Month: August 2019

Duplex Hotspot Reliability Solution

So you’ve bought a new duplex MMDVM hotspot such as the one from N5BOC. You want to experiment with different DMR networks on each of the timeslots. You’ve set the recommended offset values in the MMDVM Expert settings. Yet every third or fourth PTT press results in a lost transmission. You’re so frustrated you want to throw your radio and hotspot across the room. Sound familiar?

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.

73

Greek Pirates on the AM Band

When I travel to other countries, I try to take out a few minutes to scan the AM broadcast band. I have observed that over the past few years I am hearing less and less. Sometimes there is nothing to hear but static and local noise. Many counties are completely abandoning AM broadcasting in favor of FM and digital (DAB). The urban environmental interferance levels don’t help things either.

A recent bandscan in Athens provided a nice surprise. The standard AM broadcast band was full of strong signals, most playing music. I settled on a strong station on 828 kHz playing a program of American standards and light fare. There were a few short announcements in Greek but I was listening as I fell asleep, so didn’t catch anything I could remember.

A bit of research the next morning showed that 828 kHz, and most other stations heard on the AM band in Athens, are unlicensed hobby stations. The Greek government does not seem to care much and these stations are providing a service.

If your travels include Athens, don’t forget to bring along an AM radio. You won’t be disappointed.