OpenGD77 - Repeater

Suggest new features here
G0FHM
Posts: 17
Joined: Mon May 14, 2018 8:47 pm

Re: OpenGD77 - Repeater

Post by G0FHM » Mon Oct 14, 2019 12:58 pm

Hi Andrew,

Pistar supports the GD-77 as a hotspot (Programming cable from radio to USB on the Pi), with the OpenGD77 firmware.

I have both GD-77's plugged in at the moment, and one is a mirror of the other one currently, so they aren't linked to avoid looping and disrupting any network.

If any member of the dev team wants to SSH in and have a poke around to see what is what, then PM me and i'll give you the IP.

Thanks,

J

PS, I do have a dual board here that I can hook a couple of mobile radios to, but i'm on a tight budget, and would rather not have to shell out on a pair of Motorola radios, which tend to hold their value fairly well! GB7GS is now in the vetting system, and it's going to be a low power repeater (10w ERP) to boost the eastern flank of GB7PE (When it comes back) and to give DMR to the Fens while PE is off. I can achieve the ERP by 1w out, so hopefully things won't get too hot. I have had 1x GD-77 running 1w into a dummy load for a while now, linked to BM & DMR+ simultaneously (so it is rarely quiet), and thermal stability seems to be ok.

User avatar
kd2lh
Posts: 30
Joined: Thu Aug 22, 2019 3:26 pm

Re: OpenGD77 - Repeater

Post by kd2lh » Mon Nov 11, 2019 2:40 pm

Roger Clark has been making steady progress on his OpenGD77 firmware for the Radiooddity GD-77 HT. It is now in beta testing, and is supporting tier 2 DMR. It's in limited Beta distribution while the code is stabilized:

http://rogerclark.net/opengd77-hotspot-mode/

To be clear, this solution uses the GD-77's radio hardware and runs his ported version of MMDVM within the radio itself.

When the GD-77 is plugged into the Raspberry Pi using the USB cable (same as used for CPS programming) Roger's community firmware switches into HotSpot mode (it's simplex only). He currently configures Pi-Star as using one of the "Zumspot" family of hotspots (he specifically used "Zumspot Libre USB" for configuring the Modem type in Pi-Star.

I'd like to see "Open GD77" added to the modem types table available in PiStar with the device description "Open GD77 HotSpot" as the description that is displayed in Pi-Star's dashboard and admin left sidebar.

This solution completely replaces the SDR radio components in boards like the JumboSpot "HsHat" with a 5 watt transmitter and radio receiver running MMDVM firmware within the GD-77 HT radio. It's pretty slick, and I expect we'll see this become a viable and even preferred choice for event hot spots as Roger's firmware reaches maturity.

User avatar
kd2lh
Posts: 30
Joined: Thu Aug 22, 2019 3:26 pm

Re: OpenGD77 - Repeater

Post by kd2lh » Tue Nov 12, 2019 2:46 am

I just checked R4.1.0 RC6 with the latest updates, and OpenGD77 is listed as a modem option. Thanks!

G0FHM
Posts: 17
Joined: Mon May 14, 2018 8:47 pm

Re: OpenGD77 - Repeater

Post by G0FHM » Tue Nov 12, 2019 7:29 am

Yes, i've been using it for quite a while now!

IZ4FXT
Posts: 9
Joined: Tue Jun 19, 2018 11:11 am

Re: OpenGD77 - Repeater

Post by IZ4FXT » Fri Nov 15, 2019 11:16 pm

I'm very interested also, in the possibility of connecting two gd77's acting them as a standard not-too-low power repeater!
Coming from two HS Dual Hats, very bad in receiving (yes, worse than the 20mW on TX!!!).

I just leaved a comment in Roger Clark blog asking for that, He and his friends are making some good steps in tier2 mode that is necessary for the repeater mode.
I think pistar also has to be part of the work, having to split the rx side to another usb than tx side, so I'm writng also here.
Thank You in advance
Stefano IZ4FXT

BTW: still nothing about an "openMD380" firmware with hotspot (repeater?) mode?

User avatar
kd2lh
Posts: 30
Joined: Thu Aug 22, 2019 3:26 pm

Re: OpenGD77 - Repeater

Post by kd2lh » Tue Feb 25, 2020 5:11 pm

The main problem with trying to create a duplex repeater out of a pair of Tier 2 capable OpenGD77 hotspots is the hardware synchronization needed between the receive and transmit radios.

There isn't a convenient way to perform that synchronization, and no really possible way to do it with the connections offered on the stock GD77 radio.

Synchronization is needed so that both time slots can be managed discretely since one slot can be receiving at the same time that the other is transmitting. You have to maintain coherence between the two slots.

User avatar
kd2lh
Posts: 30
Joined: Thu Aug 22, 2019 3:26 pm

Re: OpenGD77 - Repeater

Post by kd2lh » Mon Mar 02, 2020 4:54 pm

A quick update. Things in the OpenGD77 hotspot mode are stabilizing nicely. CWID is implemented as is the "CAST" style of display of things like the node's IP address on the GD77 radio's display.

I've been operating for a long time at 1 watt of output, and have just increased the node to 2 watts out. I'm concerned about the potential for problems running the transmitter at continuous duty as a hotspot node at the highest possible power (5 watts on UHF) because Radioddity could not get a response to questions in this area from their development lab in China. That said, others on the GD77 forum indicate they have been operating at full 5 watt power for long periods of time (I don't know of the activity level), and the 50% duty of two slot DMR helps reduce heat. I can feel heat dissipation at 1 watt when things get busy.

One thing to address is RF induction into the USB cable that runs between the Raspberry Pi you're using and the GD77 radio on it's charger. Even at one watt, with an unshielded Raspberry Pi W I was experiencing USB errors that lead to the node shutting down. This seems to be solved now by installing ferrite chokes on both ends of the USB cable, and using a metal case on the Raspberry Pi. So far, even at 2 watts with the Pi next to the radio's charger I have not had any problems with days of up time.

The hotspot mode of the OpenGD77 code is a remarkable piece of development work. One of these nodes can operate for an event at a couple of watts of power, extending coverage. It also uses a receiver with Automatic Frequency Control which eliminates problems when radios are a few hundred cycles off frequency. Because of this, the RXOffset and TXOffset don't need to be configured (they stay "0"). Because of the radio's capabilities, the nodes are necessarily DMR only.

Locked