OpenGD77

Hi all

I've been using MD-390's and the AT-878 with both my high power hotspot (Motorola radio plus STM32-DV) and the usual pi based hotspots. None of my pi based hotspots are clones, they are all genuine boards from DF2ET/DB9MAT etc.

The first thing I found was that the GD77 did not sound at all good in regard audio quality on the high power hotspot - I've never had an issue with any other radios on any of my hotspots. I've now backed the TX Level back to 40 to get good TS2 sound quality. Most of my low power hotspots were fine on TS2 but the other day I heard a conversation on TS1 that was really bad in regards audio quality, I have yet to test that further. I know it's not the radio, all of the local repeaters sound fine, so I'm 99% sure it's a hotspot issue. I just think that the GD-77 is perhaps a little less forgiving, maybe a better radio??

Just wondering if anyone else has found similar. I have 2 GD-77's now and even running stock firmware they have the same "issue" so it's not openGD77 causing this!

Thanks for any thoughts
73
Colin
ZL2FL

Hi Colin,

the GD77 is much more easily overloaded than many other radios, could that be the problem ?

/3,
Ian
DJ0HF/G3ULO

Hi Ian

That could be the case, although even my low power hotspot is not good on TS1 but perfect on TS2. I don't know the answer at the moment but I am close to selling the radios and sticking with my D878. But I really love this firmware, it is a delight to have a radio that operates in a way designed by Hams for Hams

Hi Colin,
Check that TA-Tx is off. the trbo group in nz is a motorola network.
Have you also looked into eth choke on the lead trick to choke the RF off.
Also saw something about the earth on the mic lead - if that's relevant ?

TA-Tx is definitely off, it's only an issue on TS1 for some reason and it's also only an RX problem on the radio, Tx is fine.

I've spent the morning playing around with the DMR TXLevel in the hotspot and at 42 (down from 50) it's reasonably useable so I'm pretty sure it's just an alignment issue. I'm going to try and get my hands on a DM-1801 to compare the two radios, shipping is a bugger of course at the moment. Unfortunately Amazon is out of stock also, so if you know of anyone selling a DM-1801 give me a yell I could be open to swapping a GD-77, I have a second brand new one here that's just had openGD77 installed and that's it

Hi,

ZL2FL wrote: ↑

Sat Oct 03, 2020 9:48 pm

TA-Tx is definitely off, it's only an issue on TS1 for some reason and it's also only an RX problem on the radio, Tx is fine.

I've spent the morning playing around with the DMR TXLevel in the hotspot and at 42 (down from 50) it's reasonably useable so I'm pretty sure it's just an alignment issue. I'm going to try and get my hands on a DM-1801 to compare the two radios, shipping is a bugger of course at the moment. Unfortunately Amazon is out of stock also, so if you know of anyone selling a DM-1801 give me a yell I could be open to swapping a GD-77, I have a second brand new one here that's just had openGD77 installed and that's it

Maybe if you have an accurate frequency counter or a spectrum analyzer, you can first check if it's on frequency.


Cheers.
---
Daniel

Yes I think I'll fire up an sdr receiver maybe with SDR# and see what that tells me - good thinking I could have a play with the TX offset value. Mmdvmcal might be handy too

Although my high power hotspot is a Motorola radio programmed on frequency so it should be accurate, but exhibits the same symptoms.

Appreciate the thoughts though team, keep them coming!

I've found the frequency calibration of the radios is not super important.

Of my 8 DMR radios, I calibrated them all to within a few hundred Hertz of each other, but...

My DM1801 won't access my hotspot.

If i change the freq offset in the hotspot however, I can access it with the DM1801, but not with the other radios, including my RD5R

I think there is some undocumented calibation parameter, which we don't use, but the DM1801 and RD5R do use.

However, since the GD77 doesnt seem to use that parameter, its really hard to know what the parameter is or what it changes in the hardware configuration of the radio.

But.. This is not a problem on the GD77, so probably not related to your problem.


As someone else also pointed out, the Rx in the GD77 does not handle strong signals very well. The MD380/390 has a completely different Rx system which is a lot more selective and also handles strong signals a lot better.

But the AT1846S chip in the GD77 etc does not have RF gain control, and there isn't any gain control on the Rx pre-amp.

If you really needed the radio to always handle very strong signals, it may be possible to not enable the Rx pre-amp for the band in question, but the radio is not designed to work with the pre-amp turned off i.e there is no bypass on the preamps, hence the Rx attenuation would probably be quite severe

Thanks Roger, I certainly appreciate your input - and of course this awesome firmware that you and the team have designed.

I might experiment a bit more with the hotspots (both low and high power) and see if I can figure out the magic formula. I really like the way OpenGD77 works and it's near perfect on TS2, which is what I use 99% of the time anyway, so I certainly won't be giving up on it!

73
Colin