GMRS "Freq Pair"

[LakeMan2]

I had always thought (and read) that the GMRS repeater freq pair had to be exactly 5Mhz apart and therefore if the repeater was transmitting on 462.5500 then it must receive on 467.5500. I was reading through the part 95 doc and all it says is that you must use one 462 freq from the list and one 467 from from the list. It says nothing about them having to "match". If I am reading that correctly one could set up a repeater to receive on 467.7250 and transmit on 462.5500 and be perfectly legal. The benefit being possibly getting more isolation out of a duplexer with the slightly larger channel separation.

Am I missing something or is that correct?

 

[mmckenna]

Yes, that is correct. You -could- do that.

It would probably make you very unpopular if there were other GMRS users or GMRS repeaters in the area. Here's why:
You'd be tying up two frequency pairs.
One for your repeater input (say, 467.550)
One for your repeater output (say, 462.625)

That would make it difficult for nearby repeaters to use those two pairs (.550 and .625)
It would also make it difficult for you to monitor before transmitting.

And, it wouldn't really gain you anything useful, other than confusing other GMRS users, maybe keeping some of the riff raff off your system.

But, yeah, it could be done.

 

[Thunderknight]

The benefit being possibly getting more isolation out of a duplexer with the slightly larger channel separation.

I think the gain in isolation with that difference would be minimal, and possibly not even detectable.

 

[mmckenna]

I agree. Unless you had a really expensive duplexer, the 175KHz difference between the high and low end of GMRS wouldn't make much of a difference.

 

[rfradioconsult]

Depending on the design of your duplexer it could actually hurt your isolation. Some UHF duplexers are pass/reject with a notch 5 MHz from the pass frequency.

 

[LakeMan2]

I agree. I don't know that it is worth doing. I still found it interesting though that the using a matched freq pair (exactly 5MHz apart) is just a convention and not actually a requirement of the FCC. I am a big fan of having options, and this just means that, if needed, there are options that are still legal..

 

[RFI-EMI-GUY]

It would be a bad idea. What if another repeater is turned on using the pair that includes your input frequency? How would users on the other repeater be able to monitor activity of yours to avoid co channel interference?

 

[SCPD]

Not long ago I was asked to consult on a GMR system that was experiencing terrible interference. These friends had a beautiful mountain top location- But....shared with a number of other users-
Their line of sight distance exceeded 80 miles, perfect for any UHF user..... the problem was their repeater was right next to a 500 watt gas line company's 467.525Mhz remote. There was no way that moving the antenna or trying to notch out that 1/2 KW signal, would work- the GMRS'er were on the verge of abandoning the site and their system. After visiting the site and trying all my magic, I was going to concur that it was hopeless- But...
.
I re-read Part 95 ( 95.29 in particular, the section that deals with the channel usage) and it says nothing about which channel pairs are used for inputs and outputs. Having a sort of friendly business (like you would with your local Mafia Don) relationship with the FCC (as evidenced to anyone has read my previous posts) I called to my friendly, personnel Engineer-in-Charge.
.
"Can they invert the channel pairs?" I asked. (I figured they could but I wanted 'Their Words' on it)
.
The answer- As far as their office was concerned, that was fine- their was nothing in the regulations to prohibit it- in fact they could use any input-output channel configuration.
Re-programming their radios to use a 462MHz repeater in, 467 out, cured the problem. *
.
I got access to their system if I ever wanted it --- and a nice bottle wine......
.
.
* with digital encoded access to filter out any 462Mhz simplex activity

 

[hamptonbeach]

@LakeMan2 - that's EXACTLY the way I read the rules.

Thanks for the other replies that agreed, and yes I agree it may be an unpopular choice in an urban setting, but in rural areas that chances of interfering with anyone elses project would be slim.
I commented on someone elses post in the mygmrs.com forums that asked the exact same question, and I got vilified for my reply.
They all said over there (incorrectly - that the FCC rules were set in stone for a 5mhz offset.)
Now I feel better

 

[wyShack]

I am somewhat confused. when I read rule 95.29 b:

§ 95.29 Channels available.
(a) For a base station, fixed station, mobile station, or repeater station (a GMRS station that simultaneously retransmits the transmission of another GMRS station on a different channel or channels), the licensee of the GMRS system must select the transmitting channels or channel pairs (see§ 95.7(a) of this part) for the stations in the GMRS system from the following 462 MHz channels:


462.5500, 462.5750, 462.6000, 462.6250, 462.6500, 462.6750, 462.7000 and 462.7250.

(b) For a mobile station, control station, or fixed station operated in the duplex mode, the following 467 MHz channels may be used only to transmit communications through a repeater station and for remotely controlling a repeater station. The licensee of the GMRS system must select the transmitting channels or channel pairs (see§ 95.7(a) of this part) for the stations operated in the duplex mode, from the following 467 MHz channels:


467.5500, 467.5750, 467.6000, 467.6250, 467.6500, 467.6750, 467.7000 and 467.7250.

I am left with the impression that the 467 frequencies can only be used as repeater input(s). What am I missing?

 

[quarterwave]

You are not missing anything. You do use only the 467 for repeater inputs. The original post dealt with using a mis-matched pair....like 467.550 in and 462.725 out.

Someone threw in something about using a reversed pair, which everyone can debate the legalities of all day long, but that is not an accepted norm, rules or no rules.

 

[SCPD]

I am not a radio lawyer nor do I play one on TV, but if anyone re-reads WyShacks's post, a vebatim, quote of the Part 95 rule, they will see that the regulations say nothing about which pair, 462/467Mhz is to be used for the input and outputs. It only says that 467Mhz be use in a duplex arrangement (ie; "Repeater') and that if any remote control functions are included, they be on 467. Heck, the whole wording is very vague ("Poor") and by that interpretation, you could use a separate 467Mhz channel for your control functions. Remember too, that these are by definition, "Closed Systems"-- you are setting them up your own use. If you have guests, that is fine, but you set them up to your parameters, and hopefully any co-channel users can be accomodated. They are not for the convenience of the public-- they are not Ham repeaters.-- think ' Land Mobile Radio.'
My experience with GMRS is minimal, so I suggest anyone (like me) that would really want to know what is right or wrong do what I do at our labs---> Call the local FCC field office and ASK THEM. They are there to answer these very questions, and, despite their (I think undeserved) reputation, I have never found any BoogeyMen ready to pounce on me and haul my rear end into jail-- even when we have done something that went nasty.....
.
...........................................CF

 

[ecps92]

..well, not being a lawyer (but have slept at a Holiday Inn Express) it does and does quite well

For a base station, fixed station, mobile station, or repeater station = 462
For a mobile station, control station, or fixed station = 467

I am not a radio lawyer nor do I play one on TV, but if anyone re-reads WyShacks's post, a vebatim, quote of the Part 95 rule, they will see that the regulations say nothing about which pair, 462/467Mhz is to be used for the input and outputs. It only says that 467Mhz be use in a duplex arrangement (ie; "Repeater') and that if any remote control functions are included, they be on 467. Heck, by that interpretation, you could use a separate 467Mhz channel for your control functions. Simplex operations on 467 is a murky area, and I would not broach that subject, but I think anyone familiar with 2-way radio could see exceptions as to why it could be ok under various circumstance. My experience with GMRS is minimal, so I suggest anyone (like me) that would really want to know what is right or wrong do what I do at our labs --- Call the local FCC field office and ASK THEM. They are there to answer these very questions, and, despite their (I think undeserved) reputation, I have never found any BoogeyMen ready to pounce on me and haul my rear end into jail-- even when we have done something wrong.....
.
...........................................CF

 

[RFI-EMI-GUY]

I am somewhat confused. when I read rule 95.29 b:

§ 95.29 Channels available.
(a) For a base station, fixed station, mobile station, or repeater station (a GMRS station that simultaneously retransmits the transmission of another GMRS station on a different channel or channels), the licensee of the GMRS system must select the transmitting channels or channel pairs (see§ 95.7(a) of this part) for the stations in the GMRS system from the following 462 MHz channels:


462.5500, 462.5750, 462.6000, 462.6250, 462.6500, 462.6750, 462.7000 and 462.7250.

(b) For a mobile station, control station, or fixed station operated in the duplex mode, the following 467 MHz channels may be used only to transmit communications through a repeater station and for remotely controlling a repeater station. The licensee of the GMRS system must select the transmitting channels or channel pairs (see§ 95.7(a) of this part) for the stations operated in the duplex mode, from the following 467 MHz channels:


467.5500, 467.5750, 467.6000, 467.6250, 467.6500, 467.6750, 467.7000 and 467.7250.

I am left with the impression that the 467 frequencies can only be used as repeater input(s). What am I missing?

Thanks! Good find.

I see the reference to 95.7(a) does not clarify exactly what a "pair" is, so in theory you could have something other than exactly 5.000 MHz channel offset. It is clear that the 467 MHz channels are for repeater inputs. 95.7(b) sort of reinforces Coyote Frostbite's situation given that the field office "solved" her problem. Still I have to wonder why a utility remote terminal is permitted to be transmitting with all that power from a mountaintop.

I think we can all agree that the norm should be exact 5.000 MHz offsets and 467 MHz inputs. To deviate from that without reason in the uncoordinated world of GMRS is just asking for trouble later.

§ 95.7 Channel sharing.
(a) Channels or channel pairs (one 462 MHz frequency listed in § 95.29(a) of this part and one 467 MHz frequency listed in § 95.29(b) of this part) are available to GMRS systems only on a shared basis and will not be assigned for the exclusive use of any licensee. All station operators and GMRS system licensees must cooperate in the selection and use of channels to reduce interference and to make the most effective use of the facilities.

(b) Licensees of GMRS systems suffering or causing harmful interference are expected to cooperate and resolve this problem by mutually satisfactory arrangements. If the licensees are unable to do so, the FCC may impose restrictions including specifying the transmitter power, antenna height, or area or hours of operation of the stations concerned. Further, the use of any frequency at a given geographical location may be denied when, in the judgment of the FCC, its use in that location is not in the public interest; the use of any channel or channel pair may be restricted as to specified geographical areas, maximum power, or other operating conditions.
[48 FR 35237, Aug. 3, 1983, as amended at 53 FR 47715, Nov. 25, 1988; 63 FR 68974, Dec. 14, 1998; 64 FR 53241, Oct. 1, 1999]

 

[SCPD]

I added a few extra choice tidbits in editing, and reworded my last post a trifle (if it really makes any difference)....
.
I am not a radio lawyer nor do I play one on TV, but if anyone re-reads WyShacks's post, a vebatim, quote of the Part 95 rule, they will see that the regulations say nothing about which pair, 462/467Mhz is to be used for the input and outputs. It only says that 467Mhz be use in a duplex arrangement (ie; "Repeater') and that if any remote control functions are included, they be on 467. Heck, the whole wording is very vague ("Poor") and by that interpretation, you could use a separate 467Mhz channel for your control functions. Remember too, that these are by definition, "Closed Systems"-- you are setting them up your own use. If you have guests, that is fine, but you set them up to your parameters, and hopefully any co-channel users can be accomodated. They are not for the convenience of the public-- they are not Ham repeaters.-- think ' Land Mobile Radio.'
My experience with GMRS is minimal, so I suggest anyone (like me) that would really want to know what is right or wrong do what I do at our labs---> Call the local FCC field office and ASK THEM. They are there to answer these very questions, and, despite their (I think undeserved) reputation, I have never found any BoogeyMen ready to pounce on me and haul my rear end into jail-- even when we have done something that went nasty.....
.
Ok, I'm Finally! done- off to lunch
.
...........................................CF

 

[DaveNF2G]

I am not a radio lawyer nor do I play one on TV, but if anyone re-reads WyShacks's post, a vebatim, quote of the Part 95 rule, they will see that the regulations say nothing about which pair, 462/467Mhz is to be used for the input and outputs.

Read it again. The regulation is very clear that the 462 MHz frequencies are for base stations and the 467 MHz frequencies are for mobiles and control stations.

 

[RFI-EMI-GUY]

(snip)you could use a separate 467Mhz channel for your control functions. (snip)
.
...........................................CF

A bit off topic, but gives me a very good idea for repeater control in urban area and dealing with jammers. For those designing their own repeater controller, one might consider a priority scan feature whereby if the repeater has a certain amount of activity indicative of abuse, the repeater toggles to a second input channel briefly (like priority interrupt on a VRS) so that the control operator can QSY and send DTMF shut down commands. Thus would save on having to deal with a second control receiver and would confuse the average meat head.

 

[kruser]

Not pertaining to GMRS,

I've seen UHF repeaters setup with reversed input and outputs but they still maintained the 5 MHz separation.

One of our local broadcast TV stations here has a 450/455 MHz repeater setup in reverse.

Why, I don't know why they did that but they did it many years ago and still runs in reverse to this day.

I figure they did it to thwart casual listeners or possibly frequency interference being as most of our broadcast stations have UHF repeaters in very close proximity to one another and duplexer technology was not the best back when 450 MHz started becoming popular.

Most are located at the studio's but some were installed on the broadcast antennas and I could see that being a problem when they are several hundred feet up on the broadcast antenna tower.

I think it was the local CBS station that runs in reverse but I could be wrong on that as it's been years since I monitored them. It used to be fun when they used those frequencies for aligning the STL links on 950 MHz from the remote vans.

 

[ecps92]

I know of one repeater owner who did that.
Jammer would sit right at / near the repeater, but we could shut it off via an additional 467 with a DTMF and unique DPL - The ID-10-T never figured it out...and via the extra RX, we could still chat.

A bit off topic, but gives me a very good idea for repeater control in urban area and dealing with jammers. For those designing their own repeater controller, one might consider a priority scan feature whereby if the repeater has a certain amount of activity indicative of abuse, the repeater toggles to a second input channel briefly (like priority interrupt on a VRS) so that the control operator can QSY and send DTMF shut down commands. Thus would save on having to deal with a second control receiver and would confuse the average meat head.

 

[ecps92]

O.T.
The Media 450/455 never had a preference nor a 5 Mhz band plan.
There are many Areas with 450 Repeaters and others with 455 Repeaters and the inputs are not (Your lucky if they are) always 5 Mhz offset

Not pertaining to GMRS,

I've seen UHF repeaters setup with reversed input and outputs but they still maintained the 5 MHz separation.

One of our local broadcast TV stations here has a 450/455 MHz repeater setup in reverse.

Why, I don't know why they did that but they did it many years ago and still runs in reverse to this day.

I figure they did it to thwart casual listeners or possibly frequency interference being as most of our broadcast stations have UHF repeaters in very close proximity to one another and duplexer technology was not the best back when 450 MHz started becoming popular.

Most are located at the studio's but some were installed on the broadcast antennas and I could see that being a problem when they are several hundred feet up on the broadcast antenna tower.

I think it was the local CBS station that runs in reverse but I could be wrong on that as it's been years since I monitored them. It used to be fun when they used those frequencies for aligning the STL links on 950 MHz from the remote vans.