I recently spoke with a fellow who was trying to use his hotspot on a frequency around 438 MHz. He wasn’t having much luck and with good reason. The MMDVM firmware blocks usage on all frequencies between 435 and 438 MHz. The block was implemented because 435-438 MHz is a suband used by the amateur satellite service and some amateurs noticed an increase of terrestrial interference with satellite communications.
Another ham that I spoke to is using a hotspot frequency that is also the input of several coordinated repeaters in my area. This is also not a good idea as it can also create interference, especially when operating a hotspot while mobile.
Here is my list of recommended simplex hotspot frequencies that is not likely to cause interference to other operators, repeaters, or satellites:
Most hams seem to set the admit criteria on their radios to Always for use with simplex hotspots. I strongly recommend that you use Channel Free instead to reduce the possibility of doubling.
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
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.
I’ve spent a couple of months chasing down this issue, reading post after article on this subject. The consensus so far has been:
1) Update to the latest firmware. 2) Run the MMDVMcal procedure to minimize the BER. 3) Set the DMR preamble time on your radio to 960 ms.
After weeks of poor results, I came upon the solution that has worked for me (and for others) in a manual for the Anytone 878 produced by Bridgecom. Bridgecom recommends a DMR preamble duration of 100 ms.
1) Update to the latest firmware. 2) Run the MMDVMcal procedure (or enter the sticker offset values for RXOffset and TXOffset). 3) Set the DMR preamble to 100 ms.
Well, I was testing on an Alinco MD-DJ5, a radio very similar to the Anytone 878. So I tried the preamble setting (called Wake Head Period in my software).
I have now achieved the mystical “five 9s” of reliability. I press PTT, I talk, my transmission gets received.
Ah, the sweet smell of success… And kudos to Bridgecom for the level of support that provide for Anytone 878 users.
This solution has worked so far with an Alinco DJ-MD5, a Motorola XPR, and a CS-700 (where I had to use 120 ms because the dropdown increments in steps of 60.). Oddly, my Hytera PD-365 does not support values lower than 360.
I managed to get my hands on one of the hot items in the MMDVM world — an N5BOC Duplex Hotspot. This is really a mini-repeater which uses both timeslots on DMR and has a separate transmit and receive antenna connector. Initial results have been as expected — excellent!
My idea was to have a hotspot where I could configure XLX on TS1 and Brandmeister on TS2. With the N5BOC board and Pi-Star this was a breeze. The key is in the DMR Gateway configuration.
If you’re not currently using DMRGateway, make sure that you have activated it by setting the DMR Master on the configuration page to DMR Gateway. This will reveal options to help you manage Brandmeister, DMR+, and XLX, all on the same hotspot.