DMR on GMRS

[intermod]

The SFR (for the reason you stated) is one of various radio applications digital allows.  The lowest cost hi-power commercial SFR unit I posted elsewhere is $400 (plus $120 shipping):

 

https://www.belfone.com/bf-sfr600-single-frequency-repeater_p66.html 

 

This Hytera portable also has this built-in:

 

https://www.hytera.us/products/pd982i-1

 

I can only imagine how handy the portable would be for search and rescue, etc. - just duct-tape it to a tree on a high hill in SFR mode (with an extended battery) and you are done.      

 

Other division duplex (TDD) products would include low power, 10-100 mW "hotspot" devices for under $150 - these are already developed for DMR in amateur.   They could then be networked..with full-duplex repeaters if needed. 

 

Greg  

[Lscott]

 

What would intrigues me about DMR are some of the radios that will function in SFR, single frequency repeater, mode. Of course you have to find one that works.

 

Anyway the attraction is no requirement for using any kind of "cavity" filters which would be necessary on a more traditional in-band system. This means almost anybody could setup a repeater with far less technical expertise required and cost for a decent set of BPBR filters. So until the FCC changes the rules we won't have DMR on GMRS. I do expect that to happen sooner or later, likely much later.   

 

Yes, to a point.  BUT you loose the TDMA aspect of it. Meaning that you can only have a single talk path when operating like this and this mode will require everything to be brand specific.  Motorola will work with Motorola, Kenwood with Kenwood. 

Now mind you, I am a commercial radio tech.  But I don't see how not needing a duplexer is that big of a deal on a fixed repeater.  Due to the fact we are limited to 50 watts of power, the small mobile duplexers that are typically rated for 40 watts would do a fine job and they are inexpensive on the used market.  Yes, there is the tuning aspect, but that's not a big deal.

 

 

I don’t believe using a radio in SFR mode requires all radios to be from the same manufacturer. They simply would be required to adhere to the tier 1 and 2 DMR standard. Only the single radio functioning in the SFR mode would be communing with normal DMR radios.

 

With the current rules a conventional analog in-band repeater requires two distinct frequencies, one in the 462.xxx range and the other in the 467.xxx range. So you have two frequencies used to support only one voice channel.

 

Using a SFR one could operate two repeaters, one on a 462.xxx frequency and the other on a 467.xxx frequency. You now have doubled the number of repeaters without consuming additional spectrum.

 

On simplex a number of radios can use what is referred to a Dual Slot Direct Mode. Apparently there are radios that will sync to each other using only one time slot without the requirements of a repeater to supply the time slot sync. What this does allows two such radios to use a single simplex frequency using just one of the two time slots. Another two radios on the same frequency could use the other time slot thus doubling the number of effective voice channels, again without consuming addition spectrum.

https://blog.retevis.com/index.php/whats-dual-capacity-direct-mode-dcdm/

 

https://www.kenwood.com/usa/com/lmr/tk-d240v_d340u/

 

 

[wrnv921]

I would be Amazed if the FCC allowed a European DMR system on an American Radios Service over the American P25 with maybe the NXDN system which is gaining Traction in the US..

Not something they normally do..

Edited August 23, 2022 by wrnv921
addendum

[Lscott]

45 minutes ago, wrnv921 said:

I would be Amazed if the FCC allowed a European DMR system on an American Radios Service over the American P25 with maybe the NXDN system which is gaining Traction in the US..

Not something they normally do..

Sooner or later the FCC will have to acknowledge the use of various digital voice modes on GMRS. If they don't it means the population of non regulation compliant users will just grow with no formal order to the whole thing. It's better they set the rules before it becomes too chaotic.

What digital mode(s) would be allowed, and where, is another whole topic. There are some past threads on the topic. You may find those worth your time to read through.

[SteveShannon]

1 hour ago, Lscott said:

Sooner or later the FCC will have to acknowledge the use of various digital voice modes on GMRS. If they don't it means the population of non regulation compliant users will just grow with no formal order to the whole thing. It's better they set the rules before it becomes too chaotic.

What digital mode(s) would be allowed, and where, is another whole topic. There are some past threads on the topic. You may find those worth your time to read through.

How many people use non compliant digital modes on GMRS now? I live in a GMRS desert so I have no idea. 

[gortex2]

I have heard a ton of digital on GMRS. Get near any port on the coast and its non stop. As I go thru DC and Baltimore I hear it on and off in the cities. Alot is simplex but I know of locations with repeaters on the air. Sad part is people buy CCR DMR stuff and just program away not knowing anything about rules or caring. When they sell stuff on amazon to anyone who has a CC its going to happen. When I was at a radio shop in the past they put a IDAS/NXDN repeater on GMRS for a school "cause they have no money" for licensing. I wasn't there much longer. All we can do as GMRS users is try to follow the rules and encourage others to do the same. 

[JAF27]

As a person based in New York City, we get a lot of it. I mean A LOT. Sometimes, DMR users will entirely occupy repeater output channels for hours while we are completely unable to hear our repeaters, even when using RX tones. 

Cheap Chinese devices like baby monitors also sometimes use digital signals on GMRS frequencies illegally. 

Rarely do I see use of the legal, short digital messages being used.

[Lscott]

13 hours ago, JAF27 said:

As a person based in New York City, we get a lot of it. I mean A LOT. Sometimes, DMR users will entirely occupy repeater output channels for hours while we are completely unable to hear our repeaters, even when using RX tones. 

Cheap Chinese devices like baby monitors also sometimes use digital signals on GMRS frequencies illegally. 

Rarely do I see use of the legal, short digital messages being used.

This is why the FCC will have to address allowing digital voice on GMRS sooner or later. It's happening with, or without, their official blessing. I would rather see digital voice incorporated officially in the rules, which hopefully will eliminate the chaos that currently exists. It also has to be coupled with some meaningful enforcement actions, at least directed towards the more frequent and flagrant violators.

Right now the complaints stem from DMR operation on GMRS. However I'll bet that's not the only digital voice mode you'll find in use on the service. There are plenty of commercial radios very capable of FM and digital modes such as NXDN and P25. I have several of those and some are Part 95 certified. Just can't use the digital half of the radio. Then you have some of the modified Ham gear, MARS/CAP mod's, running D-Star and YSF. A real smorgasbord to sort out.

I started a thread a while back about possible Part 95E rule changes to allow digital voice on GMRS. Seems like people don't care since the thread just died from lack of interest. Also it got derailed early on over lecturing about FHSS, which wasn't the point of the thread anyway. Oh well.

[JAF27]

3 hours ago, Lscott said:

This is why the FCC will have to address allowing digital voice on GMRS sooner or later. It's happening with, or without, their official blessing. I would rather see digital voice incorporated officially in the rules, which hopefully will eliminate the chaos that currently exists. It also has to be coupled with some meaningful enforcement actions, at least directed towards the more frequent and flagrant violators.

Right now the complaints stem from DMR operation on GMRS. However I'll bet that's not the only digital voice mode you'll find in use on the service. There are plenty of commercial radios very capable of FM and digital modes such as NXDN and P25. I have several of those and some are Part 95 certified. Just can't use the digital half of the radio. Then you have some of the modified Ham gear, MARS/CAP mod's, running D-Star and YSF. A real smorgasbord to sort out.

I started a thread a while back about possible Part 95E rule changes to allow digital voice on GMRS. Seems like people don't care since the thread just died from lack of interest. Also it got derailed early on over lecturing about FHSS, which wasn't the point of the thread anyway. Oh well.

You’re absolutely right. GMRS, as a modern radio service, has to address modern radio solutions like DMR.
 

The unfortunate fact is, adding DMR in such a large implementation would simply disrupt the millions of consumer analog radios that rely on the FRS/GMRS bands for communications. I’m tired of illegal DMR users flooding my repeater channels and making life a living hell.

 

I frankly believe that DMR should be applicable on only non-repeater channels, particularly channels 8-14 where power is limited to 0.5 watts. This way, users can experience its superior abilities while not disrupting other analog users.

[tweiss3]

25 minutes ago, JAF27 said:

I frankly believe that DMR should be applicable on only non-repeater channels, particularly channels 8-14 where power is limited to 0.5 watts. This way, users can experience its superior abilities while not disrupting other analog users.

Why? I'm half and half on DMR for GMRS, but when you sit down and think about it, DMR would allow for better co-use of a single repeater pair, with the added bonus of better coverage and other tools that quite frankly would be used in our house.

[JAF27]

16 minutes ago, tweiss3 said:

Why? I'm half and half on DMR for GMRS, but when you sit down and think about it, DMR would allow for better co-use of a single repeater pair, with the added bonus of better coverage and other tools that quite frankly would be used in our house.

I’m not against DMR use for repeaters - it’s a great resource and works tremendously well!

My issue is handling the limited bandwidth of GMRS for both analog and DMR users. HAM has so much space that analog and DMR repeaters can coexist peacefully. However, GMRS only has a few repeater channels, and for analog users, DMR would likely flood their repeaters with the annoying sound of that buzzing!
 

I have had numerous illegal DMR users transmit on the output channel of my repeater. Even squelching them out with PL tones doesn’t work, and the interference is incredibly frustrating.

[JeepCrawler98]

1 hour ago, JAF27 said:

I’m not against DMR use for repeaters - it’s a great resource and works tremendously well!

My issue is handling the limited bandwidth of GMRS for both analog and DMR users. HAM has so much space that analog and DMR repeaters can coexist peacefully. However, GMRS only has a few repeater channels, and for analog users, DMR would likely flood their repeaters with the annoying sound of that buzzing!
 

I have had numerous illegal DMR users transmit on the output channel of my repeater. Even squelching them out with PL tones doesn’t work, and the interference is incredibly frustrating.

This. GMRS is an analog service, with all legal hardware on the band putting out 12.5khz or 25khz FM modulation (technically SSB and AM would be allowed too, but nobody makes this). The problem with DMR is that it's disruptive to these kinds of radios - traditional analog PL's will often leak DMR through as they're triggered by the signal, and currently most DMR's radio transmit inhibit functions are set to listen to the presence of other digital signals only, in short even with the equivalent "BCL" enabled they'd walk all over analog traffic. DMR users have no way of knowing what non-DMR signals exist on frequency (not saying it's impossible to implement, it just doesn't exist).

Using DMR on the interstitial channels might be a workable solution, maybe even at full power, as they're 12.5khz wide and would fit reasonably well between the main GMRS channels when considering true signal bandwith, but asking it to co-exist with analog repeater systems on the same channels is trouble.

That's not to say that DMR is not more spectrum efficient, you have half the band width, and twice the time slots (which can also allow for single frequency full duplex repeaters), so it could effectively handle 4 times the traffic as a whole had it been what GMRS was based on, but that's not the case currently. The other stumbling block would be programming  - lots of folks have trouble with understanding repeater PL's, let alone talk groups, time slots, DMR id's, color codes, transmit inhibits, roaming settings, and what not - this would need to be made more intuitive to users first, perhaps even standardized by industry, as getting it wrong can seriously mess up the usability of a repeater.

Edited September 1, 2022 by JeepCrawler98

[Lscott]

1 hour ago, JAF27 said:

You’re absolutely right. GMRS, as a modern radio service, has to address modern radio solutions like DMR.
 

The unfortunate fact is, adding DMR in such a large implementation would simply disrupt the millions of consumer analog radios that rely on the FRS/GMRS bands for communications. I’m tired of illegal DMR users flooding my repeater channels and making life a living hell.

 

I frankly believe that DMR should be applicable on only non-repeater channels, particularly channels 8-14 where power is limited to 0.5 watts. This way, users can experience its superior abilities while not disrupting other analog users.

You might like this idea.

GMRS Digital Voice - 20220803.pdf

[WRAM370]

From my experience as a not-very-interested amateur radio license holder, I observed an interesting phenomenon occur on the local ham radio scene, as digital modes such as C4FM (Yaesu System Fusion) and DMR began to appear.

It absolutely killed the local ham radio scene.

People either embraced the technology, or hated it, and in that process, people got angry with those who disagreed with them (think modern day politics in America).

As such, there is little-to-no amateur radio activity on repeaters anymore, and amateur radio as we knew it, has got both feet firmly in the grave…in this neck of the woods. Dozens of repeaters go unused. 

Those who embraced the digital voice modes (or “the dark side” as many called it), started out on talkgroups with fairly large gatherings of hams. Over time, they would get the azz of one another, and break off into other talkgroups of smaller, more intimate groups (another way of saying, only those who can tolerate each other), because they realized they could just keep creating new talkgroups. Now there are hundreds, if not thousands, of talkgroups, where two or three hams talk, where they used to talk to large groups on their local analog repeater. Excellent use of bandwidth.

It is interesting to see the discussion of DMR, or perhaps some other form of modulation, on GMRS, with it’s limited bandwidth, and no requirement to understand anything at all about radios. When asked to share spectrum space with analog and digital users, I can only imagine what will happen.

My worthless and unsolicited opinion is…if you want to play with a DMR radio, get yourself over to amateur radio. All sorts of people struggling there with code plugs, color codes, time slots, etc. And these are people who have “passed” a test to demonstrate proficiency in radio operation.

I think there is too much effort being placed in trying to turn GMRS into amateur radio. People want internet linking, wide coverage repeaters, nets, vanity call signs, ARES/RACES affiliations, digital voice modes. It all exists over on ham radio.

 

 

[Lscott]

The rationale for pushing for digital voice modes has nothing to do with making GMRS an “Amateur Radio Lite” service. In fringe areas FM doesn’t result in clear reliable communications. Having the option to use digital voice, and the documented better received audio signal quality in conditions where FM signal quality is poor, is the point. 

[JAF27]

4 minutes ago, Lscott said:

The rationale for pushing for digital voice modes has nothing to do with making GMRS an “Amateur Radio Lite” service. In fringe areas FM doesn’t result in clear reliable communications. Having the option to use digital voice, and the documented better received audio signal quality in conditions where FM signal quality is poor, is the point. 

Certainly. He is just mentioning that many people want to make GMRS another version of HAM, part of that being the move towards DMR. And yes, it is true. Many view GMRS as the easier and study-free way to use radio, but HAM was created for the sole purpose of radio enthusiasm and interest. 

[gortex2]

9 hours ago, WRAM370 said:

I think there is too much effort being placed in trying to turn GMRS into amateur radio. People want internet linking, wide coverage repeaters, nets, vanity call signs, ARES/RACES affiliations, digital voice modes. It all exists over on ham radio.

I have been saying this for 2 years. Every day its worse and worse. GMRS had a purpose and folks want to change it. I dont see folks screaming to add repeaters and P25 to MURS. Get over it and use GMRS for what it is. 

[WROZ250]

10 hours ago, Lscott said:

The rationale for pushing for digital voice modes has nothing to do with making GMRS an “Amateur Radio Lite” service. In fringe areas FM doesn’t result in clear reliable communications. Having the option to use digital voice, and the documented better received audio signal quality in conditions where FM signal quality is poor, is the point. 

DMR is, at the fundamental level, still FM radio. 

Yes, the way the signal degrades with range is better than analog FM, but the overall range is about the same.  It is simply that the digital tends to maintain voice quality better than analog until the dropout point whereas analog quality degrades semi-linearly as the distance increases.  The perception of range, all things being equal, appears better with digital.

If there is any real valid reason to allow digital, in the case of DMR for example, it is the ability for a repeater to provide 2 radio channels (using two time slots) on a single frequency, of which two simultaneous, separate, conversations can take place at the same time.  Basically doubling the available 'channels'  This is true for subscriber units as well.

All that said, it is unlikely the FCC will consider digital for GMRS anytime soon.  One would think if that were the case, they would have done it with the last major revamp a couple of years back.   Will/Could it happen, sure.  But I wouldn't hold my breath.

Even if the FCC were to do it, it brings up another, perhaps bigger issue that other posters have pointed out.  There are many GMRS users now who struggle just to program their existing analog FM radios, others still who don't completely grasp the concept of basic repeater operation and things like CTCSS or DCS.

I can say with a bit of authority that programming a DMR radio isn't something the average GMRS user is capable of doing, at least not without assistance, as it is many times more complicated than configuring analog FM radios.  Compound that with proper usage of DMR.  Also, things like who ensures that digital IDs are not duplicated?

IMHO, adding digital to GMRS has many potential pitfalls, the least of which is the FCC granting permission to do it.
 

[Lscott]

20 minutes ago, WROZ250 said:

DMR is, at the fundamental level, still FM radio. 

Yes, the way the signal degrades with range is better than analog FM, but the overall range is about the same.  It is simply that the digital tends to maintain voice quality better than analog until the dropout point whereas analog quality degrades semi-linearly as the distance increases.  The perception of range, all things being equal, appears better with digital.

If there is any real valid reason to allow digital, in the case of DMR for example, it is the ability for a repeater to provide 2 radio channels (using two time slots) on a single frequency, of which two simultaneous, separate, conversations can take place at the same time.  Basically doubling the available 'channels'  This is true for subscriber units as well.

All that said, it is unlikely the FCC will consider digital for GMRS anytime soon.  One would think if that were the case, they would have done it with the last major revamp a couple of years back.   Will/Could it happen, sure.  But I wouldn't hold my breath.

Even if the FCC were to do it, it brings up another, perhaps bigger issue that other posters have pointed out.  There are many GMRS users now who struggle just to program their existing analog FM radios, others still who don't completely grasp the concept of basic repeater operation and things like CTCSS or DCS.

I can say with a bit of authority that programming a DMR radio isn't something the average GMRS user is capable of doing, at least not without assistance, as it is many times more complicated than configuring analog FM radios.  Compound that with proper usage of DMR.  Also, things like who ensures that digital IDs are not duplicated?

IMHO, adding digital to GMRS has many potential pitfalls, the least of which is the FCC granting permission to do it.
 

You have some valid points.

I think the issue with going digital has more to do with improved voice quality than anything else. There is some possible range improvements, likely due to digital voice modes to maintain clear communications until you reach the range limit. As you pointed out the signals propagate the same regardless of mode. I suspect the attraction of digital voice for the average non-technical GMRS user is clarity of the audio signal under conditions where analog FM will sound like crap. It's a better user experience.

The issue with how to configure the radio for digital mode(s) can be addressed by restricting the options. For example all compatible radios must use the same time slot, or likely both, the group ID can be fixed (All Call), leaving leaving just the color code as an option.

Remember the EU has the dPMR446 license free service. The use of DMR isn't really the only choice. I wish people would get that out of their head and consider the other modes that might be much better, simpler, from a user's view point. There are other digital voice modes requiring less setup, such as the one I just mentioned. I have the programming software for the Kenwood TK-3701D, which is an EU license free analog/PMR446 radio, just to see what it looks like. See attached file for an example of the digital half of the radio memory setup. It's really not that complex, on a par with analog FM.

Part of the issue with getting the FCC to consider digital voice mode(s) will be how to fit it into the existing GMRS service given it's current limitations. DMR might not be the best idea regardless of how "popular" it is. People are using it simply because it's readily available with somewhat affordable radios. As some others have pointed out it's already causing problems. Using a different digital voice mode with some sane rule changes that can be fixed IMHO.

[JAF27]

42 minutes ago, Lscott said:

You have some valid points.

I think the issue with going digital has more to do with improved voice quality than anything else. There is some possible range improvements, likely due to digital voice modes to maintain clear communications until you reach the range limit. As you pointed out the signals propagate the same regardless of mode. I suspect the attraction of digital voice for the average non-technical GMRS user is clarity of the audio signal under conditions where analog FM will sound like crap. It's a better user experience.

The issue with how to configure the radio for digital mode(s) can be addressed by restricting the options. For example all compatible radios must use the same time slot, or likely both, the group ID can be fixed (All Call), leaving leaving just the color code as an option.

Remember the EU has the dPMR446 license free service. The use of DMR isn't really the only choice. I wish people would get that out of their head and consider the other modes that might be much better, simpler, from a user's view point. There are other digital voice modes requiring less setup, such as the one I just mentioned. I have the programming software for the Kenwood TK-3701D, which is an EU license free analog/PMR446 radio, just to see what it looks like. See attached file for an example of the digital half of the radio memory setup. It's really not that complex, on a par with analog FM.

Part of the issue with getting the FCC to consider digital voice mode(s) will be how to fit it into the existing GMRS service given it's current limitations. DMR might not be the best idea regardless of how "popular" it is. People are using it simply because it's readily available with somewhat affordable radios. As some others have pointed out it's already causing problems. Using a different digital voice mode with some sane rule changes that can be fixed IMHO.

Solid points. I’d much rather DMR be integrated into MURS than GMRS considering it is a radio service that is nearly dead in many places, with only a few using it. Allocating 2-3 MURS channels for DMR wouldn’t do much harm.

It would be extremely hard to police DMR on GMRS. Analog users can’t interpret their signals, and if anyone went out of bounds just once, it could be a nightmare for analog users who would be unable to trace the signal’s origin. 

[Lscott]

1 minute ago, JAF27 said:

Solid points. I’d much rather DMR be integrated into MURS than GMRS considering it is a radio service that is nearly dead in many places, with only a few using it. Allocating 2-3 MURS channels for DMR wouldn’t do much harm.

It would be extremely hard to police DMR on GMRS. Analog users can’t interpret their signals, and if anyone went out of bounds just once, it could be a nightmare for analog users who would be unable to trace the signal’s origin. 

Yes, DMR might make sense for MURS. It's already sort of a catch-all garbage service as it is with people using remote doorbells, wireless data logging devices etc. I doubt DMR would do much more to mess it up than all the other crap that's there now.

[JAF27]

4 minutes ago, Lscott said:

Yes, DMR might make sense for MURS. It's already sort of a catch-all garbage service as it is with people using remote doorbells, wireless data logging devices etc. I doubt DMR would do much more to mess it up than all the other crap that's there now.

Where I am, one user uses the 154.6 frequency on FM for about one hour each morning (7 AM). I have scanned for miles in other areas, and that’s about it.

[Lscott]

1 hour ago, JAF27 said:

Where I am, one user uses the 154.6 frequency on FM for about one hour each morning (7 AM). I have scanned for miles in other areas, and that’s about it.

The FCC rules allows all matter of stuff that's prohibited on GMRS. I don't doubt that some areas may see little use, but that doesn't alter what is authorized.

https://www.ecfr.gov/current/title-47/chapter-I/subchapter-D/part-95/subpart-J/section-95.2731

What is notable is I don't see any limitation on the duration of those permitted uses. That would imply they can be used at high duty cycles.

[JeepCrawler98]

1 hour ago, Lscott said:

The FCC rules allows all matter of stuff that's prohibited on GMRS. I don't doubt that some areas may see little use, but that doesn't alter what is authorized.

https://www.ecfr.gov/current/title-47/chapter-I/subchapter-D/part-95/subpart-J/section-95.2731

What is notable is I don't see any limitation on the duration of those permitted uses. That would imply they can be used at high duty cycles.

The only gotcha there would be the interference clause:

Quote

§ 95.2725 MURS interference. MURS station operators must take reasonable precautions to avoid causing harmful interference. This includes monitoring the transmitting frequency for communications in progress before transmitting, and other measures as may be necessary to minimize the potential for causing interference.

DMR, NXDN, P25 also aren't authorized emission types, which we already knew, but it also mentions continuous carriers?:

Quote

 

§ 95.2771 MURS emission types.

A MURS transmitter must transmit only emission types A1D, A2B, A2D, A3E, F2B, F1D, F2D, F3E, and G3E. Emission types A3E, F3E and G3E may include selective calling or tone-operated squelch tones to establish or continue voice communications. MURS transmitters are prohibited from transmitting in the continuous carrier mode.

 

Can you get away with it? Probably, after all it's "just" MURS, as was already mentioned it's already a catch-all for all sorts of interference causing applications.

Edited September 2, 2022 by JeepCrawler98

[Lscott]

The continuous carrier bit is confusing. One could interpret that as 100 percent duty cycle or would that be CW type communications using Morse code? I'm guessing it's  the 100 percent duty cycle one.

The interference part seems to be ignored. I can't see how how a remote doorbell- pager will monitor for channel activity without the incorporation of a BCL, busy channel lockout, function. Same with telemetry systems etc. I think these applications just TX in the blind and screw any other traffic that happens to be there.

Anyway MURS, Multi Use Radio Service, is the garbage band for stuff nobody wants elsewhere on VHF.