Compatibility issue between DM-1701s in hotspot mode ?

[HA7LCA]

Hello everyone,

I need some help. I have a Baofeng DM-1701 set up as a high-power hotspot with the latest openGD77 firmware, connected to a roof antenna. It works perfectly, I can use it for radio communication from almost anywhere in the city.

I got another DM-1701 radio. If I leave the factory firmware on it, everything works great—it communicates in all directions, sounds clear, etc. But if I install openGD77 on it as well, then when using the high-power hotspot, which is also a DM-1701, the reception is very noisy, choppy, and almost unintelligible. There is no problem with transmission; they hear me perfectly.

If I swap the roles of the two radios (using the other one as the hotspot), the situation is the same.

However, if I use a classic small MMDVM hotspot modem, the transmission is excellent both ways on all TGs. The BER is 0.2 in all cases.

Other radios (Alinco, Hytera) have no problem with either hotspot. Both Baofeng DM-1701 radios also work well with other radios in simplex (digital/analog) on their own.

Conclusion: Under openGD77, the two Baofeng DM-1701s do not seem to like each other when one of them functions as a high-power hotspot. Does anyone have similar experience or any suggestions?

Thank you very much!

[VK3KYY]

Hello everyone,

I need some help. I have a Baofeng DM-1701 set up as a high-power hotspot with the latest openGD77 firmware, connected to a roof antenna. It works perfectly, I can use it for radio communication from almost anywhere in the city.

I got another DM-1701 radio. If I leave the factory firmware on it, everything works great—it communicates in all directions, sounds clear, etc. But if I install openGD77 on it as well, then when using the high-power hotspot, which is also a DM-1701, the reception is very noisy, choppy, and almost unintelligible. There is no problem with transmission; they hear me perfectly.

If I swap the roles of the two radios (using the other one as the hotspot), the situation is the same.

However, if I use a classic small MMDVM hotspot modem, the transmission is excellent both ways on all TGs. The BER is 0.2 in all cases.

Other radios (Alinco, Hytera) have no problem with either hotspot. Both Baofeng DM-1701 radios also work well with other radios in simplex (digital/analog) on their own.

Conclusion: Under openGD77, the two Baofeng DM-1701s do not seem to like each other when one of them functions as a high-power hotspot. Does anyone have similar experience or any suggestions?

Thank you very much!

Check the frequency calibration of those 2 radios

[HA7LCA]

• It works properly in simplex mode.

• It works properly with the factory firmware.

• It works properly with other radios.

(DMR is particularly sensitive to frequency drift, so if it were off, there would be issues with other radios as well. The Hytera is especially sensitive, and it works fine with that.)

The problem only occurs when both radios have openGD77, and ONLY on the receiving side. Transmission is fine, I'm heard well, and since it's simplex, I don't think there's any drift. Could it be a filter that needs to be turned on/off? I don't know.

[HA7LCA]

Correction!
I put the factory firmware back, and the reception is still not good if both the hotspot and the client are Baofeng DM-1701 radios.

[VK3KYY]

Correction!
I put the factory firmware back, and the reception is still not good if both the hotspot and the client are Baofeng DM-1701 radios.

Please check the frequency calibration.

I know you don't think this is the problem, but to be scientific you have to check each possible cause and only dissmiss it after it has been checked

You don't need a frequency counter. Just a SDR zoomed in as much as possible, and transmit in the calibation screen, as this has no FM modulation, hence its much easier to see the frequency on the SDR.

It's also possible that there is a fault in one or both of your DM1701.

DM1701 build quality seems to be lower than TYT radios

[HA7LCA]

Alright, I understand. I need to get an SDR then, because I don't have one at the moment
Thanks for the advice

[VK3KYY]

Alright, I understand. I need to get an SDR then, because I don't have one at the moment
Thanks for the advice

OK.

SDR is the cheapest way to align the frequencies



If you have multiple DMR radios and one or more hotspots, then it is always necessary to calibrate the frequency of all the DMR radios so that they are the same, Becuase the hotspot frequency tollerance is not good.
e.g. in PiStar to get good BER the frequency offset of the hotspot has to be adjusted to match the radio, and must be very accurate.

Normally DMR radio < ---- > DMR radio , frequency calibration is not as important as for DMR Radio < ------ > Hotspot, but if your DM1701 are perhaps 500Hz or 1kHz different in Tx freq, then it could begin to cause lower quality reception