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GMRS Repeater Types ?


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#1 Beekeeper47

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Posted 29 August 2018 - 06:41 PM

I just became interested in GMRS in a effort to support my neighbors, who are already dabbling with low cost GMRS HT's.  I currently own a Midland Mobile system which covers FRS/GMRS frequencies. We have a local repeater on channel 20 with 5 Mhz offset .  My Midland Mobile is able to use channel 20 and has the ability to provide the needed code to use this repeater.  However, nothing in the Midland manual speaks about providing an offset. So here are my questions;

 

A) Can I access this repeater w/o the offset ?  

B ) Does the Midland Mobile automatically generate the needed offset ?  (It's just not indicated in the manual?)

C) Assuming the repeater owner will permit me to use his/her repeater, can I use the repeater in a simplex mode ?

D) Is the intent of having an offset to prevent low cost GMRS owners from using a repeater even if they know the needed access code.  (Thereby limiting use to more expensive radio users ....i.e. Motorola radios, etc.)  Reducing traffic being the intent.

E) Can a GMRS repeater automatic function  in a delayed simplex mode when it determines that a offset operation is not possible.

 

I apologize for all the questions, my knowledge of GMRS systems is limited and I'm have a hard time finding published information.  Thanks in advance for the help.

 

Regards,

Rich (WRCB692 & KI7LFD)



#2 n4gix

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Posted 29 August 2018 - 07:12 PM

Rich, all GMRS repeaters have a +5 MHz offset.  For example, a repeater on 462.675 will require your radio to transmit on 467.675 as well as the required CTCSS (PL) tone to access it.

 

Repeaters are by definition "half-duplex" since they use separate transmit and receive frequencies. They are called half-duplex because your radio cannot transmit and receive at the same time.

 

A cellphone or landline phone are "full-duplex" since both ends can talk and listen simultaneously.

 

If you use only one frequency, then it is known as "simplex" since you have to take turns talking! :)

 

GMRS repeaters are no different that any of your local 2m or 70cm ham repeaters. In that respect it is considered bad manners to use the repeater's transmit frequency for simplex operations.


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#3 Elkhunter521

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Posted 30 August 2018 - 12:34 AM

Currently, only 3 midland mobile's are repeater capable. The XMT400, XMT275, and the XMT115. Midland makes or has made several mobiles that are not repeater capable.
Be vewy vewy quiet.
I'm listening to my wadio!

#4 Beekeeper47

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Posted 30 August 2018 - 12:08 PM

Does 5 Mhz offset prohibits use by the XMT115 and other common lower cost GMRS radios with repeaters ? 

 

Nothing in the XMT115 manual refers to this offset. Or how to change the offset.  It does speak of the access codes, but not an offset.

 

Is the offset "fixed" in the radio such as the XMT400, XMT275, and the XMT115 ?   Whereas the access codes and "fixed" offset is not a feature in the lower cost HT's ?

 

By way of example, here is data from a  repeater:

 

 

 

Network:

 [None]

Type:

 Open System

Updated:

 August 10, 2018

 

 

Travel Tone: 

 Yes

ORI:

 Yes

Apprx. Range:

 13 Miles

Output: 

462.675 MHz   141.3 Hz

Input:

467.675 MHz   141.3 Hz

 

"Repeaters are by definition "half-duplex" since they use separate transmit and receive frequencies. They are called half-duplex because your radio cannot transmit and receive at the same time."

 

Can I assume, that lower cost HTs are only capable simplex operation and are not " half duplex" capable ?  That they both transmit and receive on the same frequency ?

 

I apologize for beating a dead horse, I'm a bit confused by what the manual indicates or fails to explain and the overall operation of repeaters with GMRS radios.

 

Thanks again for your patience.

 

Regards,

Rich



#5 PRadio

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Posted 30 August 2018 - 02:04 PM

Does 5 Mhz offset prohibits use by the XMT115 and other common lower cost GMRS radios with repeaters ? 

 

Nothing in the XMT115 manual refers to this offset. Or how to change the offset.  It does speak of the access codes, but not an offset.

 

Is the offset "fixed" in the radio such as the XMT400, XMT275, and the XMT115 ?   Whereas the access codes and "fixed" offset is not a feature in the lower cost HT's ?

 

By way of example, here is data from a  repeater:

 

 

 

Look on page 12 of your manual, under "Menu Mode Functions." The repeater function is there. If you don't have the manual, it is here: https://midlandusa.c...nal-24Oct16.pdf



#6 Hans

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Posted 30 August 2018 - 08:15 PM


A) Can I access this repeater w/o the offset ?  

B ) Does the Midland Mobile automatically generate the needed offset ?  (It's just not indicated in the manual?)

C) Assuming the repeater owner will permit me to use his/her repeater, can I use the repeater in a simplex mode ?

D) Is the intent of having an offset to prevent low cost GMRS owners from using a repeater even if they know the needed access code.  (Thereby limiting use to more expensive radio users ....i.e. Motorola radios, etc.)  Reducing traffic being the intent.

E) Can a GMRS repeater automatic function  in a delayed simplex mode when it determines that a offset operation is not possible.

 

 

A) No. GMRS repeaters operate with set input and output frequencies offset by +5 MHz. For example, 462.600 has an input frequency of 467.600 and an output of 462.600. The user's radio transmits to the repeater on 467.600 and receives on 462.600. That means that any simplex GMRS radio can hear the output on 462.600 but will not be able to open the repeater because it is not transmitting on 467.600. One cannot properly access the repeater without the offset between transmit and receive frequencies.

B ) Yes. The models that are repeater capable will automatically use a +5 MHz offset when rP is selected.

C) No. One cannot properly use a GMRS repeater without the offset. The repeater will never receive the signal if it is not transmitted on the input frequency, 467.xxx.

D) No. The offset is to allow the repeater to function properly. As such, it needs a separate transmit and receive frequency with enough offset to be able to filter out the other. There are parrot repeaters (store and forward) that use one frequency. A user transmits to the repeater. The repeater stores the audio and then transmits it back on the same frequency. It can be a pain to use and I'm not sure it is permitted in GMRS but I have heard a few on the air. As to the code. That's a sub-audible tone (we can't hear it but the radios can) used for squelching. Instead of having to set the carrier squelch of the repeater above a changing noise floor, tones allow the repeater to only open when the proper tone is transmitted. Although it also functions as a simple gateway for repeaters, there aren't that many tones and they can be easily captured by scanning or even guessed at.

E) Not really. One could be designed to do that, I suppose. But, it would be a royal pain for users. It would get very confusing in a hurry for the users as to which was stored and forwarded (simplex) traffic and which was not. Anyone close enough to receive the originating signal would not know if they were hearing the sent traffic or the repeated traffic. For such a mode, one has to wait for the originator to finish and the repeater to spit it back out.The tried and true method of two frequencies and an offset works very well. I wouldn't expect most repeater owners to even go through the hassle to set a Frankenstein like that up and I'm not sure how many users would use it given the high potential for confusing and aggravating operation.

 

Regarding Midland Micromobiles and repeaters...We have noticed a significant problem for some of our local users running Midland Micromobiles. I am told that they apparently cannot set the repeater frequencies to tone transmit and carrier squelch. If it transmits a tone, it requires the same tone on receive to open the squelch. The GMRS repeaters we have around here, and in all other places I've used them, do not necessarily output a tone per se. They rely on the transmitted signal from the user to contain the tone. The repeater just passes the audio through. That gets to be a problem when repeaters have multiple tones to access them like many I've used. If someone is accessing the repeater with a tone different than the Midland, the Midland will never hear the traffic. Likewise, if  a Midland user is listening for an open repeater to use, they will never hear already existing traffic using another tone. The Midland user will end up unwittingly transmitting with the other user. The work-around local Midland users have been doing is listening to the repeater output on another radio with carrier squelch (no tone). That is the only way that they can avoid talking over someone with a different tone and hear responses from users transmitting a different tone. Midland may have fixed that already or not. These radios were recent purchases (within the year) so I suspect that Midland has not addressed the issue.



#7 drollhauser

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Posted 22 March 2019 - 08:34 AM

Hi Rich,

If you haven't already figured out how to set up your MicroMobile for repeater access, you have to enable the repeater channels in the menu. By default the radio runs channels 1-7 and 15-22 all as simplex.

Press and hold the MENU button for 3 seconds to enter the main menu, scroll through the menu until you find RP, using the channel selector knob select RP ON, next press SELLECT then SCN/MON to exit the menu. At this point if you turn the channel knob you'll see channels 1-7, 15-22, and RP15-RP22. RP15-RP22 are your repeater channels with the fixed +5 MHz offset.

Unfortunately as mentioned above, the MicroMobiles only allow full CTCSS operation for tones so when you select a tone to access the repeater that's also your receive tone.

 

Dave

WRBP557/KB3CJT


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#8 Ian

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Posted 22 March 2019 - 07:43 PM

E) Can a GMRS repeater automatic function  in a delayed simplex mode when it determines that a offset operation is not possible.

 

 
Actually, that's … a really interesting idea.  A repeater controller that accepts input on the output frequency… but only when a particular tone code is used does it activate parrot mode.
 
Very clever, but probably best prototyped with ham radio equipment and frequencies.  Bet you could trivially achieve it with a Raspberry Pi as the repeater controller… 
 
 
These radios were recent purchases (within the year) so I suspect that Midland has not addressed the issue.

 

 
My MicroMobile XMT275 doesn't do this.  Unless they made changes since the New Years' sale, it hasn't been fixed.


#9 berkinet

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Posted 23 March 2019 - 02:27 AM

Actually, that's … a really interesting idea. A repeater controller that accepts input on the output frequency… but only when a particular tone code is used does it activate parrot mode.

Very clever, but probably best prototyped with ham radio equipment and frequencies. Bet you could trivially achieve it with a Raspberry Pi as the repeater controller…

Leaving aside the questionable legality of "simplex repeaters" on GMRS, just think a moment about this idea... How can a repeater listen on its own output? Presumable there would need to be two receivers listening to both input and output frequencies and then deciding how to respond based on which receiver picked up the signal. So, how could you ever switch back and forth between the two modes? What if there was one user on "simplex" and another in "repeater" mode, they could never communicate. All of this because someone can't program their radio, or bought the wrong radio.

My suggestion is, get a HAM license if you want to experiment. That is exactly what the amateur radio service is for. In the meantime, GMRS was designed for a specific set of use cases, and it seems to do those pretty well. I am not in favor of creating a second "amateur" radio service out of GMRS.
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#10 Ian

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Posted 23 March 2019 - 07:28 AM

To the best of my understanding, simplex receivers are kosher on the 462 repeater outputs.  This requires parsing Federal Registers, though, so your milage should be expected to vary, and neither of us, I suspect, are lawyers.

 

And this bizarre mixed-mode repeater is best developed on amateur channels, and only cautiously introduced to GMRS once the kinks are worked out.



#11 berkinet

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Posted 23 March 2019 - 09:08 AM

...And this bizarre mixed-mode repeater is best developed on amateur channels, and only cautiously introduced to GMRS once the kinks are worked out.

Perhaps I was being too subtle. Let me be a little more direct. It seems to me you spend a lot of time asking others for support in your quest for solutions for problems that do not exist. As to the specific suggestion about a Dual-Mode repeater, exactly what problem are you trying to address?  

 

If you are just dreaming of what could be, then as I have tried to tell you at least twice previously, there is already an excellent service for that, amateur radio. Instead of floating ideas you want other's opinions on, take the time to get a study book and take the ham radio technician test. Honestly, it is easy. If you can't grasp the (fairly basic) technological side at first, just study the questions and memorize the answers - believe me, you would not be the first person do do that.  The test consists of 35 questions drawn from a pool of 426 questions... and all 426 of them are available online or in print.  With a ham ticket (and a little money)  in hand, you would be free to start experimenting with some of your ideas.


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#12 Ian

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Posted 23 March 2019 - 05:07 PM

 

As to the specific suggestion about a Dual-Mode repeater, exactly what problem are you trying to address?  

Today, Beekeeper's question E.

 

 

 

If you are just dreaming of what could be, then as I have tried to tell you at least twice previously, there is already an excellent service for that, amateur radio.

Per HamStudy, I've reached 66% proficiency.  In another week, I should be able to sit for my licensing exam.


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#13 Hans

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Posted 24 March 2019 - 05:44 AM

Today, Beekeeper's question E.

 

Per HamStudy, I've reached 66% proficiency.  In another week, I should be able to sit for my licensing exam.

 

Yeah, in all fairness, you were answering the OP's direct questions. :)

 

Good luck on the test. If you ever get into DMR, maybe we'll make contact on the North America talkgroup.


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#14 Ian

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Posted 27 March 2019 - 02:08 AM

Yeah, in all fairness, you were answering the OP's direct questions. :)

 

Good luck on the test. If you ever get into DMR, maybe we'll make contact on the North America talkgroup.

I've got a GD-77s.  At the moment, it's set up to scan the GMRS repeaters in the region, on the off chance - but it has happened - that conditions are ideal enough I can hear 'em.  Even outdoors with fifteen watts, I can't get into 'em, though.  :|






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