K5RWK’s New UHF Multi-Mode Repeater

By Chip Coker KD4C

Way back in 2021, we had a plan to upgrade our K5RWK UHF Analog repeater and move it to a better location. Well, after COVID and some other extended delays, I can report that it’s now on the air, but still at the old location on top of the old Methodist Hospital at Collins and Campbell.

So what’s changed? The old UHF analog repeater on 443.375MHz has been retired and replaced with a more powerful Motorola MTR2000 running 80 watts (still on 443.375MHz). Thanks to a 2021 Micro-Grant from the Irving ARC, we have a new commercial-grade UHF antenna and a set of new TX-RX Systems UHF duplexers. The repeater has a MMDVM board that allows it to repeat multiple modulation modes (more on this in a bit). The new repeater and duplexers are in a new self-contained environmental enclosure.

Why is it still in the same location? We had intended to move the entire new UHF repeater to the East Renner Water Tower, but we’ve been unable to get the antenna installed on the Water Tower (we’re not allowed to do the installation – must be a city-licensed contractor). Because it’s a low-priority project for the city, and because other things keep happening (like the City Hall fire), we could never get the antenna install scheduled, so the project got stuck for over a year.

Will it get ever get moved? We hope that we will be able to move it to the East Renner Water Tower or some other high location on the east side of town (which was the point for doing the upgrade) at some point. In the mean time, we wanted to get it on the air (and Andrew wanted to reclaim the space in his garage).

Is the performance better in the same location? Yes, the equipment is much better, the transmitter is running a higher power (more than double the old TX power), and the antenna has a significantly better radiation pattern. If you had trouble using the old UHF repeater, this should be significantly better. Also, don’t forget that you also get a performance boost with the digital modes.

What’s up with the Multi-Mode stuff? The new repeater will do Analog FM (like the old one), but it will also repeat DMR and D-STAR and M17 and a couple of other modes. How can it do that? Ultimately the RF portions of the repeater don’t care what the modulation scheme is – it’s all the same at RF. At the heart of the repeater is a MMDVM (MultiMode Digital Voice Modem) that steps in and handles the Digital waveforms. So you can use this repeater with an analog FM radio, a DMR radio, or a D-Star radio. You can only do a single mode at a time (there’s 15 seconds between mode changes), and it’s NOT a cross-mode repeater. FM analog radios can only talk to other FM analog radios, DMR only to DMR, D-Star only to D-Star.

Why not Fusion/WIRES-X also? Because we have a perfectly fine YSF repeater on Palisades (444.725MHz) that is linked to WIRES-X with a much taller antenna and wider range. We don’t need this for Fusion in addition to that one.

DMR and D-Star can be linked to other things. Can we link this new repeater? Yes, D-Star (node K5RWK B) can be linked to external Reflectors just like a normal D-Star repeater. The DMR mode is tied to the Brandmeister network, so you can activate most any Talk Group that’s available on Brandmeister. People paying attention might ask “wait, my hotspot is on Brandmeister. Can I talk to this repeater using my home hotspot?” Yes, if you are connected to the same Talk Group on your hotspot as the repeater is, then you can have a conversation with someone on the repeater (this is completely different than what’s available on our other DMR Repeater at UTD). There’s some specifics on how to make this happen, but it’s very possible.

Why do you have DMR Repeaters tied to two different systems? Basically, there is a place in the world for both. Our DMR repeater at UTD does what it does and does it well. It’s only linked to the most popular Talk Groups on the DMR-MARC system, and that is done to maintain as much “quality” as possible on the system. This new MultiMode repeater with DMR opens up the Brandmeister world to repeater users, but with that comes all the “wild wild west” that entails. Right now, it’s all open, but we reserve the right to ban any problem child TGs in the future.

How do I use it? If you have a radio programmed for the old analog FM repeater, everything should still work as it did previously. If you have a DMR capable radio, program this repeater into a new channel along with your desired BM talkgroups (Texas 3148 is a good one to start with). If you have a D-Star radio, program a K5RWK B channel (it’s probably a bit new to show up in the D-Star directory) and go! Remember, each mode will have to be a separate memory channel in whatever radio you’re using, and I’m not aware of a single radio that will cover all of the modes. If you need detailed help in programming, just ask.