Troubleshooting Inconsistent DVMega Behavior

DV-Mega Single / Dual band Hat for the Raspberry Pi
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Troubleshooting Inconsistent DVMega Behavior

Post by N8JDM » Mon Apr 08, 2019 12:19 am

Hello all - does anyone have any tips on troubleshooting/tuning a DVMega board used in a simplex hotpost? I have a brand new DVMega Pi-Hat (from Gigaparts so it should be "genuine"). However the performance of the hotspot is poor at best, especially on D-STAR. It seems to take multiple attempts at transmitting into the hotspot for it to do anything. For example, I can transmit up to five times to CQCQCQ before the system responds. If I try to change commands, for example to send ^^^^^I, I have to repeat the same process. DMR responds quicker in that I usually have to key up only once but sometimes it will fail to respond (tested a lot through Parrot). Once it is responding, I will have arbitrary transmissions mysteriously vanish mid-QSO with no feedback that the transmission failed. I've noted with D-STAR that sometimes I received back the double-quick-beep "error" sound and other times I received nothing back when it's failing to work properly instead of the usual single beep for a successful transmission completion.

I have both the dashboard and a Nextion display up while doing this. Sometimes the incoming RF will not show up in either place, but in most cases the RF is "seen" as received in the Dashboard but nothing will happen. BER is 0.0% for D-STAR and 0.3% for DMR.

I've tried both firmware 3.19 which is what came on the DVMega hat from the factory and 3.26 to see if the referenced D-STAR fixed changed anything and it didn't.

I've also tried 4.0 RC3 to see if that made any difference and it did not.

I also note that pistar-mmdvmcal does not work - claims my radio is unsupported although it successfully identifies it. I've also tried tuning the RXOffset as well as the RX input levels.

I'm out of ideas and looking for some thoughts. Anyone able to assist? Could be a bad board?

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Re: Troubleshooting Inconsistent DVMega Behavior

Post by KE0FHS » Mon Apr 08, 2019 1:50 pm

With your low BER rate for DMR, you shouldn't need to adjust RXOffset.

I mention the following just so you know that you should be able to get really good results from the DVMEGA: I have a DVMEGA-DUAL that was mounted on a RPi 3B, then a 3B+, and now a 3A+, running firmware 3.26 and previously 3.19 (and several firmware versions before that), and Pi-Star 4.0.0-RC3 and previously 3.4.17 (and several upgrade versions before that), and have never experienced anything like what you're describing.

The only things I can suggest in terms of troubleshooting is to make sure your radios are transmitting at their lowest possible power output (I've got my DMR radio set at 0.5 W, and my D-Star radio set at 0.05 W), and to try moving your radios further away from your hotspot, as being too close can desense the hotspot's receiver.

I applaud your troubleshooting tenacity, but if nothing you try solves the issue, at a certain point you may need to conclude that the board itself is defective and return it for an exchange. Like I mentioned, the DVMEGA typically is a very reliable board and normally you shouldn't be having this difficulty.

Good luck!
73, Toshen, KE0FHS
Playing with Pi-Star (unofficial notes about setting up and using Pi-Star):

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Re: Troubleshooting Inconsistent DVMega Behavior

Post by N2MCI » Mon Apr 08, 2019 5:06 pm

I'm not sure this is your problem, but when I got my DV-MEGA about 2 1/2 yrs. ago, my DV-Mega would some times not show up, especially when I would
unplug Hat from the Pi. I looked at the DV-Mega board I noticed 10 Pin connector looked like there were a few cold solder joints. I resoldered all the pins
and have never had a problem since.

Your mileage my vary.

-73, Pete N2MCI

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Re: Troubleshooting Inconsistent DVMega Behavior

Post by N8JDM » Tue Apr 09, 2019 11:58 pm

Thanks for the ideas everyone. Looks like I'm going to try to return it. I'm in contact with where I bought it. For what those boards cost, I hope it's easy to get it replaced.

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