Digital in GMRS - which mode is most appropriate?

[intermod]

It is unclear if the FCC would consider permitting any digital voice modes in the GMRS in the near future, particularly since they just released new rules in 2017.  If they did consider this, should they permit a particular mode, such as P25, dPMR, DMR, NXDN, (other?), some, or all? 

 

Should it be limited to simplex/direct mode, or should repeaters be included?

[gman1971]

All good questions, all of which I don't know the answers.

 

But as a thought, (please don't burn me for the heresy hahahaha) why not make ALL channels narrowband 12.5, and split all the GMRS into 2 channels each? Should give more channels, potentially allow some sort of trunking?, and as a standard make the upper part of each wideband digital ONLY and the lower part of the old wideband channel ANALOG only. Again, just as a thought. Instead of 22 channels (excluding FRS and including GMRS repeater input) we would have 44 GMRS channels to chose from, so we could run more stuff and double the amount of pairs for repeater usage. But I am aware that it will be a massive change in regulations... so perhaps is not possible to implement.

 

 

G.

[WRAF213]

None, since vocoder licensing isn't fair for the consumer and causes more interference for analog users.

[gman1971]

Can you please elaborate this licensing thing?

 

None, since vocoder licensing isn't fair for the consumer and causes more interference for analog users.

[BoxCar]

Digital modulation and analog (F3E) are incompatible as digital modulation is a string of ones and zeros which sounds like a chain saw. In the Part 90 world where there are assigned frequency coordinators they have to maintain separation between digital and analog users on the same frequency to eliminate interference complaints. As GMRS doesn't have frequency coordinators insuring spacing between channels, allowing all types of modulation would be chaos.

[rdunajewski]

I don't think favoritism toward a particular standard would be in the best interest of the public, and likely wouldn't be specified by the FCC. What they are likely to do is specify a very limited set of emission designators which may or may not include the type of digital you're hoping to use (i.e. a TDMA format like DMR). So, if anyone has hopes of using DMR one day, they really need to make sure the FCC permits the associated emission type.

 

For example, here are some common formats and their emission designators. The last 3 digits are significant as they designate the modulation and type:

 

2-slot DMR (MotoTRBO) voice 7K60FXE

2-slot DMR (MotoTRBO) data 7K60FXD

 

P25 Phase I voice 8K10F1E

P25 Phase I voice 8K10F1D

 

P25 Phase II has several designators, of which 8K10F1W is one type

 

NXDN 6.25kHz (IDAS/NEXEDGE) voice 4K00F1E

NXDN 6.25kHz (IDAS/NEXEDGE) data 4K00F1D

NXDN 6.25kHz (IDAS/NEXEDGE) voice+data 4K00F1W

 

NXDN 12.5kHz (IDAS/NEXEDGE) voice 8K30F1E

NXDN 12.5kHz (IDAS/NEXEDGE) voice 8K30F1D

NXDN 12.5kHz (IDAS/NEXEDGE) voice+data 8K30F7W

 

We are most likely to see the voice emissions allowed but not sure about the data or combined voice+data modes. Note that DMR is actually FXE and not F1E, which means an oversight (intentional or otherwise) by the FCC could exclude DMR simply my omitting its emission type.

 

Now back to my opinion, I prefer DMR. Early on NXDN was a winner in my eyes, but once DMR became more openly supported and the Ham community embraced it, it has become the clear winner. Since we cannot benefit from 6.25 kHz channels on GMRS anytime soon, narrowband NXDN doesn't do anything for us except minimize adjacent channel interference, which typically isn't a big problem on GMRS to begin with. We just don't want to be locked into a particular standard and then when something new and improved comes out, we're locked in by the Part 95 rules. If it meets the emission designators, it would be open to use.

 

TDMA systems like DMR, however, allow us to use a 12.5 kHz channel (really a 25 kHz channel, but we're occupying 12.5 kHz in this case) with 2 time slots, or virtual channels. This doubles our efficiency on a given channel, even if GMRS isn't so busy to really need it right now.

 

It would be good for putting up one repeater and having 2 distinct usages like a private slot for the individual/family putting up the system, and a slot open for the public to use. The two groups can coexist and transmit simultaneously without affecting each other.

[rdunajewski]

Digital modulation and analog (F3E) are incompatible as digital modulation is a string of ones and zeros which sounds like a chain saw. In the Part 90 world where there are assigned frequency coordinators they have to maintain separation between digital and analog users on the same frequency to eliminate interference complaints. As GMRS doesn't have frequency coordinators insuring spacing between channels, allowing all types of modulation would be chaos.

 

I disagree, on FM this isn't an issue. If the 2 stations are far enough away that they do not interfere on analog, they would similarly not interfere on digital. It's only a problem when the two systems are close enough that analog interference would occur, then the digital signal would cause nearly identical interference. The problem is when a digital transmitter is transmitting all the time (like with trunking control channels), because the analog users would hear constant noise on the same channel (no matter how faint), rather than intermittent transmissions on a normal voice channel.

 

Remember, a digital radio transmission is NOT a digital waveform, and therefore is no more harsh on FM than an analog transmission. The wave is still a sine wave, but the modulation being applied to it results in one of a few levels of frequency shift, since it's FM (commonly 4-level FSK is used). That means that the carrier (present whether on analog or digital) is going to shift either up one of 2 frequencies or down one of two frequencies to represent 2 bits of data (00, 01, 11, 10) rather than only one (0 or 1). What you're hearing on an analog receiver is actually the rhythmic fluctuations of the modulation, shifting up and down as the bits are transmitted. 

 

By contrast, analog is rather chaotically modulated by the actual audio being transmitted (a much messier wave, but conveniently one that you can understand as a sound wave/speech/tone/etc).

 

At the end of the day, it doesn't matter what is modulating the carrier wave on FM. A digital signal doesn't actually go any further than an analog signal, it's just that a digital receiver can more easily distinguish, for example, one of 4 frequency shifts on a faint carrier than it could with 8 kHz of audio (including a CTCSS tone) to open up squelch. Hence, most digital radios have better sensitivity on digital (at the expense of a higher error rate in decoding the bits [known as BER - Bit Error Rate]).

[intermod]

There is a lot to unpack here....

 

But if I get what you are saying - create "new" channels so that existing systems have their own (original) channel, and new digital systems can operate on the other half - so they don't impact analog.  GMRS may not need more channels, but this permits both analog and digital.   

 

Narrowband and splitting is kind of what the FCC proposed in 2010 and decided against when they finalized it in 2017.   There was lots of opposition to narrowbanding; I think is was because of equipment replacement costs, among other issues.   

 

IMHO, trunking is just way too complex and requires regional cooperation and coordination, not to mentioned complete equipment replacement.  I am not sure what problem it solves.   I believe most GMRS repeater groups what to be independent with loose ties to other groups.   Trunking requires central management.     

 

You can operate conventional digital without having to trunk it.  And even the basic digital is bit more complex than analog to setup.      

     

All good questions, all of which I don't know the answers.

 

But as a thought, (please don't burn me for the heresy hahahaha) why not make ALL channels narrowband 12.5, and split all the GMRS into 2 channels each? Should give more channels, potentially allow some sort of trunking?, and as a standard make the upper part of each wideband digital ONLY and the lower part of the old wideband channel ANALOG only. Again, just as a thought. Instead of 22 channels (excluding FRS and including GMRS repeater input) we would have 44 GMRS channels to chose from, so we could run more stuff and double the amount of pairs for repeater usage. But I am aware that it will be a massive change in regulations... so perhaps is not possible to implement.

 

 

G.

[Durake]

IMHO, trunking is just way too complex and requires regional cooperation and coordination, not to mentioned complete equipment replacement.  I am not sure what problem it solves.   I believe most GMRS repeater groups what to be independent with loose ties to other groups.   Trunking requires central management.        

 

Agreed. Plus, if someone could afford a trunking system and have it dedicated to GMRS.......I would say that money would be better put elsewhere. Unless of course free radios capable of trunking are coming with it for all users who want to use it.

[intermod]

Digital modulation and analog (F3E) are incompatible as digital modulation is a string of ones and zeros which sounds like a chain saw. In the Part 90 world where there are assigned frequency coordinators they have to maintain separation between digital and analog users on the same frequency to eliminate interference complaints. As GMRS doesn't have frequency coordinators insuring spacing between channels, allowing all types of modulation would be chaos.

 

The topic was not whether digital has merit or not.   

 

But I disagree here.  As Rich indicated (correctly), interference has two key components, with one most dominant.  First, its a carrier-to-interference issue.  If two analog systems are too close, they interfere.  If they are far enough apart, they don't.  Digital is identical.  The duty-cycle (or duration that the transmitter is active) of an interfering system is the other component.  If the system is distant, it won't matter.  If its close, and on the air constantly, it will matter.   Part 90 frequency coordinators keep systems away from each other - does not matter which kinds.   

 

You might not like the sound in analog receiver, but that in itself is not interference.  Just run CTCSS/DCS. 

 

Digital in Part 90 was sometimes a concern when the duty-cycle of the interfering transmitter was too high.  This was often due to automatic vehicle location/GPS polling, or the owner enabled a beacon for network roaming or to simply chase competitors off the channel.  All of this can be addressed by the rules.

[intermod]

I don't think favoritism toward a particular standard would be in the best interest of the public, and likely wouldn't be specified by the FCC. What they are likely to do is specify a very limited set of emission designators which may or may not include the type of digital you're hoping to use (i.e. a TDMA format like DMR). 

 

....

 

Now back to my opinion, I prefer DMR. Early on NXDN was a winner in my eyes, but once DMR became more openly supported and the Ham community embraced it, it has become the clear winner. Since we cannot benefit from 6.25 kHz channels on GMRS anytime soon, narrowband NXDN doesn't do anything for us except minimize adjacent channel interference, which typically isn't a big problem on GMRS to begin with. We just don't want to be locked into a particular standard and then when something new and improved comes out, we're locked in by the Part 95 rules. If it meets the emission designators, it would be open to use.

 

TDMA systems like DMR, however, allow us to use a 12.5 kHz channel (really a 25 kHz channel, but we're occupying 12.5 kHz in this case) with 2 time slots, or virtual channels. This doubles our efficiency on a given channel, even if GMRS isn't so busy to really need it right now.

 

It would be good for putting up one repeater and having 2 distinct usages like a private slot for the individual/family putting up the system, and a slot open for the public to use. The two groups can coexist and transmit simultaneously without affecting each other.

 

This seems to be what they have done in the past.   Today they (a) allow a set of designators and ( b ) require the use of F3E.   While I don't like to see a technology "divergence" - many different modes being used - its only logical.   

 

I am also a DMR fan, exactly for the reason that it allows two simultaneous conversations on a 12.5 kHz narrowband channel.  Overall, GMRS does not necessarily need more channels in most areas - it needs a way for separate groups of users to share a common resource at the same time, without interfering with each other.  Having one repeater, duplexer and antenna support two separate channels (timeslots) at the same time, in half the bandwidth that analog GMRS takes, seems like good solution. 

 

Some of our users are not very sophisticated enough to understand CTCSS, DCS, the monitor button, etc., get frustrated with collisions and won't use the the radio now.  What happens when a group keeps colliding with another user on the same analog repeater?   They build another (wideband 25 kHz) repeater on a different channel.  So now we have a proliferation of repeaters.   

 

NXDN can operate at 12.5 or 6.25 kHz, but still only provides a single voice channel.  12.5 kHz does not buy you much, but 6.25 would likely allow use of the 467 interstitial/FRS direct mode/simplex channels at high power without interfering with repeater inputs.  In fact, you might be able to now run 6.25 kHz repeaters on the offset channels at power levels similar to the regular GMRS.   This might have some effect on the FRS users, however.          

 

P25 is one voice channel in 12.5 kHz.  Seems like limited value, as 12.5 Khz NXDN.  And expensive.  

 

DMR radios are now available at the $90-$100 level with tolerable quality.  

[intermod]

None, since vocoder licensing isn't fair for the consumer and causes more interference for analog users.

 

We are not saying the FCC should require digital - just give people the option to use it if they want.          

 

Digital does not cause more interference unless you can violate the laws of physics with it 

[rdunajewski]

I just don't see the ban going on for much longer. I think we as a community need to step up and make a convincing case, on the record with the FCC. When they denied the requests to permit digital voice, they specifically mentioned that there was insufficient discussion about it in the record, and thus they could not make a ruling. Once a Petition for Rulemaking is filed with a very narrow set of requests (not the kitchen sink arguments that were flying around last time -- mostly due to so so many proposed changes by the FCC, we had to defend all of them), key GMRS groups and radio manufacturers will have a chance to discuss it officially on the record and the FCC can make the determination.

 

Even still, the main issue I see with allowed digital voice is that no Part 95 equipment (to my knowledge) is even capable of being programmed to enable it. Maybe one or two models exist that carry dual Part 90 and 95 certification. Assuming the FCC even decided to lift the restriction on digital voice, one of three things will need to happen:

 

1. The manufacturers will need to begin adding digital to their lineup of radios. This is not impossible, as some low-cost dPMR radios exist for Europe, but I don't see it as something they want to jump at right now. I think the tide will turn within the next 5-10 years, but that's quite far off.
    
2. The FCC would need to permit GMRS licensees to use Part 90 equipment. We've been down this road before, and they pretty much completely shut down the argument. Their position seems to be that the manufacturers just need to submit their equipment for type certification and there would be no issue.
    
3. The manufacturers will need to begin certifying their equipment for Part 95 as well. For whatever reason, the manufacturers seldom cross-certify for Part 95. We're only just now getting some of the Chinese radios to have Part 95 certification (much to the chagrin of some of us), but getting Motorola, Kenwood, Icom, etc to follow suit has not been going very well. GMRS and FRS were lumped together so GMRS radios ended up being seen as bubble pack radios to sell at Walmart, not for more robust communications. Hopefully now that the combo radios are no longer able to be marketed, that means GMRS will finally get some non-bubble pack love.

Digital formats are finally working their way into cheaper radios (mostly DMR at this point), so hopefully the market for digital personal communications will continue to grow and the manufacturers will get serious about meeting the demand. I think this lack of motivation will be a driving factor in the FCC not permitting digital formats in the near future. I also think the bubble pack manufacturers will sit back and moan that digital doesn't do anything special and they don't want to hear complaints of interference. 

 

It will need to be a concerted effort to get this done, but I think the case can certainly be made. Everybody needs to be on the same page and the argument eventually has to be had on the record, not just online in forums. 

[gman1971]

In regards to the digital noise: I wouldn't blame the modulation type 'per se', but the radios that are doing the transmissions. The DMR CCR (Cheap China Radios) tidal wave is, based on my observations, the primary responsible for the digital noise mess, on both RECEIVE and TRANSMIT. First, those cheap transmitters make so much noise all over the spectrum that is just not even funny, so you have to keep the power really low, or it spews crap all over the place. Which is, unfortunately, not what a newcomer/beginner will do, they will crank power on their new CCR to 50W, b/c you know, running 50W is going to give them 50 miles of range, or more! haha.

 

After talking (and learning) from a member here, I now run bandpass cavities on all my high power Vertex Standard gear. And I have to say that the adjacent channels emissions, noise, etc, using whatever modulation FM, DMR, all have gone from barely detectable to undetectable at 10 yards on a 7.2 dBd gain antenna at 20 feet above a 2 story house, even when running it at 50W...  

 

Then, what I've also found out is that the CCR stuff is the most affected by noise too, regardless of it being DMR, NOAA, etc. The higher end Vertex gear, even without the cavities, was able to cope with the noise fairly well, but CCR radios like the GD77 or the TYT DMR mobile, etc, all those were pretty much desensed out of this world... so be aware that if you run a CCR, expect interference no matter what, and realize that is not THEIR radio what is causing the interference to you, its your own cheapie that simply can't handle the high RF environment.

 

Again, police and firefighters don't run CCR stuff for a reason, b/c receiver selectivity/dynamic range is pretty my critical to any radio these days, something the CCRs are not capable of coping with.

 

G.

[gman1971]

The NXDN 6.25 is, IMO, nothing but a gimmick. For the non-tech person it looks like a panacea. And at first glance, its pretty obvious that you want to do FDMA and not TDMA, but once you start calculating budgets and figuring out what you need, you quickly realize that double the equipment per frequency is in order, with even tighter filtering, so twice or triple the cost of a TDMA solution.

 

IMO, again, IMO, for a less complex  2-way radio system (vs a cellphone system), I think a TDMA solution makes a much better use of the spectrum (like GSM did). And, again, personally, if I could afford to run TETRA I really would, I really like the TETRA b/c it has 4 timeslots vs just 2 slot of DMR. A TETRA implementation on GMRS would actually make the use of repeaters great, b/c now 4 guys can be talking simultaneously without messing with each other's talks. You can now use a public repeater to selectively call IDs (groups, individuals), rather than keying the repeater (and all that are linked to it) at 3:25 AM in the morning and waking everyone up to hear "WXZX1245, hey honey, I am going home." And lets not forget that, effectively, with a DMR/TETRA GMRS solution in place, most folks would have little need to build their own repeater for a less public (not encrypted) channel. Making good repeaters (like the Madison 700) now a viable option to have a group call with just your family so it doesn't open the squelch for a guy sitting in Indiana, who probably isn't very interested in hearing when you're going home. Maybe he is, but if so, he can run a nice thing called "promiscuous mode" so you can hear all traffic in the linked repeater network, but then, that is HIS choice. For a public GMRS DMR I would also filter ANY and ALL encrypted calls. Don't run encrypted crap, please, thank you.

 

One possible way to do this on DMR would be: Assuming a hierarchy of Repeater -> Call Sign -> Family. Lets begin by assigning a repeater Group Call ID for every repeater, this Repeater Group Call ID will be issued to all the radios that connect to it via direct RF, so for example, for the Madison 700, the Group Call ID could be, say, ID 1000, and consequently all the registered radios that are in the Madison area will be listening to the 1000 Group Call. Then, when a new licensee signs up on the repeater, they get assigned two DMR IDs, first one is a Group Call ID, linked to your callsign, which will be then subsequently used by anyone under your callsign (ie. family) and a Private ID just for any new radio you get. So, now, when the wife gets a radio, all you get is another private DMR ID for that radio, and set the radio to listen to both the Group Call ID under your callsign and the Group Call for the repeater. So, now that GMRS repeater has become a pretty viable family comm service (which is what GMRS was meant to be) And then, b/c DMR allows to have 2 people talking at the same time (even more I think with the higher end Moto stuff)  so again, digital makes so much more sense IMO. So you can effectively utilize repeaters like the Madison 700 area to do what GMRS was really meant for, and without bugging everyone and their mother (and especially when the repeater is linked all the way to Indiana from Wisconsin... holy cow, my simple radio call "WQXXXX, hey honey, I am going home" was heard all the way down to Indiana... that doesn't sound very appealing to a lot of people, hence there will be much less "repeater proliferation")

That is just for basic GMRS family comms. But then you can create Group Calls for different things, like hobbies, say, there is a buch of GMRS guys who like RC planes and another who really likes "basket weaving", or guns, or Corvettes? No problem, create several group calls, ID 40001, 40002... so on so forth, and if you like RC planes, you just add that group ID to your personal radio, or if you like basket weaving you listen to that ID, so the guys who hate "basket weaving" don't have to listen to the "basket weavers" yap all day long about how awesome it is,etc. Same goes for RC planes, or whatever it is that floats your boat.

 

Again, this is just my opinion, I clearly understand that the current FCC regulations don't allow for any digital modulation at the time of this writing, so don't use digital, but then again, dreaming is for free.

 

G.

[WRAF213]

My biggest issue with digital on GMRS is the lack of interoperability. Different modes don't talk to different modes, and analog users (which would be all FRS users and all existing type-accepted GMRS equipment) will have no hope of ever being able to understand what is being said on a digital system. The only people who'd immediately benefit from a rule change are those who aren't using Part 95 equipment. Most importantly, 95.1731(a), ((1), and (c ) would no longer be effective if stations were no longer able to communicate due to differing modulations.

 

The FCC has already explained why they aren't going to do digital voice on GMRS, and they cite this reasoning:

 

We also note that seven parties filed petitions for rulemaking requesting that we allow a time division multiple access (TDMA) modulation technique (i.e., 7K60FXE 2‐slot DMR TDMA) on GMRS frequencies to facilitate digital emissions and narrowbanding to increase capacity on GMRS channels. We deny these petitions. As explained above, the ability of GMRS licensees to communicate with each other is essential for the “listen before talk” etiquette, self-policing, and emergency calls that occur on these shared channels, and introducing a new modulation technique that is inconsistent with existing equipment would complicate the shared environment of GMRS channels. Further, with the use of the interstitial channels by GMRS and FRS units, we do not feel that the gains achieved by implementing narrowband digital techniques outweigh the losses in equipment investments and complications of introducing a new modulation scheme for GMRS radios.

 

CTCSS/DCS is a flimsy excuse since operators using tone squelch can easily disable it to monitor for other traffic, and users with priority traffic can transmit with tone squelch. Even if they have to do it on a split-tone repeater's output frequency, there's still the chance that they'll be heard. Commercial digital radios are designed to mute traffic sent to other destinations (for example, private calls on DMR), so traffic addressing becomes a factor and impedes the capabilities of listen-before-talk. Promiscuous mode is not a standard feature.

 

Dual certification is more difficult after 6.25-equivalent narrowbanding requirements began to get implemented in Part 90, since the radio would be capable of transmitting a non-compliant emission designator or scrambled/encrypted traffic on GMRS channels. A set of significant changes to the programming software could resolve the issue, but that's additional costs and confusion for us and less planned obsolescence for the radio manufacturers. It's not impossible for a 6.25e radio to get dual certification since there's no requirement to prevent users from programming digital channels onto GMRS channels, but it's a big can of worms for the FCC and extra costs for the manufacturer.

 

If I had to pick a mode, and if licensing/equipment costs were assumed to be negligible, I would endorse P25 Phase 1. It's theoretically vendor-neutral, easy to modulate, better suited on simplex operation (NAC of F7E and non-talkgroup operation), and most of the equipment already out there already has mixed-mode capability. Unfortunately, we can't trust everyone to properly program their radios for mixed-mode operation and listen-before-talk.

 

GMRS isn't the place to set up commercial-type repeater systems, it's a place for travelers and family members to talk to each other. That's why we have the amateur bands.

[gman1971]

Well, my understanding is that GMRS was devised for family use, so why would anyone who is licensed want an unlicensed person, with an easy to acquire bubble pack radio, hear all their family traffic and cause interference, be it intentional or non-intentional. Now, I am fully aware that I can't prevent my radio signals from being listened by others (nor I have a need to prevent that), but say, if I switched tomorrow my entire GMRS setup to digital DMR, added RAS to a short range intercom repeater to limit who can talk through the repeater (not even going with AES encryption), etc, then all the neighbor kids who bought these 5W FRS radios after seeing the "cool" antennas going up on the roof of my house, these kids will no longer hear us talking on my house intercom, nor we'll hear them yap when we talk through the intercom and they also happen to be talking on their 5W portable as well.

 

Ham radio, amongst other reasons it was meant for tinkering and EMCOM, and you need a license to use it. The problem is, you see, that most 5 year olds can't get a ticket, most significant others (male and female alike) might not be interested enough to bother taking the exam, etc, so now, if you have a large family, say, 4 or 5 kids and wife, even if it was a family of little Mozarts who all were able to get their tech license by age of 4, the moment those 4-5 year old kids start swamping the ham channels with kid's talk about their latest GiJoe toy, or the Barbie that is pink, etc, the typical grumpo self-righteous ham operator will railroad the channel and assert grumpo dominance by stating "hey kids, you've hogged this frequency for your personal stuff, you need to move elsewhere.... this channel might be needed in an emergency situation." Even if all the 4 year olds were ham licensed. The moment anyone railroads on a private radio conversation for no reason, even if its a bunch of 4 years old, unless its an emergency, that anyone is the one causing harmful interference to those licensed operators, who where talking Barbies or pink unicorns on a ham frequency.

 

While the regulations are what they are now, it doesn't mean we can consider and discuss a future. Life is not set in stone, things evolve.

 

May I ask why P25 Phase I over analog FM? So they can run encryption? Which, BTW, its illegal to encrypt stuff in GMRS. P25 Phase I is the same thing as FM, it has nothing that can't be offered in FM analog with a DTMF setup.

 

Now, once you enter TDMA territory, the fact that you can have two conversations on a single frequency, and single frequency REAL TIME repeaters, which will make any radio a hotspot, etc, then P25 Phase I is, simply put, obsolete, b/c it doesn't offer anything that FM can't offer already, and then, like DMR, its not interoperable with FM either. So, IMO, if you are going to get digital, there has to be a reason, beyond having the little encryption checkbox, to make the swap. That reason, for me, the reason why I would go digital DMR is b/c I could implement single frequency repeaters (as in , receive in TimeSlot 1 and immediatly retransmit on TimeSlot 2, single frequency, no delays, NOT a simplex repeater) and then have two conversations going on at the same time on a single frequency, all that without having to buy any additional infrastructure. Can't touch that with FM nor P25 Phase I. 

 

G.

 

 

My biggest issue with digital on GMRS is the lack of interoperability. Different modes don't talk to different modes, and analog users (which would be all FRS users and all existing type-accepted GMRS equipment) will have no hope of ever being able to understand what is being said on a digital system. The only people who'd immediately benefit from a rule change are those who aren't using Part 95 equipment. Most importantly, 95.1731(a), ( (1), and (c ) would no longer be effective if stations were no longer able to communicate due to differing modulations.

 

The FCC has already explained why they aren't going to do digital voice on GMRS, and they cite this reasoning:

 

CTCSS/DCS is a flimsy excuse since operators using tone squelch can easily disable it to monitor for other traffic, and users with priority traffic can transmit with tone squelch. Even if they have to do it on a split-tone repeater's output frequency, there's still the chance that they'll be heard. Commercial digital radios are designed to mute traffic sent to other destinations (for example, private calls on DMR), so traffic addressing becomes a factor and impedes the capabilities of listen-before-talk. Promiscuous mode is not a standard feature.

 

Dual certification is more difficult after 6.25-equivalent narrowbanding requirements began to get implemented in Part 90, since the radio would be capable of transmitting a non-compliant emission designator or scrambled/encrypted traffic on GMRS channels. A set of significant changes to the programming software could resolve the issue, but that's additional costs and confusion for us and less planned obsolescence for the radio manufacturers. It's not impossible for a 6.25e radio to get dual certification since there's no requirement to prevent users from programming digital channels onto GMRS channels, but it's a big can of worms for the FCC and extra costs for the manufacturer.

 

If I had to pick a mode, and if licensing/equipment costs were assumed to be negligible, I would endorse P25 Phase 1. It's theoretically vendor-neutral, easy to modulate, better suited on simplex operation (NAC of F7E and non-talkgroup operation), and most of the equipment already out there already has mixed-mode capability. Unfortunately, we can't trust everyone to properly program their radios for mixed-mode operation and listen-before-talk.

 

GMRS isn't the place to set up commercial-type repeater systems, it's a place for travelers and family members to talk to each other. That's why we have the amateur bands.

[WRAF213]

Now, I am fully aware that I can't prevent my radio signals from being listened by others (nor I have a need to prevent that), but say, if I switched tomorrow my entire GMRS setup to digital DMR, added RAS to a short range intercom repeater to limit who can talk through the repeater (not even going with AES encryption), etc, then all the neighbor kids who bought these 5W FRS radios after seeing the "cool" antennas going up on the roof of my house, these kids will no longer hear us talking on my house intercom, nor we'll hear them yap when we talk through the intercom and they also happen to be talking on their 5W portable as well.

 

PRIVACY DOES NOT BELONG IN GMRS! That's EXACTLY why we're using analog! See 95.1733(c ):

(3) Coded messages or messages with hidden meanings (“10 codes” are permissible); 

Everyone is supposed to be able to hear everyone, and there is no expectation of privacy; in fact, there should be a reasonable expectation that others are able to hear you. RAS obfuscates transmissions even though it is not voice encryption. If you don't want to hear kids on pink Barbie radios or you don't want them to hear you, then you shouldn't be using post-2017 GMRS.

 

 

May I ask why P25 Phase I over analog FM? So they can run encryption? Which, BTW, its illegal to encrypt stuff in GMRS. P25 Phase I is the same thing as FM, it has nothing that can't be offered in FM analog with a DTMF setup.

 

What? P25 is not encryption, it's a digital voice format the same way DMR/NXDN is, and ham stuff like MMDVM is equally compatible. Digital voice operates better at FM threshold and/or with mobile flutter. P25, like other digital voice formats, also has embedded signaling, which analog FM can't offer.

 

DMR is 6.25 kHz-equivalent narrowband on repeaters only (yes, there's DCDM, but that's proprietary), and has worse voice quality than P25. The other timeslot gets wasted in direct mode with Tier I or II operation. dPMR and NXDN48 do not have that limitation due to their 6.25 kHz bandwidth, while P25 and NXDN96 put more data in a 12.5 kHz bandwidth.

[gman1971]

Holy pendantic bold caps reply man. Would you please read carefully what I said before jumping the gun? On my earlier post I stated very clearly that A) I don't care if people hear my stuff (as in, I have no expectation for privacy). B )  I also stated NOT use encryption, b/c, once again, its illegal. But thanks for reiterating what I've stated already in an all bold caps statement.

 

Oh, and I have a cellphone if I want privacy. (more like 10 of them, but whatever)

 

The GMRS regulations in effect are the ones post-2017, I use whatever regulations are currently in effect, b/c you know, that is what the FCC laws currently say. If you want to use old laws that have been superseded, that is your call, not mine.

 

Who said P25 was encryption?... not me, so, where did you get that from? I am fully aware that P25 is just another digital format based on the AMBE2 vocoder, etc.

 

Now, here is what I did said, and I will repeat it: P25 phase I is obsolete. And FM does offer DTMF signaling, sure, its not embedded, but you can achieve the SAME type of signaling for opening different radios, etc, on analog FM. I've done it in the past, is not as clean as DMR, but it can be done.

 

What? ham MMDVM is not equally compatible, dude, Multi Mode Digital Voice Modems are just devices that "translate" CAI to IP packets, not a ham digital format.

 

And why are we bringing here the fact it operates better at threshold? why is that relevant? It is pretty much a fact that FM wideband can reach further than anything digital at the moment. Sure, its arguably not going to be crystal clear, but you can copy stuff that the best digital radios simply won't decode... and then, there is always the cellphone.

 

As for P25 better quality than DMR, yeah, that is like your opinion, man, and everyone has one. That's not factual, b/c now here is my opinion, I think P25 sounds worse than Motorola XPR or Vertex EVX high end DMR radios. So, who is right? who cares.

 

Now, here are the facts, on DMR you CAN have:

-Single Frequency repeaters.

-Single Frequency, two concurrent conversations.

 

I think there is some confusion here: There is Tier I DMR which is basically no timeslots, no pulsing, and effectively a single 12.5 kHz digital carrier, the same as P25 Phase I. And then there is Tier II Dual Capacity Direct Mode, which allows for two concurrent calls on a simplex channel, and that is AFAIK, part of the DMR ETSI standard. Then there is Tier II Repeater Operation, which uses two timeslots on receive and two timeslots on transmit. So on any given repeater you can have 2 concurrent conversations using a repeater pair of frequencies, and I believe that with the advanced Moto repeaters you can do pseudo trunking using the timeslots so you can have more than just 2 voice channels.

 

When you say that one timeslot is wasted, Its not wasted, the other timeslot is just available for a 2nd conversation to take place. But hey, wait a minute... you can't have two conversations on the same channel on P25 Phase I.

 

G.

 

 

PRIVACY DOES NOT BELONG IN GMRS! That's EXACTLY why we're using analog! See 95.1733(c ):

(3) Coded messages or messages with hidden meanings (“10 codes” are permissible); 

Everyone is supposed to be able to hear everyone, and there is no expectation of privacy; in fact, there should be a reasonable expectation that others are able to hear you. RAS obfuscates transmissions even though it is not voice encryption. If you don't want to hear kids on pink Barbie radios or you don't want them to hear you, then you shouldn't be using post-2017 GMRS.

 

 

 

What? P25 is not encryption, it's a digital voice format the same way DMR/NXDN is, and ham stuff like MMDVM is equally compatible. Digital voice operates better at FM threshold and/or with mobile flutter. P25, like other digital voice formats, also has embedded signaling, which analog FM can't offer.

 

DMR is 6.25 kHz-equivalent narrowband on repeaters only (yes, there's DCDM, but that's proprietary), and has worse voice quality than P25. The other timeslot gets wasted in direct mode with Tier I or II operation. dPMR and NXDN48 do not have that limitation due to their 6.25 kHz bandwidth, while P25 and NXDN96 put more data in a 12.5 kHz bandwidth.

[Radioguy7268]

I'll just point out that if anyone wants to do UHF DMR, the FCC already allows for that. It's called Part 90 Private Carrier (FB6 designation). Go get a 10-year license - get a Coordinated Frequency pair, and have at it. You no longer need to be concerned about getting Part 95 certified equipment, you don't need to worry about who qualifies as a "Family" member, and you can go ahead and "rent" airtime to anyone you want to, at any price you choose to. There's no requirement to charge a set amount or fee to anyone as a Private Carrier - you get to set your own rates (Zero if you wish), and you get to decide who uses your system.

 

In 10 years' time, DMR will probably be the defacto standard for UHF/VHF conventional systems, but the FCC is slow to recognize trends when it comes to their standards of "interoperability". I think you'll spend a bunch of time herding cats & trying to get everyone to agree on the same type of Digital modulation scheme if you try to get the FCC to make a formal rule change for Part 95 GMRS.

[WRAF213]

And then there is Tier II Dual Capacity Direct Mode, which allows for two concurrent calls on a simplex channel, and that is AFAIK, part of the DMR ETSI standard. Then there is Tier II Repeater Operation, which uses two timeslots on receive and two timeslots on transmit. So on any given repeater you can have 2 concurrent conversations using a repeater pair of frequencies, and I believe that with the advanced Moto repeaters you can do pseudo trunking using the timeslots so you can have more than just 2 voice channels.

 

When you say that one timeslot is wasted, Its not wasted, the other timeslot is just available for a 2nd conversation to take place. But hey, wait a minute... you can't have two conversations on the same channel on P25 Phase I.

 

DCDM is part of the standard, but standardization isn't the problem. DCDM requires infrastructure, specifically a timing master, in order to keep units synchronized. Handhelds are capable of being the timing master, but their range is poor and the necessary beaconing will drain the batteries. DCDM does not work on mixed systems because there is no way to guarantee there's just one station claiming timing master. In effect, timeslots can't be established on the nationwide, uncoordinated channels that GMRS has. The signaling a repeater uses to establish timeslots is embedded between each timeslot. TDMA transmitters (either on the repeater's input or in simplex mode) don't transmit during that period, since that's a guard period between transmissions.

In TDMA direct mode, an elected channel timing leader MS shall establish the timing reference for both time slots on the frequency. MS units that are not the channel timing leader are responsible for retransmitting the timing reference out to the edge of the wide area system. This mechanism helps to ensure that all MS units in the wide area system are working from the same timing reference. In general a MS transmits in the appropriate slot with the channel slot timing established by the channel timing leader MS.

I was making specific reference to the post-2017 laws. What you're saying in that last post isn't consistent with what you said in your first post (P25 is obsolete vs. P25 offers nothing analog+DTMF can). P25 Phase 1 is still the ONLY P25 format for conventional operation, and it will be some time before we see any format include true direct-mode timeslotting. The hidden-node problem would prevent a radio from using whatever voice traffic it hears out there as a timing master. Solving that would require GPS timeslot edge references (not unattainable with current technology), which would increase equipment costs up to the public-safety realm. I don't think very many of us bought our radios new from a dealer, so we wouldn't be the market for it. Equipment cost is a real concern when the issue of FRS interoperability is introduced; it's still a band for toy radios for your kids.

 

P25 runs the vocoder at a higher rate than DMR, and equivalently has a higher data rate (7200bps vs. 3600bps after ECC). Yes, the vocoder is inferior, but it still fits in more voice information. Of course wideband FM is better, but that isn't what the topic is about. All digital voice modes will exceed narrowband FM at decode threshold, that's one of the biggest advantages of using digital voice and isn't an advantage of any one format. DMR uses less power for the same signal but only half of the channel's bandwidth can be realized.

 

This whole thread is just an example of why we'll be using analog for the next twenty years.

[gman1971]

Unfortunately for the old stuff, Vocoder tech does indeed make a huge difference.... enough difference to make DMR sound better at even (arguably) half the bitrate. So it is not about the theoretical max bitrate being transmitted, its about how much those bits are actually encoding useful information, and a better compression algorithm will provide, like MP3, better audio quality at lower bitrates. I like to compare Vocoders to the Fraunhoffer MPEG Layer-3 audio (MP3) which can store audio at 1/10 the bitrate of an uncompressed PCM 16-bit WAV file and deliver near identical quality to that. Sure, an MP3 is still not as good as a 16-bit PCM uncompressed, which in theory is not as good as a true analog LP vinyl 33 RPM, but it takes 1/10th (at 128 kbps rate) the space of a PCM to send nearly identical information to the analog LP signal, and because the brain knows how to put it back together (ECC is in your brain, filling all the missing FFT analysis gaps, etc) you get a pretty much near perfect song. The MP3 codec was far superior to pretty much all of the pre-MP3 era audio codecs that preceded it. and the bitrates needed for an Mp3 to sound great were almost unheard of at the time (1:10 compression ratio in the early 90s was huge, when most consumer hard drives were still measured in megabytes) The same principle pretty much applies to newer Vocoders. Hence why I say, P25 Phase I its obsolete. Much like DMR will be made obsolete once a new Vocoder tech, or something new comes along and renders it obsolete (like Tier I DMR). GSM is obsolete not because of the more sophisticated radio modulations, but because the increased processing power than didn't exist at the sizes of today three decades ago to make such advanced modulations feasible. Newer modulations ranging from OFDM, WCDMA, LTE, QAM....  cell phones can do gigabits per second on just RF... compared to a 9600 baud FM radio the difference is measured in orders of magnitude, that is just ridiculous. So, to sum this long winded paragraph. Its about useful information density, not the bitrate, more bits doesn't mean a better useful information density. Newer Vocoders offer that, older vocoders don't.

 

As for Dual Capacity Diret Mode, or DCDM, it requires no infrastructure to work at all. Please understand DMR terminology (not just read it from Wikipedia) before emitting such statements, DCDM is a simplex Tier II DMR feature and pretty much any DMR Tier II compatible radio I've tried can do it. Even my 44 dollar CCR Baofeng BF-1801 DMR (a low grade GD77 clone) radios can do DCDM, and have two conversations on a simplex frequency. Can't do that with P25 Phase I, nor analog. Again, DCDM is simplex ONLY.

 

Then you can also go with a Tier I DMR on simplex if you want to run legacy stuff, operating the thing on full single carrier, which is obsolete too b/c you pretty much throw away all the benefits that a Tier II TDMA system has to offer.

 

In a Tier II DMR environment you're not limited to having to use a repeater, you can choose what kind of infrastructure use: you can go with a simplex double slot approach, simplex DCDM, or even simplex Tier I continuous single carrier. And then if you need it, you can chose the repeater double slot option too. You have infrastructure options, which you simply don't have on legacy obsolete stuff. Sure, for ham, P25 Phasie I is certainly fine, to talk about that SWR increase of the newest patch cable on the shack, that doesn't matter, but for a commercial customer, having these options, it makes the difference. (also for a family too) ETSI TS 102 361-x (DMR) was designed pretty much from the ground up to replace FM analog. 

 

Timing slots are for the radios talking at any given moment, there is no need to create an universal timing for the entire country. At any given site, its either the radios themselves (double slot simplex, or dcdm simplex) or a repeater infrastructure that takes care of the timing, and when interconnecting different sites, either using IP Site connect, or any kind of MMDVM, b/c these convert CAI to IP, those packets get sent over the wire to be rebroadcast somewhere else, so how its timed or modulated back to CAI at destination is up to whatever is being done there. Hence why MMDVM can do all this multi mode "ham stuff", you get the IP packet, retrieve the digital voice information and pack it up as P25, NXDN, Fusion... etc.

 

Also, timing on a DCDM simplex setup (b/c there is no DCDM on repeaters since repeaters operate on 2 timeslots), DMR Tier II radios on DCDM simplex will select a timing leader automatically, and I can see that they will chatter once in a while for a fraction of a second to figure out the timing between all of them, so when you press the PTT, all the radios are already synced up and communication happens.

 

In regard to DMR radio mixed mode, my Alinco DJ-MD5 does DCDM simplex with mixed mode analog+digital on the same channel, and will transmit back on whatever modulation the last received transmission was on just fine: It can listen and demodulate correctly DMR or analog depending on the signal that is being received. There is no "interoperability" with FM problem there, but at the same time I have all the DMR Tier II options that a legacy system like P25 Phase I simply lacks.

 

I still don't understand why range, or operating near threshold is relevant to this discussion? Nobody has argued that having better audio to threshold is bad. DMR has that too.... but FM wideband will still reach further. In addition, RF range can be extended using the right infrastructure, better radios, or both. 

 

As for hearing kids on GMRS: here is what happens. First off, I don't hear them breaking the squelch, ever, I never said that. when I hear them is when key my BF-888S running @ 1 watt power, which opens the squelch on all the radios used in the intercom, but if at the same time I am keying my intercom, a 5W portable starts talking, I can hear both radios on the channel. That is the issue I've experienced, which has nothing to do with signaling. Now, when testing DMR all we noticed was a slightly lower audio quality. 

 

 

G.

 

 

DCDM is part of the standard, but standardization isn't the problem. DCDM requires infrastructure, specifically a timing master, in order to keep units synchronized. Handhelds are capable of being the timing master, but their range is poor and the necessary beaconing will drain the batteries. DCDM does not work on mixed systems because there is no way to guarantee there's just one station claiming timing master. In effect, timeslots can't be established on the nationwide, uncoordinated channels that GMRS has. The signaling a repeater uses to establish timeslots is embedded between each timeslot. TDMA transmitters (either on the repeater's input or in simplex mode) don't transmit during that period, since that's a guard period between transmissions.

In TDMA direct mode, an elected channel timing leader MS shall establish the timing reference for both time slots on the frequency. MS units that are not the channel timing leader are responsible for retransmitting the timing reference out to the edge of the wide area system. This mechanism helps to ensure that all MS units in the wide area system are working from the same timing reference. In general a MS transmits in the appropriate slot with the channel slot timing established by the channel timing leader MS.

I was making specific reference to the post-2017 laws. What you're saying in that last post isn't consistent with what you said in your first post (P25 is obsolete vs. P25 offers nothing analog+DTMF can). P25 Phase 1 is still the ONLY P25 format for conventional operation, and it will be some time before we see any format include true direct-mode timeslotting. The hidden-node problem would prevent a radio from using whatever voice traffic it hears out there as a timing master. Solving that would require GPS timeslot edge references (not unattainable with current technology), which would increase equipment costs up to the public-safety realm. I don't think very many of us bought our radios new from a dealer, so we wouldn't be the market for it. Equipment cost is a real concern when the issue of FRS interoperability is introduced; it's still a band for toy radios for your kids.

 

P25 runs the vocoder at a higher rate than DMR, and equivalently has a higher data rate (7200bps vs. 3600bps after ECC). Yes, the vocoder is inferior, but it still fits in more voice information. Of course wideband FM is better, but that isn't what the topic is about. All digital voice modes will exceed narrowband FM at decode threshold, that's one of the biggest advantages of using digital voice and isn't an advantage of any one format. DMR uses less power for the same signal but only half of the channel's bandwidth can be realized.

 

This whole thread is just an example of why we'll be using analog for the next twenty years.

[gman1971]

Is this FB6 designation true? can this be verified?

 

Thank you.

 

 

I'll just point out that if anyone wants to do UHF DMR, the FCC already allows for that. It's called Part 90 Private Carrier (FB6 designation). Go get a 10-year license - get a Coordinated Frequency pair, and have at it. You no longer need to be concerned about getting Part 95 certified equipment, you don't need to worry about who qualifies as a "Family" member, and you can go ahead and "rent" airtime to anyone you want to, at any price you choose to. There's no requirement to charge a set amount or fee to anyone as a Private Carrier - you get to set your own rates (Zero if you wish), and you get to decide who uses your system.

 

In 10 years' time, DMR will probably be the defacto standard for UHF/VHF conventional systems, but the FCC is slow to recognize trends when it comes to their standards of "interoperability". I think you'll spend a bunch of time herding cats & trying to get everyone to agree on the same type of Digital modulation scheme if you try to get the FCC to make a formal rule change for Part 95 GMRS.

[intermod]

The NXDN 6.25 is, IMO, nothing but a gimmick. For the non-tech person it looks like a panacea. And at first glance, its pretty obvious that you want to do FDMA and not TDMA, but once you start calculating budgets and figuring out what you need, you quickly realize that double the equipment per frequency is in order, with even tighter filtering, so twice or triple the cost of a TDMA solution.

 

 

Agree on the costs.  But if you need spectrum in a metro area, 6.25 kHz channels that may be the only thing available.   So you just eat the antenna, backup power system and additional rack space and site lease costs.   Ouch. 

 

TETRA - I forgot to mention this!   As GMRS uses 25 kHz wideband channels, that could support TETRA (I think it requires 21k bandwidth, so you would have to convince the FCC to go beyond the 20K GMRS limit; its already been done in Part 90).  Four TDMA slots would be more flexible than DMR's two and would further reduce message collisions among different groups. The handheld equipment is also quite nice, but still expensive.   

 

Since we have 25 kHz channels, it may be lower cost (considering both the repeater and user equipment) to simply split a GMRS channel in half and place two DMR transmitters there.

 

Normal Channel Center: 462.650

New Lower Channel Center: 462.650 MHz - 0.00625 MHz = 462.64375 MHz

New Upper Channel Center: 462.650 + 0.00625 = 462.65625 MHz

 

I just confirmed that the Motorola SLR5700 DMR repeater can be programmed for these channel centers.  Not sure about the CCRs.  

 

This now provides four repeater timeslots or channels in the place of one wideband analog channel.   Hmmm.....  

 

Greg 

[intermod]

While the commercial approach provides many things (allows DMR, group licensing, encryption, etc.), many repeater groups or clubs would no longer have free or low-cost rent at the repeater site.  Most site owners will charge full rent for "commercial" repeaters.  

 

It would also impact community service teams like CERT or Fire/Disaster Council groups that rely on the availability of very low cost "bubblepack" radios.  Yea, one can now buy $100 Part 90 radios, but once the group's designated "radio guy" decides to retire or leaves, nobody knows how to program the radios, or even understands where to buy them.