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Non Standard Repeater Offsets


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#1 Lscott

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Posted 14 September 2020 - 08:39 AM

Looking through the FCC rules there doesn't seem to be any requirements that repeater offsets must be 5MHz.

 

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§95.1763   GMRS channels.

The GMRS is allotted 30 channels—16 main channels and 14 interstitial channels. GMRS stations may transmit on any of the channels as indicated below.

(a) 462 MHz main channels. Only mobile, hand-held portable, repeater, base and fixed stations may transmit on these 8 channels. The channel center frequencies are: 462.5500, 462.5750, 462.6000, 462.6250, 462.6500, 462.6750, 462.7000, and 462.7250 MHz.

(B) 462 MHz interstitial channels. Only mobile, hand-held portable and base stations may transmit on these 7 channels. The channel center frequencies are: 462.5625, 462.5875, 462.6125, 462.6375, 462.6625, 462.6875, and 462.7125 MHz.

© 467 MHz main channels. Only mobile, hand-held portable, control and fixed stations may transmit on these 8 channels. Mobile, hand-held portable and control stations may transmit on these channels only when communicating through a repeater station or making brief test transmissions in accordance with §95.319©. The channel center frequencies are: 467.5500, 467.5750, 467.6000, 467.6250, 467.6500, 467.6750, 467.7000, and 467.7250 MHz.

(d) 467 MHz interstitial channels. Only hand-held portable units may transmit on these 7 channels. The channel center frequencies are: 467.5675, 467.5875, 467.6125, 467.6375, 467.6625, 467.6875, and 467.7125 MHz.

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I see a lot of newbie questions about repeaters where the "typical" reply states the repeater input frequency is 5MHz higher than the output frequency. However the rules don't require that. Read sections §95.1763 A and C. No mention about a required offset when going through a repeater. It seems so long as the repeater output frequency is one of the 462MHz main channels and the input frequency is one of the 467MHz main channels the FCC is fine with that.

 

Why does that matter?

 

Many people are buying GMRS specific radios that have the repeater frequencies per-programmed into them, with the "common" 5MHz offset assumed by the manufacture and hard coded by the firmware. However if a repeater owner sets up his system to use an input frequency and output frequency that is NOT a 5MHz offset anyone unfortunate enough to own a radio with the repeater frequencies hard coded by the firmware is out of luck. There is noway to make it work short of changing the frequencies.

 

For somebody who wants to keep his repeater "private" with reduced chances of being abused by non authorized users could employ a nonstandard frequency offset. Of course anyone who wishes to use the repeater must have a radio that allows the "non-standard" 5MHz offset to be programmed into it. That leaves for the most part old commercial radios.

 

For a really flexible GMRS specific radio a manufacture should provide a repeater memory channel where the input and output frequencies are selected from a list along with the access tone(s) required.

 

I see enough comments about the Midland radios concerning the tone and bandwidth issues, but nothing about the repeater offsets. If the radios are targeted to be "fully" GMRS rule compliant, sooner or later, the above issue should be addressed as well. This likely also applies to the other GMRS specific radios I see mentioned on the forum.  


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#2 kb2ztx

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Posted 14 September 2020 - 01:21 PM

I guess i have been in the LMR world way too long but i dont think i have ever seen a UHF repeater that did not use 5mhz. That is the standard in LMR and most licenses will show that. I agree its not spelled out in GMRS rules but I can't imagine anyone who would use different output and input frequencies as you described. Even in the Ham world most all UHF repeaters are 5mhz apart. I dont see a need for commercial providers to make a radio to be able to use anything other than 5mhz. JMHO


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#3 axorlov

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Posted 14 September 2020 - 03:13 PM

I remember discussion of this topic on this board before the rule change in 2017. The gist was the same. For LMR +5MHz offset is mandated, but for GMRS there is nothing in the rules to clearly prohibit non-5MHz offset.

 

It's impolite. If you use non-standard offset you are tying up two [commonly recognized] repeater channels instead of one. Now two guys, instead of one, are angry at you for the interference. If you do this in rural setting on your ranch, or in the woods, probably nobody would care. 


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- Alex


#4 Lscott

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Posted 14 September 2020 - 05:05 PM

I dont see a need for commercial providers to make a radio to be able to use anything other than 5mhz. JMHO

Perhaps.

 

Given the recent rule changes GMRS repeaters have to tolerate possible interference on the adjacent interstitial frequencies between the main repeater input frequencies, if not on the frequencies used. There have been a few comments on the forum about this. If the offending person or business is not willing to change the repeater owner may have little choice.

 

In my case a repeater, about the only one around in the area, has one or more local families sitting on the repeater output frequency. Fat chance getting them to move given the little kids are always screwing with the radios don't understand what is going on and the parents don't care. Several other channels are used by local businesses including, I suspect, by a nearby Chrysler assembly plant based on what I hear being discussed.   


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#5 kb2ztx

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Posted 15 September 2020 - 05:27 AM

So guess im confused by your statement. If the kids are on the output what harm is it to change input output at the same time ? When i was in NY there were lots of places that used GMRS outputs. I had PL/DPL on my repeater and unless i was in CSQ mode it didn't bother me. A repeater on the mountain normally worked better than a bubble pack radio in a store on my mobile. We are stuck with few channels. Taking one pair and using them shouldn't make us need to split between pairs. I guess there could be a case for it but nothing you mentioned is. If your re tuning a duplexor due to users on that output why not just change the input at the same time. 



#6 mbrun

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Posted 15 September 2020 - 06:56 AM

LScott, I appreciate you bringing this point to life. Having given it some thought, I am landing on the “Just because you could, does no mean you should” position. Some things settle out in time as “It is just good practice”. Why, because in time users determine that certain practices contribute to the best mix of mix of value. Just like there is value in the FCC rule which defines the center frequencies that must be used. Imagine the value of GMRS if a users could choose their center frequency within the GMRS spectrum. How friendly and useful would that be? The uncoordinated and inconsistent use of frequencies would lead to the death, not growth, of GMRS.

In the amateur radio world, 5MHz offset are not mandated either, but after 100 years +/- Hams have settled on 5MHz as their best practice. Does not mean they can’t do something different?

Each variable that gets thrown into the mix for using a radio makes it more difficult for more and more people and therefore increases the barrier to entry and persistence.

As a systems engineer I personally have done a lot of things that were technically correct and very feasible, but in the end they contributed to reduced value for client. Less value because it made the system more difficult to understand, use and maintain and contributed little material to ultimate user. Just because you can, doesn’t mean you should.

Regards,

Michael
WRSH965


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#7 Lscott

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Posted 15 September 2020 - 08:39 AM

Taking one pair and using them shouldn't make us need to split between pairs. I guess there could be a case for it but nothing you mentioned is.

Splitting pairs would be an effective method to keep the majority of unauthorized users off a "private repeater", and most are - at least listed as such, given the current crop of GMRS specific radios can't handle this with the fixed 5MHz offset built into the firmware. Not publishing the access tones, or changing them, is a waste of time since some radios, particularly Ham, can automatically scan for them. And if the radio can't scan for the analog tone then trying one at a time Ker-chucking the repeater until they hear the squelch tail works too. The digital codes would take a bit more work. It wouldn't take long for somebody to figure out what they are and back to using the repeater.

 

As I pointed out earlier any users of a non-standard repeater offset system would likely need to use old Part 90 radios, or dual Part 90/95 certified radios, to use it. If somebody has the technical skill to build a repeater they likely have the skills to program the old radios to work on it.

 

Now the argument can be made that people can buy cheap radios, like the ubiquitous Baofangs and their derivatives, which can be programmed to work on such a system. However the majority of users simply want a radio they can turn on and communicate. They don't want to be radio tech geeks. I see enough posts on the forum from users who have problems just figuring out how to program the GMRS specific radios being sold where most of the technical settings are already set in the firmware.



#8 Lscott

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Posted 15 September 2020 - 08:49 AM

Very interesting comments from everybody. The ones about "it's good practice" are well taken and valid. As mentioned sticking to the 5MHz offset is a good idea, but not required by the FCC rules. If and when a case arises where using a non-standard repeater offset is justified the current crop of GMRS specific radios can't handle it. A point that a potential buyer should be aware of if they have this situation.



#9 JohnE

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Posted 15 September 2020 - 06:08 PM

 

Splitting pairs would be an effective method to keep the majority of unauthorized users off a "private repeater",

there are other methods to achieve this w/o resorting to moving the splits.


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#10 marcspaz

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Posted 15 September 2020 - 10:16 PM

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#11 Lscott

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Posted 16 September 2020 - 09:31 AM

there are other methods to achieve this w/o resorting to moving the splits.

I'm sure there are like adding a DTMF decoder to unlock the repeater, which re-locks after a period of inactivity. Another is some of the 2-tone, 5-tone and digital ANI access systems supported by many of the commercial grade radios. I mentioned in another post where a Ham switched his Ham repeater to using Motorola MDC-1200 for access control too.

 

Oh, I have a couple of Kenwood TK-2360 16 channel VHF radios that can do MDC-1200. I would like to find used some of the Kenwood TK-3360 UHF versions with the rare 400-470 MHz frequency range to add to my HT collection.



#12 marcspaz

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Posted 16 September 2020 - 10:03 AM

In the Amateur Radio world, all offsets that are commonly used and considered best practice, have come out of a developed band plan.  The band plan dictates what the offsets (frequency pairs) are for coordination, to help prevent harmful interference with other repeaters and other services inside of those allocated spaces.  The American Radio Relay League defines the band plan as "a voluntary division of a band to avoid interference between incompatible modes."

 

Does anyone know if something similar exists for GMRS and its repeater offsets?  Tradition seems like a good answer, but I have to think there is more to it than that.

 

Also, using non-standard pairs would likely end up causing interference for others who are using the standard +5 in a GMRS dense area like where I am.  There are repeaters around my house on every available (standard) pair, with some overlap with several machines, that only have PL tones separating which machine you bring up. 

 

You would also break the repeater capability for every repeater capable type approved radio on the market.  The FCC issued a PDF as guidance to the makers to help ensure devices meet the type acceptance criteria, and that document shows the +5MHz offsets.  While it may not be codified in the rules, based on the document, I am pretty sure that +5MHz is what's expected by the FCC, too.


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#13 Lscott

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Posted 16 September 2020 - 12:55 PM

 While it may not be codified in the rules, based on the document, I am pretty sure that +5MHz is what's expected by the FCC, too.

 

Maybe at some point they will issue a rule change which specifically requires it and end the debate. 8-) Until then there is some wiggle room.

 

Even in the Ham world standard offsets are not always used. The following is for a 2M machine out where a Ham buddy lives.

 

 https://www.repeater..._id=26&ID=10560

 

The "standard" for the 2M band is 0.6MHz. But not in the above case and it is a coordinated repeater, apparently, as you'll notice towards the bottom of the page.

 

https://wiki.radiore...ndex.php/Offset

 

In the early days Hams used converted commercial VHF and UHF repeaters. On UHF the 5 MHz offset, I think, was mostly to do with the technical limitations on the cavity filters used.

 

Here is some interesting reading on another forum.

 

https://forums.qrz.c...r-splits.26321/






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