Duplex Hotspot Reliability Revisited

Last August, I presented a solution for the “lost transmission” syndrome when using an MMDVM duplex hotspot. Several members of the 020 Digital Multiprotocol Group and I remain dissatisfied with our overall user experience. Granted, fewer transmissions are being lost than at first, but overall the number of transmissions during a longer QSO that fail to properly negotiate with the hotspot are higher than we’d like.

Earlier this week, 020 member Scott <KB2EAR> did some further digging and came up with aditional ideas found on the interwebs. I’ve taken these recommendations, added some others, and tested extensively. Here is my new set of recommendations for MMDVM duplex hotspot reliability when using DMR. This supersedes my article from August 29, 2019.

1) Update to the latest firmware.
2) Run the MMDVMcal procedure to minimize the BER
3) Set the MMDVMHost modem TXDelay=50
4) Set the MMDVMHost modem DMRTXLevel=55
5) Set the MMDVMHost DMR TXHang = 20
6) Turn off any mode other than DMR to avoid protocol scanning negotiation
   issues.

I withdraw my earlier recommendation to reduce the DMR preamble. After much consideration, it seems to be unnecessary, with no clear benefit.

So far, using these setting on 2 different N5BOC duplex hotspots have yielded excellent results and reliability. Negotiation failures are now the rare exception. Tests were conducted with an Alinco DJ-MD5, a TYT MD-380, a CS-700 and a Hytera PD-365. Give these settings a try and let me know how they work for you.

73 de K2IE

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