Packet loss when transmitting from GD-73 to GD-77

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W3RED
Posts: 2
Joined: Tue Dec 21, 2021 4:35 pm

Packet loss when transmitting from GD-73 to GD-77

Post by W3RED » Tue Dec 21, 2021 5:05 pm

Initial observed issue: When transmitting from my GD-73 to my GD-77 in hotspot mode, recorded audio from Parrot and from other listeners on a TG hear about 25% packet loss. Imagine if I counted from 1 to 10 and you heard "2-3-5-7-10".

I presumed the issue was with my Pi-Star or its configuration. I Installed newest version of Pi-Star, tweaked RX offset to get BER under 1% (sometimes 0%). Then I started testing different radio combinations.

Transmitting from the GD-73 to the Pi-Star with integrated MMDVM radio does not have this issue.

Transmitting to OpenGD77 Hotspot from other radios does not have this problem.

Transmitting from the GD-73 to other radios does not seem to have the problem.

Transmitting from the GD-73 to the GD-77 running OpenGD77 firmware (not in hotspot mode) DOES seem to suffer packet loss. I did not test transmitting from the GD-73 to the GD-77 running the stock firmware.

My assumption: there is something funny happening when transmitting from the GD-73 to the GD-77, but I don't know if the problem is with any one of those two radios. I don't notice a problem with any other combinations.

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

Re: Packet loss when transmitting from GD-73 to GD-77

Post by VK3KYY » Tue Dec 21, 2021 8:14 pm

When TYT originally launched the GD73, it had very high BER when used with hotspots

TYT initially said the problem was with everyone's hotspots, because their BER test equipment said the radio was OK.
However eventually they were convinced to look at the problem, and they released a firmware update that partially fixed the problem.

When using multiple different cheap radios, the first step is to make sure they are all frequency calibrated correctly.

I initially had problems with my DM1801 not working with my hotspot , but all my other radios were OK.
So I had to adjust its calibration to make sure it was on frequency.

Using a hotspot as the reference is not practical, because the BER value is not an direct measurement if frequency error.


I have a GD73, supplied to me by TYT for testing, but gave up using it, because of these problems.
Coincidentally I pulled the GD73 out of the junk box last week, but I can't update tgye firmware because the firmware loader and even the CPS won't seem to work on Windows 10.

When I get time I will need to get my old Wiindows XP laptop working which hopefully will allow me to update the firmware and load a new codeplug

But until then the GD73 will go back in the junk box

iu2dlc
Posts: 8
Joined: Fri Mar 06, 2020 6:29 am

Re: Packet loss when transmitting from GD-73 to GD-77

Post by iu2dlc » Wed Feb 23, 2022 3:37 pm

Nice to read someone has my same issues [:-((
I wrote te full history on another topic i summarize:
GD77+OpenGD77+PiStar both on Pi3B+ and PiZero 2 W = high BER but no packet loss but i am hard to accept what is not close to perfectiono so briefly i tried in the order:
1) Change the offset of the AT878UVII to +1000Hz leaving GD77,PiStar untouched. Worked with 0.1% BER (good but dirty workaround).
2) Change the offset on PiStar leaved untouched AT878 same as before little bit more tricky but close to 0.2-0.3BER so accettable.
3) Drastically changed to -20 the oscillator value in calibration of GD77 DMR UHF section. Works perfectly with 0/0.01 BER only in TX always 0 in RX (by the GD77 site is the oppostite my RX is it's TX and viceversa). PiStar and AT878 untouched. That's the final solution for my setup. It works even if i clear understand that changing the calibration parameters shouldn't be done but considering i use GD77 only for hotspot it can be OK.

All i did on step 1,2,3 i tried in order to make the GD73 works within the described environment. The answer is NO WAY!
Packet loss is huge even when not indicated. Playing with thoose values (1,2,3) i was able to reduce BER but not packet loose and even when ,compared to other qso i eard, packet lost were less than 5% was totally unreadable on the radio yeah like i say (as the friend reorted) "1,2,3,4...10,11 and i can ear only 2,4..,7,9" definitelly funny in a way.

The mistery, at least for me, is that in simplex the GD73 is ok both with the GD77 and the AT878UVII. How come? Also for my trial GD73 worked well on Motorola DR3000 Repeater.
To be honest i gave up after one month because it's over my comphrension. Also i don't have measurement tools and ,even if, gd73 is "melted" with the antenna so it's impossible to test due lack of RF connector unless you open and "try-to-destroy" it :-)))

At this point i'm only curious if someone found the reason and eventually solved it. Just curious because due the gd73 limits (no internal db,only pc programing) i rather prefer using the serious AT instead.

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