Motorola DTR and DLR series 900MHz FHSS digital radios

[Lscott]

19 minutes ago, tweiss3 said:

I think any implementation would have to come from Motorola directly, or whichever FHSS radio manufacture you are using. That being said, lets talk about a theory that might work as a repeater.

My understanding is the radios utilize at least 50 frequencies, and hop about 50 times a second. The privacy is caused by changing up the hop set (order and number of frequencies), which means any repeater would have to be programed identically to the radios, but that's not a problem, that's typical of repeaters. Two problems exist, which we have to overcome:

1) At any given time (snapshot), the radios are using a single frequency for both receive and transmit. This could potentially be overcome by having a small delay in the re-transmission, say 2 hops behind the transmitting radio. Any radio in range of the transmitting station would continue to sync and receive from that station, stations outside that range would instead be synchronized and receive from the "repeater" station. Problem solved?

2) Second problem is, a traditional repeater usually has a fixed frequency set, and uses a duplexer to separate receive from transmit to eliminate desense in the receiver. The alternative is two antennas. Since 902MHz is such a high frequency, vertical separation can be relatively small and provide good isolation. 1 foot vertical provides 27dB isolation, and 2 feet increases that to 39dB, more than enough decent selectivity can overcome.

Make sense? I think the theory would work, practice might be a bit harder to accomplish. There there is getting 15C certification for the "repeater".

That might work for a large site. However if one wanted to install a private repeater for family use it doesn't look practical. Also as far as I know there is no open standard for FHSS radios so any implementation would be proprietary and the manufacture likely wouldn't be all that interested in opening it up or licensing the technology. So further along that line if another manufacture sold FHSS radios they probability they would work with another manufacture is nearly zero. That's why an open public standard or one that is open to licensing is much preferred.

[gman1971]

@Lscott

There is an FHSS DTR repeater... I don't remember who makes it, but I know at least one exists. 

Then there is the fact that everything is narrowband, and only things in the 2.4 ISM bands use this type of spread spectrum tech. Not much demand for an FHSS repeater. 

The repeater would use the two codes like PL tones, one for input, one for output.

G.

[gman1971]

2 hours ago, Lscott said:

That might work for a large site. However if one wanted to install a private repeater for family use it doesn't look practical. Also as far as I know there is no open standard for FHSS radios so any implementation would be proprietary and the manufacture likely wouldn't be all that interested in opening it up or licensing the technology. So further along that line if another manufacture sold FHSS radios they probability they would work with another manufacture is nearly zero. That's why an open public standard or one that is open to licensing is much preferred.

You can stick to NXDN if you don't like FHSS... and BTW, you are basically quoting what I've already stated on the other thread you abandoned: There needs to be an open standard for FHSS to work, otherwise it won't make much sense, and at that point its better stick to what you have that works for you.

 

G.

[tweiss3]

I found it. It only "doubles" the range in 1 direction, and they use 20' of separation which gives 47dB of isolation. It is not bi-directional, so it is kind of a pain in the rear, and won't help most situation, but what do you expect from license-free solutions.

[Lscott]

7 hours ago, gman1971 said:

You can stick to NXDN if you don't like FHSS... and BTW, you are basically quoting what I've already stated on the other thread you abandoned: There needs to be an open standard for FHSS to work, otherwise it won't make much sense, and at that point its better stick to what you have that works for you.

 

G.

It’s not a question of what I like. More like what fits the application given the limitations. For example with GMRS you only have 22 simplex channels and out of that 7 are limited to just 1/2 watt unless the FCC allows more power for digital, which is possible I guess. That leaves just 15 frequencies, not a big hop set otherwise.
 

I’ve also been looking at some of the testing and research for a “possible” move to digital voice on the VHF marine band. I believe that’s on the docket for the WRC23 conference. Apparently TDMA voice modes like DMR and TETRA are not being recommended. They are leaning to systems using FDMA. One that I saw mentioned was dPMR.

While some like DMR, don’t get me wrong I like it too and have been looking at getting a few more radios (NX-1300DU which I don’t have in my collection for example) and I do have a few XPR6550’s. I read some interesting comments about DMR not being a huge favorite of frequency coordinators particularly when 6.25KHz channels are in the area and they need to assign additional ones. The reasons mentioned were some I never considered before.

And yes I’m aware of the long thread on digital modes back in 2021. I even made a few posts to that thread myself towards the end. Funny thing is nobody seemed to mention spread spectrum technology that I recall.

[Radioguy7268]

7 hours ago, gman1971 said:

@Lscott

There is an FHSS DTR repeater... I don't remember who makes it, but I know at least one exists.

Cane wireless makes an FHSS repeater setup for DTR radios - http://www.canewirelesspro.com/drx-repeater.html

I've never sold one or played around with one, but looks like about a $3000 solution. Need to buy two of their boxes, and separate them with at least a 20 ft length of ethernet cable connecting the two boxes.

It appears to be bidirectional to me. One DRX radio receives a particular talkgroup/code - then the 2nd DRX radio re-transmits on a different group. It appears that you would need to have a portable DTR that's set up to scan talkgroups in order to talk back & forth.

[Lscott]

At $3K not exactly cheap and you still need two antennas with feed line and space to mount the separated antennas.
 

So apparently the repeater is really two separated independent FHSS radios that exchange the digital audio using a fast Ethernet link. Since you can’t use cavities to isolate the TX and RX you need the physical separation between the antennas to provide the necessary isolation.

Calling it a repeater is sort of stretching the definition a bit. It looks more like two independent network connected radios.

[Lscott]

People might find this an interesting reference to read.

 

R-HDB-24-1996-PDF-E.pdf

[gman1971]

Well, its still a repeater, even it has limitations...

I think it can be done, but given the plethora of digital formats and modulations already in existence, throwing one more in the mix might not make much sense... we'll see.

G.

[PACNWComms]

On 7/1/2022 at 11:54 AM, gman1971 said:

@Lscott

There is an FHSS DTR repeater... I don't remember who makes it, but I know at least one exists. 

Then there is the fact that everything is narrowband, and only things in the 2.4 ISM bands use this type of spread spectrum tech. Not much demand for an FHSS repeater. 

The repeater would use the two codes like PL tones, one for input, one for output.

G.

There is a "Range Extender" version and then another standalone repeater available for the DTR series Motorola radios. https://www.twowayradio.com/motorola-dtr-range-extender.html

The standalone is the CW-DRX1020 repeater. There used to be a third company making these, back a decade or so when the DTR series first came out, none were Motorola, but the first one I used looked like a MotoBridge system. It required a "donor" DTR series radio and could only extend a specific TalkGroup, so one repeater per TalkGroup. Not very cost efficient of an option, and the DTR410/550/650 were only one watt output, so the range expectations were not very far to begin with. I still have several schools using DTR series radios a decade after implementation, no repeater needed for a campus about half a mile across. 

Some large warehouses had the repeaters, but may not be using the radios as they complained about not being able to get "cell phone" batteries any longer. I told them to buy BL-5C batteries, as they said range was less due to poor battery performance.

So, I know of three repeaters that worked with the Motorola 900 MHz ISM band FHSS radios. With two still being available. Might be useful for those using the DTR series, not sure about newer version DPL, etc. though, have no experience using those.

[WRKC935]

So I may have missed it, but are the old Nextel phones OOB direct connect and the DTR radios compatible and able to talk to each other?

Running around in public with a 'working' NEXTEL phone would be interesting as that system has been gone for years now.  Beyond that, if compatibility exists, it provides a source of radios that work with the DTR stuff that are cheap and available.

 

[Radioguy7268]

The Nextel 3rd generation (last generation?) phones had a built in FHSS 900 MHz "off network" radio they called Direct Talk. It is NOT compatible with the DTR/DLR series of Motorola radios, even though it's the same technology. Not sure what in the protocol was different, but I'd imagine it's beyond a simple secret hopset number, or else that info would have leaked out to the public by now.

There were a few Nextel phones like the i375s which had an external antenna and were ruggedized. Those seemed to be the units with better range on 900 MHz Direct Talk, but I never did a side by side range test with DTR series vs. the Nextel models.