions... im trying to program a radio to the frs gmrs band. what is the freq step for these channels as well as what is the proper band wb or nb. what will happen if any of these were programmed incorrecly,
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Old 01-20-2013, 3:04 PM
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FRS is 12.5 Narrow and GMRS is 25 wide
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Last edited by spd640; 01-20-2013 at 3:06 PM..
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Old 01-20-2013, 3:34 PM
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Quote:
Originally Posted by billdozer View Post
i was wondering if someone could answer a few questions... im trying to program a radio to the frs gmrs band. what is the freq step for these channels as well as what is the proper band wb or nb. what will happen if any of these were programmed incorrecly,
The bandwidth determines the frequency step. For this discussion, NB is 12.5 KHz while WB is 25 KHz.

WB and NB can talk to each other, but how well depends on a lot of variables. Since you'll likely be talking with others, you'll want to program your radios to match the bandwith per service.

Just keep in mind that FRS has a max power limit of .5 watts on all 14 frequencies. GMRS licensees can run up to 5 watts on FRS 1 to 7 which are shared with GMRS. Different rules apply to the 8 GMRS only frequency pairs.
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Old 01-20-2013, 4:42 PM
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Thanks for the responses. so if im running nb i need the freq step at 12.5 and wb is 25? why are there other options like 2.5 and so on? i also plan to use the radio on public saftey bands. I just dont comprehend the frequency steps thing. im running fire freq of 154.14500 with a pl code.. i have radio on wb and the freq step is 2.5. for some reason my radio out preformes our $1000 motorolas using my current settings. our motorolas are nb and i think either 25 or 12.5 steps. Can someone clear that up
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Old 01-22-2013, 12:04 PM
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Thanks for the responses. so if im running nb i need the freq step at 12.5 and wb is 25? why are there other options like 2.5 and so on? i also plan to use the radio on public saftey bands. I just dont comprehend the frequency steps thing. im running fire freq of 154.14500 with a pl code.. i have radio on wb and the freq step is 2.5. for some reason my radio out preformes our $1000 motorolas using my current settings. our motorolas are nb and i think either 25 or 12.5 steps. Can someone clear that up
You're confusing tuning steps with bandwidth. Your radio probably has a setting for "narrow". That's what you select for use in the united states now unless you're on the ham band, marine or GMRS. FRS is narrow
It also sounds like you're probably using some chinese ham toy. You might want to check to see if its certified to operate in the radio services you want to transmit in.

Last edited by rapidcharger; 01-22-2013 at 12:17 PM..
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Old 01-22-2013, 4:05 PM
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Narrowband: spacing = 12.5 kHz; max. deviation = +/- 2.5 kHz; occupation = ~ 11 kHz.

Wideband: spacing = 25 kHz (usually); max. deviation = +/- 5.0 kHz; occupation =~ 16 kHz.

Radio programming packages are not consistent in how they denominate narrowband and wideband: some do it in terms of max. deviation and some do it in terms of channel spacing. The latter is more correct technically, but using the rules of thumb above, it all comes out in the wash.
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Old 01-22-2013, 4:47 PM
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i am running a chinese toy... baofeng uv5r.. i have settings for step and shf deviation.. I know were narrow band now, but lets say for my learning sake that im running wide band on freq. 154.14500. im running a step of 2.5 shft dev is off. is this set up correct.. i know you said wb is 25 but if i program that step with my freq it dont accept it and the freq displays a lower freq.. the system is a simplex with a pl code.. i have the pl right and i did a radio check with those settings (as an experiment) and my radio went into dispatch clear at about 15 air miles away. our depts 1k dollar motorolas cant even do that... Just wondering why i can do this with these settings and why it wont accept the freq with the step set to 25 in wb.. sorry for the fuss but im starting to get more into the workings of radios and want to know this stuff.

also curious as to why a dual band radio only allows you the choice of one step for all channels and not a step size for each channel.. i know im beating a dead horse here sorry but i really am interested in learning more.
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Old 01-22-2013, 9:46 PM
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"Step" is not, as your question implies, synonymous with "channel spacing" in this context.

Rather, it has to do with how the CPU defines frequency for the synthesizer. Chips cannot deal natively with floating point numbers, only integers. So a frequency is defined as X number of "steps" (of a pre-defined offset) from a base frequency.

A totally hypothetical example for purposes of illustration:

If your frequency of interest were 460.025, then with a base of 460 and a step of .025, the frequency would be represented by the chip as the integer "1". If the base were 460 and the step were .0125, the frequency would be represented by the integer "2." And so forth.

That is why "step" has to be set on a per radio basis.

Offhand, I have no idea what "shft dev" means (assuming it means anything other than max. deviation).
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Old 01-22-2013, 10:43 PM
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Shf dev is shift deviation. Repeater offset. How far the radio shifts frequency. There will be another menu in that radio for shift direction.
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