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Digital in GMRS - which mode is most appropriate?

digital nxdn p25 dpmr idas mototrbo dmr

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#21 WRAF213

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Posted 05 December 2019 - 11:48 AM

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 What you're saying in that last post isn't consistent with what you said in your first post (P25 is obsolete vs. P25 offers nothing analog+DTMF can).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.


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#22 gman1971

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Posted 05 December 2019 - 02:01 PM

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.


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#23 gman1971

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Posted 05 December 2019 - 02:29 PM

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.



#24 intermod

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Posted 05 December 2019 - 04:52 PM

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 


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#25 intermod

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Posted 05 December 2019 - 06:22 PM

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.    


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#26 intermod

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Posted 05 December 2019 - 06:30 PM

Is this FB6 designation true? can this be verified?

 

Thank you.

 

Radioguy7268  is correct.  FB2 would also be fine for a private system.  However, the idle chit-chat that is common on GMRS is not actually permitted on the business/industrial service.   But in reality, it would never be challenged anyway as nobody really cares (including the Commission).     


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#27 gman1971

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Posted 05 December 2019 - 06:43 PM

Intermod, now you're talking!!! Almost like a mini GSM GMRS tower. :D

 

And now for the "dreaming is for free part"  <deep breath> "....if I was made out of gold, man, I would be on TETRA faster than I can blink..." <end dream mode>

 

G.

 

 

 

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 



#28 gman1971

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Posted 05 December 2019 - 06:55 PM

Wow, considering how bad I hate RF INTERMODULATION, I really like you intermod!! haha....

 

 

Radioguy7268  is correct.  FB2 would also be fine for a private system.  However, the idle chit-chat that is common on GMRS is not actually permitted on the business/industrial service.   But in reality, it would never be challenged anyway as nobody really cares (including the Commission).     



#29 intermod

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Posted 05 December 2019 - 07:31 PM

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. 

 

 

Several comments to Rich's post:

 

 - My experience also indicates equipment certification is the #1 issue. The FCC wants to maintain separate control over the GMRS space and manufacturers, and I get that.

 

 - I would avoid requesting the use of Part 90 equipment.  The petition should instead suggest any new Part 95 certification issues that might be appropriate**

 

 - Don't restrict the emissions - include those for all the major technologies (FXE, FXD, F1E, F1D, F1W , F7W)
 
 - Address "listen-before-talk", particularly §95.1731 Emergency communications
 
 - Attempt to get some manufacturer buy-in (the larger the manufacturer, the better)
 
  - Have multiple supporting GMRS groups endorse/support the Petition
 
 
Operationally, this will allow full-power mobile, control station and repeater operation.   But do we drop back to better ensure success, such as:
 
 - Propose reduced-power repeater operations initially (i.e., 5 watts TPO for first year or two??)
 
 - Propose simplex/direct mode only operation initially?
 
 - Operation only on the 462 MHz GMRS interstitials initially
 
 - Restrict repeaters to certain GMRS channels initially (yea, can-O-worms...)
 
 
 
** Such as automatic analog/digital decoding for pre-transmission monitoring / listen-before-talk; mandatory analog IDers for repeaters, etc.  Encryption, shared use of channels (related to linking) is already addressed in the rules and need not be changed.  


#30 intermod

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Posted 05 December 2019 - 07:35 PM

Wow, considering how bad I hate RF INTERMODULATION, I really like you intermod!! haha....

 

Maybe this was my nickname when I first cobbled together two Jobcomm portables with duct tape to make a repeater without using those pesky and expensive filter thingy's back in the 80's....


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#31 gman1971

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Posted 06 December 2019 - 04:26 AM

LMAO.. hahaha... pesky and expensive... indeed...

 

I would also think allowing mixed mode with FM would be great too. I believe Motorola repeaters can do both.

 

Oh man, I am already thinking about opening the flood gates and replace all the GMRS BF-888s house intercom with DMR... that is just going to be sooo cool... basically like those crappy old wireless phones with a station and a few extra handset, but this time on steroids!!! Dreaming is always for free tho.... :) haha

 

G.



#32 WQEJ577

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Posted 06 December 2019 - 10:14 AM

Maybe this was my nickname when I first cobbled together two Jobcomm portables with duct tape to make a repeater without using those pesky and expensive filter thingy's back in the 80's....

 

We now have four-letter words for people like that.  :D


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Rich Dunajewski

Founder, myGMRS.com

 


#33 gman1971

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Posted 06 December 2019 - 10:45 AM

LMAO... hahaha....

 

We now have four-letter words for people like that.  :D



#34 quarterwave

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Posted 06 December 2019 - 11:00 AM

FB2 is Single User Repeater

FB4 is Multiple User, "Community Repeater", Each user group (Ex: Bob's heating and cooling) is licensed for the repeater pair and their mobiles/portables.

FB6 is Multiple User, Common Carrier, Only the system (Repeater) is licensed, users are licensed as part of the system when they become users. 

FB7 Same as FB6 but non-profit

FB8 is a trunking repeater (centralized)


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#35 WRAF213

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Posted 08 December 2019 - 01:26 AM

Here's some excerpts from the FCC's 2017 rule change discussion:

 

Because the Personal Radio Services users typically share all the channels authorized for the service, it is important that all users be able to hear and understand each other in order to share channels and pass emergency messages.

 

[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...

 

Services that function on shared channels in this fashion rely on operators following a “listen before talk” etiquette and are essentially self-policed in that someone that may be operating in an inappropriate manner is informed by others of the appropriate use of the channels. Voice obscuring features as implemented may prevent users from readily understanding each other’s conversations complicating the sharing etiquette, hindering self-policing and communicating with others in calls for help...

 

[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.

 

We also decline to adopt a proposal to narrowband and digitize CBRS channels because 10 kilohertz channels are already relatively spectrally efficient and the digital emissions would be incompatible with the existing equipment base.

 

With the use of interstitial channels already in place and an established base of 25 kHz equipment held by individuals, any orderly switch to 12.5 kHz channels would be difficult, costly in lost equipment investments, and would not result in a material increase in spectrum efficiency.

 

The only way I see digital voice happening on GMRS is by creating a new service that's like GMRS but not, and digitizing from the start; type-certified equipment from the 1960s is probably still in use today, and there's no reason to fix what ain't broke.

 

 

But since we're speaking purely in hypotheticals here:

On the day pigs fly and there's a NPRM for digital voice (which is probably going to be a easily licensed 6.25 kHz modulation not common in commercial equipment (dPMR)), we suggest this as a rule: 462.675 MHz with a 141.3 Hz subaudible tone is officially recommended as a traveler's information channel, and no digital is allowed in the 25 kHz band centered at 462.675 MHz?

 

In reality, I would expect more digital voice exclusions, since analog repeaters would receive interference from any of four ultra-narrowband channels. It will actually have the effect of further overcrowding already overcrowded channels, since the new equipment will be purely interference to all existing equipment and only unidirectionally interoperable in the best case. To properly monitor the analog side, the ultra-narrowband receivers would need to either switch rapidly between the narrowband channel center on a 12.5 kHz step, and the ultra-narrowband channel center on a 6.25 kHz step, requiring a complicated and fairly expensive receive structure that would introduce additional confusion for the licensed-by-rule family members covered under the licensee's callsign. GMRS is already complicated enough, given the FRS/GMRS combination radio debacle. There's a whole list of reasons why DV, regardless of bandwidth, will never happen.


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#36 gman1971

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Posted 08 December 2019 - 03:51 AM

Fighting against change is the surest way to failure.

 

One thing is to state that digital is currently not legal, and leave it at that. I understand that, its the law, and we have to respect the law. But the "resist change to the last breath" attitude, especially when defending a technology that is pretty much obsolete in terms of features and quality of transmissions, I simply don't understand your radical posture against change for the better on GMRS.

 

Also, the excuses and lame reasoning you've given, aside from the legality matters, which can be addressed (laws can be changed), I see no reason why digital couldn't be allowed, and offer a lot of functionality that FM analog can't offer. 

 

You sound like the guys who fought fuel injection b/c carburetors were simpler to tune... 

 

And if you have interference from digital systems, then perhaps you need to use more filtering and better radios... since I am using TX/RX cavities the intermod/interference problems I had are all gone.

 

Even if only GMRS was remain fully analog, the rest of the spectrum is ALL going digital, there will be interference no matter how hard you try to prevent the inevitable.

 

G.



#37 berkinet

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Posted 08 December 2019 - 04:26 AM

Here's some excerpts from the FCC's 2017 rule change discussion:...
...The only way I see digital voice happening on GMRS ...

Fighting against change is the surest way to failure.

One thing is to state that digital is currently not legal, and leave it at that. I understand that, its the law, and we have to respect the law. But the "resist change to the last breath" attitude, especially when defending a technology that is pretty much obsolete in terms of features and quality of transmissions, I simply don't understand your radical posture against change for the better on GMRS.

Also, the excuses and lame reasoning you've given, aside from the legality matters, which can be addressed (laws can be changed), I see no reason why digital couldn't be allowed, and offer a lot of functionality that FM analog can't offer.

You sound like the guys who fought fuel injection b/c carburetors were simpler to tune....

I think you may be unfairly characterizing the previous comment. I believe @WRAF213 was quoting the FCC’s own comments as a way of shining light on what might and might not be views and proposals the FCC would be open to entertaining. He did not claim to support or reject those views.

My own personal view is that this discussion has pretty much served its purpose and it is now time to let it go before we reach the point of Godwin’s law: https://en.m.wikiped...ki/Godwin's_law
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Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth.

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#38 gman1971

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Posted 09 December 2019 - 12:34 AM

If that is the case, I am sorry.

 

In regards to the Godwin's law, nah, I am cool.  I just like my radios too much sometimes... :D

 

G.

 

I think you may be unfairly characterizing the previous comment. I believe @WRAF213 was quoting the FCC’s own comments as a way of shining light on what might and might not be views and proposals the FCC would be open to entertaining. He did not claim to support or reject those views.

My own personal view is that this discussion has pretty much served its purpose and it is now time to let it go before we reach the point of Godwin’s law: https://en.m.wikiped...ki/Godwin's_law


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#39 intermod

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Posted 14 December 2019 - 12:01 AM

But since we're speaking purely in hypotheticals here:

On the day pigs fly and there's a NPRM for digital voice (which is probably going to be a easily licensed 6.25 kHz modulation not common in commercial equipment (dPMR)), we suggest this as a rule: 462.675 MHz with a 141.3 Hz subaudible tone is officially recommended as a traveler's information channel, and no digital is allowed in the 25 kHz band centered at 462.675 MHz?

 

 

That is an interesting idea.  You must have seen how public safety maintained backwards-compatibility on their mutual-aid channels (interoperability) when Part 90 users were slowly transitioning to narrowband.   They kept them wideband, and did not allow any narrowband operations the 12.5 kHz adjacent channels, until the mutual-aids when narrow.

 

While we are not really going narrow, it would better protect and lock in an analog wideband channel for compatible emergency comms when needed.    



#40 intermod

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Posted 14 December 2019 - 01:04 AM

 

In reality, I would expect more digital voice exclusions, since analog repeaters would receive interference from any of four ultra-narrowband channels. It will actually have the effect of further overcrowding already overcrowded channels, since the new equipment will be purely interference to all existing equipment and only unidirectionally interoperable in the best case. To properly monitor the analog side, the ultra-narrowband receivers would need to either switch rapidly between the narrowband channel center on a 12.5 kHz step, and the ultra-narrowband channel center on a 6.25 kHz step, requiring a complicated and fairly expensive receive structure that would introduce additional confusion for the licensed-by-rule family members covered under the licensee's callsign. GMRS is already complicated enough, given the FRS/GMRS combination radio debacle. There's a whole list of reasons why DV, regardless of bandwidth, will never happen.

 

dPMR-like 6.25 might have been the approach if no other common digital mode existed.  But we have many now.  

 

You may have missed the earlier discussions here - interference has to do with signal level & proximity, not technology to any significant degree.  And the assumption that the number of users and interference sources would grow and cause overcrowding has no basis.  

 

In the end, changes in radio services and rules are always much simpler than you portray.  If the Commission simply permitted the typical digital emissions and made no change to analog operations or anything else - new digital radios would operate on existing channel centers.  Bandwidth is a don't-care.   And like today, if an analog direct-mode operation was interfered with, the victim would simply change channels until it went away.  Despite what the Commission believes, I have never seen one user call another and coordinate channel usage (FCC pipe-dream).  They can't - they are all in tone squelch, and if they could hear, they would just start spewing expletives at each other. 

 

Repeater operations would be the same as they are today - a new repeater owner would usually listen, select a channel, and work with the other co-channel repeater owners to arrive on a good (or least bad) channel.   In the beginning, most digital repeaters would be replacing existing analog repeaters - so the interference environment would remain unchanged.  Having the option to operate a digital repeater would not necessarily increase the total number of GMRS repeaters.  Digital repeaters are expensive enough that I cannot see many going up initially anyway.  User equipment is also slightly more expensive. 

 

What if a new digital repeater owner does not coordinate?  You listen for his (analog) Morse Code IDer, or buy the $90 digital radio with Promiscuous Mode and talk to them directly if you want to save time. 

 

Also - all the new digital equipment have an extremely good "busy-channel-lockout" features if it came down to it.   But like analog, nobody would want to use it. They would simply move their repeater to a different channel and avoid the headache (and likely jamming/self-policing). 

 

Would digital complicate the GMRS? Only for those who wanted to use digital.   If I don't want to understand it, then I could save money and just buy analog.      

 

Really - its just that simple. 







Also tagged with one or more of these keywords: digital, nxdn, p25, dpmr, idas, mototrbo, dmr

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