How do I make a digital repeater?

[G4EML]

What you are asking for is a single frequency repeater.
OpenGD77 cannot do this.

In theory it might be possible but it would need a lot of experimenting and development.
No one has the time or knowledge to do this at the moment.

[VK3KYY]

Thank you for your answers Mr. G4EML

I plan to try to implement this, but its not easy, and there are many other things that are higher priority.

Your diagram also looks like you expect 2 radios to be linked together, but this is not necessary.
The normal operation is for the same radio to both receive and transmit.




BTW.

Do you have a callsign?

[VK3KYY]

What you are asking for is a single frequency repeater.
OpenGD77 cannot do this.

In theory it might be possible but it would need a lot of experimenting and development.
No one has the time or knowledge to do this at the moment.

Colin.

BTW.

What I don't understand is how the receiving radio decides which TS to listen to.

I think the OpenGD77 currently can't listen to the output of duplex repeater when its set to simplex operation ( because the Rx and Tx frequencies are the same).
I just tested and I can listen to the input of my duplex hotspot, as the transmitting radio is just transmitting on one TS.

But when try to listen to the output of my duplex HS, its random whether I hear any audio, because its only listening on one TS, an that DMR mode, it is not looking for a TimeCode, because one is not sent in Simplex.

I think other commercial radios can listen to the output of repeaters, so there must be a way to do this. But the HRC6000 code will need to be modified

And, for SFR I don't know how to set the transmission TC.

There is something in the data sheet about the "Active" TS, but its not clear what that means

[G4EML]

In normal operation a mobile set will use a defined sync pattern embedded in the centre of the data burst. A base station (repeater) will use a different one. The sync pattern is used to synchronise the receiver so the receiving device needs to be looking for the correct pattern.

In direct mode (simplex) both mobiles use the mobile sync pattern. This is the same for both timeslots so a receiver cannot identify which is which.

Dual capacity direct mode mobiles use different sync patterns for the two Timeslots. The receiver can then identify which is which and synchronise accordingly.

A Single frequency repeater (and all of the mobiles) need to use dual capacity direct mode so so that the timeslots can be kept separate.

I believe the C6000 chip can be set to recognise (and generate) the different sync patterns.

So before SFR is possible we would have to get DCDM working. There is more to it than just changing the syncs though. All radios need to keep in sync with each other all the time and need to negotiate a master radio which send out regular beacons to achieve this. It is quite a complicated process which I don’t fully understand at the moment.

[VK3KYY]

In normal operation a mobile set will use a defined sync pattern embedded in the centre of the data burst. A base station (repeater) will use a different one. The sync pattern is used to synchronise the receiver so the receiving device needs to be looking for the correct pattern.

In direct mode (simplex) both mobiles use the mobile sync pattern. This is the same for both timeslots so a receiver cannot identify which is which.

Dual capacity direct mode mobiles use different sync patterns for the two Timeslots. The receiver can then identify which is which and synchronise accordingly.

A Single frequency repeater (and all of the mobiles) need to use dual capacity direct mode so so that the timeslots can be kept separate.

I believe the C6000 chip can be set to recognise (and generate) the different sync patterns.

So before SFR is possible we would have to get DCDM working. There is more to it than just changing the syncs though. All radios need to keep in sync with each other all the time and need to negotiate a master radio which send out regular beacons to achieve this. It is quite a complicated process which I don’t fully understand at the moment.

Thanks

That sounds complicated...

I don't think its necessary to actually support DCDM its own right, because from what I understand, DCDM is designed so that multiple MS stations can communicate on the 2 different TS without a repeater, and this would be overkill for amateur radio as we are not short of frequencies.

I was in touch with one of the RAYNET groups in the UK, who were using a Hytera handheld with the SFR option installed, because they told me that the official GD77 firmware was not compatible with the Hytera in SFR mode, because the official firmware seemed to be receiving on the alternate TS from the it was transmitting on, while in simplex mode.

This caused feedback via the speaker to mic path in the GD77.

I presume they had tried the various DCDM options on the GD77 and couldn't get it to work whatever they tied.

I'll see if I can find the email address of whoever it was that emailed me, but it was getting on for 2 years ago, and I may not be easy or even possible for me to find who it was.


I can however capture the C6000 data when the official firmware is in DCDM mode and this may give a clue about what commands are associated with the sync pattern etc.


But even before that. I would need to to modify the firmware, so that I can switch between TS when receiving signals which are on both TS.
i.e Radio A and the SFR Radio (B)

One of the members of my local radio club seems to work in the mobile radio industry, so he may have access to a SFR radio, but I think the chances are quite low.

[G4EML]

It might be possible to make a simpler system but it would then probably only work with OpenGD77 radios. It would not then be compatible with other brands.

One of the problems would be that the current firmware does not maintain the timeslot timing in the absence of an incoming signal. It falls back to an out of sync condition when not receiving. DCDM requires all participating radios to keep in sync all of the time so that when they transmit they know at what time to key their transmitter.

I think the C6000 can do this by using the timeslot interrupt but the current code would need to be changed to remain in a synchronised state even when not receiving. Synchronisation is maintained on a quite channel by the master radio sending out a short burst every 4.5 minutes. The radios are expected to maintain sync between bursts by their internal clocks.

In a SFR system all portable radios always transmit on slot1. The repeater always receives on slot 1 and relays on slot 2. The portable radios receive on both slots and pick the strongest signal. In that way the use of the repeater is transparent to the user. They may be receiving direct from another user or via the repeater, whichever is strongest.

[VK3KYY]

OK.

Someone told me about the sync master stuff, but I'd not considered it for the OpenGD77

Strangely I was told that the firmware already works with a Hytera SFR