DCDM and SFR

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YT5HOK
Posts: 213
Joined: Sat Nov 16, 2019 11:36 am
Location: Belgrade, KN04FR

Re: DCDM and SFR

Post by YT5HOK » Fri Jan 21, 2022 6:26 pm

Short answer: No.

Long answer: search this forum.

Cheers!

VK3KYY
Posts: 7478
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: DCDM and SFR

Post by VK3KYY » Sun Jan 23, 2022 9:53 pm

ecutino wrote:
Sun Jan 23, 2022 9:41 pm
Short reply: unfair

Long reply: unclear and unexplained

Elio - IZ2RLJ

PS: we are (should be) hams in order to share and explain ideas. Enjoy.
Please read the forum.

The hardware can't support SRF, the transcrieiver chip can't support switching between Tx and Rx fast enough.

DCDM is not supported because no one has the time to reverse engineer the official firmware and write an implementation for this.
There is no documentation / data sheet about how to configure the DMR chip for DCDM

The source code can be downloaded from here

https://www.opengd77.com/downloads/rele ... and_tools/

for anyone to work on and develop new features

ok1pt
Posts: 167
Joined: Mon Jul 20, 2020 3:38 am

Re: DCDM and SFR

Post by ok1pt » Mon Jan 24, 2022 6:32 am

Hi!
I tested GD77 with orig firmware about a year ago together with Anytone 578/878. The DCDM feature was barely usable, GD77 had problems to maintain the time slot sync, it often drifted in time and started to interefere with the 2nd timeslot (generated by the Anytone radio). SFR feature (operated on 578) was unusable with GD77 for exactly the same reason. However, even 878 radios had problems to keep the sync for longer transmissions.
The last released software for 578/878 is much better, now the SFR seems to be really perfectly working using the split-timeslot mode. I currently don't have GD77 with original firmware to chek, how is it working with AT stations with the recent firmware, but I'm afraid that it won't be much better than before.
And I believe that driving the DMR chip in the DCDM mode is really complex thing and that it can't be done without complete documentation, which is the biggest problem the developers have. For the same reason we still don't have SMS and it's a big questions, whether it will ever developed in the future.
WIth regards / 73,
Pavel

VK3KYY
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Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: DCDM and SFR

Post by VK3KYY » Mon Jan 24, 2022 10:19 am

Thanks Pavel

I have heard some people on BM saying they are using their Anttone as some sort of range extender for their hotspot, so I presume they must be using SFR mode.

It is a shame the GD77 hardware is not capable of this, but its impossible to do things the hardware is incapable of doing

It may be possible to develop SFR for the MD9600 because it does not use the same RF chip, and swithing from Tx to Rx to Rx etc may be faster.

ok1pt
Posts: 167
Joined: Mon Jul 20, 2020 3:38 am

Re: DCDM and SFR

Post by ok1pt » Tue Jan 25, 2022 4:44 am

VK3KYY wrote:
Mon Jan 24, 2022 10:19 am
Thanks Pavel

I have heard some people on BM saying they are using their Anttone as some sort of range extender for their hotspot, so I presume they must be using SFR mode.

It is a shame the GD77 hardware is not capable of this, but its impossible to do things the hardware is incapable of doing

It may be possible to develop SFR for the MD9600 because it does not use the same RF chip, and swithing from Tx to Rx to Rx etc may be faster.
I'm not sure they use the SFR mode, because hotspots are transmiting on both timeslots, so it's impossible to use any kind of DCDM mode including SFR with them.
However, AT-D578UV can do more magic than just SFR, it can do cross-band repeater either in FM or in FM/DMR mode, so it's a way to use it as an extender - operate one channel on the hotspot and the other on the opposite band in FM and utilize the x-band repeat function.

SFR on the MD9600 would be really interesting and exciting thing! Is the hardware documentation available ?

With regards / 73, Pavel

VK3KYY
Posts: 7478
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: DCDM and SFR

Post by VK3KYY » Tue Jan 25, 2022 9:08 pm

The MD9600 uses the C6000. There is not any additional information for this on the MD9600

But SFR is just listening on one TS, then putting the Rx data into the Tx and tell the C6000 to transmit that data on the next TS

I tried some experiments to do this on the GD77 but the result was that the audio on the Tx sounded bad

The audio was intelligible but with many R2D2 type beeps

I think the problem is that when RX is enabled , there is no audio for perhaps 5 or more milliseconds, so the beginning of every DMR frame is lost.

The RF chip in the GD77 is literally a $1 chip designed for cheap Beofeng CB etc radios, and not for DMR.

I think the Anytone radios use a newer version of the same chip, also Anytone use 2 of these chips in ecah radio and use some new secret functions in this new version.
There is no official documentation for this RF chip, even the old version, except some old incomplete data sheet.

So attempting to use it for functionality it is not designed for, is effectively impossible

G4EML
Posts: 919
Joined: Sat Nov 16, 2019 10:01 am

Re: DCDM and SFR

Post by G4EML » Wed Feb 02, 2022 10:59 am

Single frequency repeat is available as an additional cost option on the latest Motorola repeaters. Retevis also market the RT74 repeater that has single frequency repeat capability. So the equipment is out there and available at a cost.

The DMR specification does acknowledge that SFR is possible but it does not specify exactly how it is implemented. That seems to be proprietary information. From the information I can find it seems that these repeaters will only work (correctly) with compatible radios from the same manufacturers. For a commercial system that is not a big problem but for amateur radio use it is.

There are a few amateur SFR systems in operation but I don’t have any direct experience of them. Especially how compatible they are with multiple brands of radio.

It would be nice to be able to implement some form of SFR into OpenGD77 but unfortunately we have done some experiments and it appears that the hardware in the GD77 is unable to operate fast enough to achieve this. We have yet to do similar experiments with the MD9600 but it may also be the same story there. The commercial repeaters have the benefit of having totally separate receivers and transmitters which can be operated simultaneously. Both the GD77 and the MD9600 share some hardware between receive and transmit and so need to be switched between the two states, that takes time and there is only 1ms available between the two timeslots.

Colin G4EML

9A3BKR
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Joined: Tue Jun 02, 2020 10:25 pm

Re: DCDM and SFR

Post by 9A3BKR » Sun Jan 15, 2023 3:54 pm

Sorry to bring up this top after a year of inactivity.
I would like to use my OpenGD77 radio on a single frequency repeater. Were there any advances in the firmware that would allow the use on a SFR with good audio? Any particular settings or programing that would make it possible?

Kris - 9A3BKR

G4EML
Posts: 919
Joined: Sat Nov 16, 2019 10:01 am

Re: DCDM and SFR

Post by G4EML » Sun Jan 15, 2023 6:44 pm

There doesn't seem to be a single standard for single frequency repeaters, it seems like each manufacturers has a slightly different implementation. Possibly for this reason there are relatively few of these in amateur use.

So the short answer is no, there has been no effort put into getting OpenGD77 to work with a SFR. As far as I am aware none of the developers has a SFR available to test with.

Colin G4EML

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