DMR on GMRS

[KAF6045]

I'd have expected it to be a reference to CW/Morse -- in which the carrier is all that is transmitted, and it is cycled on-off. If CW were permitted, I'd expect to see it in the list of emission types. However, a portion of the rules that was NOT quoted above is:

Quote

§ 95.2757 MURS duration of transmissions.

MURS stations may not be operated in the continuous carrier transmit mode.

From which I'd interpret it to mean: can not use it as a broadcast station; one must pause to receive...

CW would be A1A, F1A (or G1A -- frequency modulation vs phase modulation tend to both be decoded the same way). So that too could be a prohibited mode as it is not listed.

 

[Lscott]

2 hours ago, KAF6045 said:

I'd have expected it to be a reference to CW/Morse -- in which the carrier is all that is transmitted, and it is cycled on-off. If CW were permitted, I'd expect to see it in the list of emission types. However, a portion of the rules that was NOT quoted above is:

From which I'd interpret it to mean: can not use it as a broadcast station; one must pause to receive...

CW would be A1A, F1A (or G1A -- frequency modulation vs phase modulation tend to both be decoded the same way). So that too could be a prohibited mode as it is not listed.

 

That makes more sense.

[WRKC935]

On 9/2/2022 at 6:58 PM, KAF6045 said:

I'd have expected it to be a reference to CW/Morse -- in which the carrier is all that is transmitted, and it is cycled on-off. If CW were permitted, I'd expect to see it in the list of emission types. However, a portion of the rules that was NOT quoted above is:

From which I'd interpret it to mean: can not use it as a broadcast station; one must pause to receive...

CW would be A1A, F1A (or G1A -- frequency modulation vs phase modulation tend to both be decoded the same way). So that too could be a prohibited mode as it is not listed.

 

Well, your right and wrong.  The emmision for CW is indeed A1A.  However, a repeater ID is NOT transmitted as CW.  It's Morse Code as a tone transmitted on an FM carrier.  The transmitter is legal due to this.  NO one with an FM repeater gets an emission designator on their license for CW (A1A) because of this.  Because they are NOT transmitting CW they are transmitting Morse Code.  The CW emission A1A, is a modulation technique where the carrier is switched on and off as the method of modulating the carrier.  If you were to hear a true CW emission on an FM radio it would be carrier being switched on and off.  Basically it would sound like someone kerchunking the repeater and sending CW doing so.  What you hear is an FM carrier that is modulated with a tone generator transmitting Morse Code intelligence on that carrier. 

[JAF27]

35 minutes ago, WRKC935 said:

Well, your right and wrong.  The emmision for CW is indeed A1A.  However, a repeater ID is NOT transmitted as CW.  It's Morse Code as a tone transmitted on an FM carrier.  The transmitter is legal due to this.  NO one with an FM repeater gets an emission designator on their license for CW (A1A) because of this.  Because they are NOT transmitting CW they are transmitting Morse Code.  The CW emission A1A, is a modulation technique where the carrier is switched on and off as the method of modulating the carrier.  If you were to hear a true CW emission on an FM radio it would be carrier being switched on and off.  Basically it would sound like someone kerchunking the repeater and sending CW doing so.  What you hear is an FM carrier that is modulated with a tone generator transmitting Morse Code intelligence on that carrier. 

Yes, good point. In simple terms, Morse Code on GMRS is never transmitted with an oscillator in the form of “Continuous/Carrier Wave” embedded into the signal, but rather in the form of audio being transmitted on FM.

[Adamdaj]

On 11/23/2017 at 10:12 PM, parighttobeararms said:

when are we going to be able to go to DMR on the GMRS Service i would love it to see us able to use DMR on the gmrs System 

The FCC has a better chance of increasing the power output on MURS, before they approve digital mods on GMRS. DMRS sounds like a good idea on GMRS. It would certanintly would allow users to make good use of repeaters as far as adding talk goups. Unfortunately, GMRS was intended for Short Distance as 11m CB radio was. Of course, the FCC had dropped the indivdual licensing requirment back mid 1980's for Class D Citizen Band Radio.  The Short Distance isn't observed, because when I think of Short Distance, I'm thinking of less than 5 square miles or less than that. With the use of a repeater or a network of repeaters on same pair, it goes beyond Short Distance.

[KAF6045]

4 hours ago, Adamdaj said:

Unfortunately, GMRS was intended for short distance as 11m CB radio.

Short distance, and primarily with users all under the same license (family farm, small business) -- licensee to licensee was extremely rare if not actively discouraged. It's really only after the FRS fiasco that the "General" in GMRS took primary aspect (rather than the "Mobile" -- it used to be that base-station to base-station was not permitted at all, and base-station to repeater was [and may still be depending upon how one interprets that "base-station" is listed under the 462MHz simplex category, but not under the 467MHz repeater category -- essentially, the base-station would have to BE the repeater with a microphone front-end attached... and again that means only 462MHz outputs [) also not permitted.

[gortex2]

I miss the "old" GMRS days. It was much simpler and no one was on my repeaters unless I wanted them on them. And when they were they had a real radio.

[Sshannon]

21 minutes ago, gortex2 said:

I miss the "old" GMRS days. It was much simpler and no one was on my repeaters unless I wanted them on them. And when they were they had a real radio.

Get off my lawn!

[zzz]

On 11/23/2017 at 9:12 PM, parighttobeararms said:

when are we going to be able to go to DMR on the GMRS Service i would love it to see us able to use DMR on the gmrs System 

What does "go to DMR" mean? 

[Sshannon]

7 minutes ago, zzz said:

What does "go to DMR" mean? 

Adopting digital voice mode “Digital Mobile Radio”, which is allowed on the amateur service and business radios. It would require a change to regulations and as far as I can tell there’s really no probability of it happening.

[zzz]

4 minutes ago, Sshannon said:

Adopting digital voice mode “Digital Mobile Radio”, which is allowed on the amateur service and business radios. It would require a change to regulations and as far as I can tell there’s really no probability of it happening.

Does that mean that currently any data transmitted using gmrs today, i.e text messages, are still analog?

[Lscott]

19 minutes ago, zzz said:

What does "go to DMR" mean? 

https://en.wikipedia.org/wiki/Digital_mobile_radio

[Lscott]

1 minute ago, zzz said:

Does that mean that currently any data transmitted using gmrs today, i.e text messages, are still analog?

That's sort of correct. So far the FCC has NOT authorize any type of "digital voice" modes. People are hearing digital voice signals, not necessarily only DMR, on GMRS breaking the rules. Some very brief "data only" transmissions are allowed with significant restrictions. 

I think sooner or later the FCC will throw in the towel and change the rules. The FCC for years wouldn't allow FM on the CB radio band. Now they changed their mind and its OK.

[Sshannon]

18 minutes ago, zzz said:

Does that mean that currently any data transmitted using gmrs today, i.e text messages, are still analog?

No, it’s digital data. That’s permitted in accordance with the regulations, but digital voice is not allowed:

Digital data transmissions. Digital data transmissions are limited to the 462 MHz main channels and interstitial channels in the 462 MHz and 467 MHz bands.

[intermod]

There is always a debate whether digital messaging is analog or digital.  You need to look at the emission designators.  Every DMR voice mobile or portable radio is certified for 7K6F1E, with DMR repeaters additionally certified for 7K6F7E.   

Per § 95.1771 "GMRS emission types", only the following emissions are permitted in GMRS:

https://www.ecfr.gov/current/title-47/section-95.1771

A1D, F1D, G1D, H1D, J1D, R1D, A3E, F3E, G3E, H3E, J3E and R3E

Note the DMR emissions F1E and F7E are not in that list. 

On the issue of text data - you will find the radios that send messaging will be certified for one of the twelve emissions above, and its explicitly permitted.    § 95.1731(b) "Permissible GMRS uses":

https://www.ecfr.gov/current/title-47/section-95.1731

"(b) Digital data.  GMRS hand-held portable units may transmit digital data containing location information, or requesting location information from one or more other GMRS or FRS units, or containing a brief text message to another specific GMRS or FRS unit."

 

[KAF6045]

2 hours ago, Sshannon said:

No, it’s digital data. That’s permitted in accordance with the regulations, but digital voice is not allowed:

Digital data transmissions. Digital data transmissions are limited to the 462 MHz main channels and interstitial channels in the 462 MHz and 467 MHz bands.

Also note that these are SIMPLEX frequencies -- digital data is not permitted on repeaters.

 

[zzz]

1 minute ago, KAF6045 said:

Also note that these are SIMPLEX frequencies -- digital data is not permitted on repeaters.

 

Ahh. Thank out for pointing that out.

[Sshannon]

On 2/22/2023 at 12:20 PM, intermod said:

There is always a debate whether digital messaging is analog or digital.  You need to look at the emission designators.  Every DMR voice mobile or portable radio is certified for 7K6F1E, with DMR repeaters additionally certified for 7K6F7E.   

Per § 95.1771 "GMRS emission types", only the following emissions are permitted in GMRS:

https://www.ecfr.gov/current/title-47/section-95.1771

A1D, F1D, G1D, H1D, J1D, R1D, A3E, F3E, G3E, H3E, J3E and R3E

Note the DMR emissions F1E and F7E are not in that list. 

On the issue of text data - you will find the radios that send messaging will be certified for one of the twelve emissions above, and its explicitly permitted.    § 95.1731(b) "Permissible GMRS uses":

https://www.ecfr.gov/current/title-47/section-95.1731

"(b) Digital data.  GMRS hand-held portable units may transmit digital data containing location information, or requesting location information from one or more other GMRS or FRS units, or containing a brief text message to another specific GMRS or FRS unit."

 

And this site explains what those three characters each mean:

http://fcclicenses.blogspot.com/2011/10/fcc-emission-designators-what-do-codes.html

TL; DR:  

So, for instance, F1D means

Modulation type: F   Angle-modulated, straight FM,

Nature of modulating signal: 1   Digital, on-off or quantized, no modulation,

Information type: D   Data, telemetry, telecommand

 

[Lscott]

Yes you must check the FCC emission designators.

The confusion stems from how the digital data is modulated.

For digital voice mode, DMR, the transmit frequency is shifted by a fixed offset from the channel center frequency. There are typically two frequency steps above and two below for a total of four frequency steps. This is called 4FSK. The details are found in the standard documents for DMR located here for one.

https://www.etsi.org/deliver/etsi_ts/102300_102399/10236101/02.02.01_60/ts_10236101v020201p.pdf

Scroll down to section 10.2 on page 111 for the frequency offsets used.

Other digital voice modes use slightly different methods but the end results are about the same. Here are two more common ones used commercially. 

NXDN:

https://docplayer.net/55804826-Nxdn-nxdn-technical-specifications-part-1-air-interface-sub-part-a-common-air-interface-nxdn-ts-1-a-version-1-3-november-2011.html

P25:

https://www.qsl.net/kb9mwr/projects/dv/apco25/TIA-102.CAAB-C-2010.pdf

Another method to send digital data involves transmitting a series of "audio" tones, most typically two. This is known as AFSK, audio frequency shift keying.  If you want to look at the technical details a bit more look at the following link.

https://notblackmagic.com/bitsnpieces/afsk/