This will be an overview/review/information tidbit post about an exciting new MMDVM repeater board that just appeared on the market during Dayton 2019.
The Motorola MTR2000 is a modern synthesized repeater/base station (depending on configuration) that debuted around 1997, it is built on a solid, reliable platform and has superior RF performance, RX sensitivity and selectivity and one of the few modern units that can truly live up to the ‘continuous duty’ duty cycle that us amateurs need. Us, along with many others experimenting with Motorola DMR and Yaesu DR-1X repeaters have struggled to keep machines rated as continuous duty on the air. We aren’t going to rewrite the book on the MTR2000, the definitive source for all the info you need is here.
Our friends in Kansas the K0USY group sought a better way to integrate Pi-Hat MMDVM interfaces with the cheap, readily available, and solid performing MTR2000, without the need for an external controller, or wires coming out the back. They developed a STM-32-DVM based controller that plugs neatly into the repeaters card cage (used for Motorola accessory board) in one economical self-contained package.
The board can be ordered with either a Orange Pi Zero or Nano Pi-NEO. We elected to try the Orange Pi-Zero. The device is as close to plug and play as anyone could hope for something so complicated. The whole device was designed from the ground up for the MTR2000, and only requires slight programming changes in the repeater and two audio adjustments. The programming and alignment changes are detailed here. The only thing we have to add is that it was very very easy, no specialized test equipment was needed (but was used just to verify).
From our own testing and talking to others using different model MTR2000’s in different bandsplits, it seems like ALL MTR2000’s (VHF. UHF, High Power, Low Power) will all use an Aux Tx Input level of 20 or 21 with very negligible measurable distance noticed between the two. On the Rx side, discriminator values of 108-112 all provided acceptable results. If using Pi-Star, the built in MMDVMCAL utility is very useful for modulating DMR test signals.
Once your audio settings are aligned you can use the device, ours came with a copy of MMDVM in the non-GUI, CLI (Command Line Interface) format. With the CLI version you simply SSH into the device from a computer on your LAN and setup your MMDVM.ini file as needed. Currently we are using Pi-Star simply because for in-the-shack testing its much faster to work with the graphical interface when testing out various modes and settings. Once we have settled on our finial configuration we will copy our MMDVM.ini settings from Pi-Star to the CLI MMDVM software as it should be more stable.
One of the purposes of this article is to give a few extra insights and tips we haven’t yet seen mentioned in other articles online. One such item is that in your MMDVM.ini (On Pi-Star Configation -> Expert -> MMDVMHost) for DMR you need to set your TXDelay to 100 and DMRDelay to 165. Those settings worked for us, your mileage may vary, but the values should be pretty close. Unlike a hotspot there is no need to touch Rx/Tx Offsets because you already calibrated those earlier in the MTR2000 programming software.
Another factor we haven’t seen mentioned anywhere is temperature control. We noticed our board was running on the warm side when installed in the card cage on the bottom with a wildcard board in the middle and wireline board on the top. The wireline board isn’t needed for our purposes so we pulled it out, moved the wildcare to the bottom slot, and put the STM32-DVM-MTR2K in the middle slot. The increase room for airflow has consistently kept our temp about 8 °C lower then before. If your site has a higher ambient room temp it may be necessary to add a small fan in the top slot of the card cage.
Here are Pi-Stars temp values: < 50°C (122°F) = green; ≥ 50° < 69°C (156.2°F) = orange; ≥ 69°C = red. If you go into the red, expect some CPU throttling. Since moving to the middle card slot our temp is in the ‘orange’ around the 60 °C mark, which is very acceptable.
So far we have tested the repeater in DMR, YSF, and P25 modes, all working great. Our next tasks will include setting up the wildcard board for analog operation and evaluating its long-term stability. Access to most repeater sites is restricted so we want it to be as stable as possible before installation somewhere.
Although we would never use wifi for a site installation to feed internet to it, the Orange Pi Zero does have wifi onboard, but doesn’t appear to have a wifi antenna, its pretty convenient to use wifi at home for testing so we added a small antenna from a busted laptop LCD. It uses an IPEX connector, which is pretty standard in most laptops.
Stay tuned for more…