W9YT Digital Repeater Configuration

The W9YT 443.600 repeater in Madison Wisconsin features DMR and C4FM/Yaesu System Fusion (YSF) functionality in addition to conventional FM voice and Echolink.

output 443.600
input 448.600
FM PL 123.0Hz

Status: http://brandmeister.network/?page=repeater&id=310173

The repeater is the same Kenwood TKR-850 hardware with echolink interface that has been in operation for quite a few years. A SP8NTH MMDVM interface with an Arduino Due connected to a junk-pile PC installed with Ubuntu 18LTS provides an interface to the Brandmeister DMR network.


Early in 2018 another ham on campus introduced me to the TYT MD-380 handheld DMR radio. Priced well under $100 for a very sturdy radio and ability to connect to a couple of local DMR-capable repeaters. The availability of 3rd-party firmware increased the tinker factor and I was hooked.

Next step, could W9YT/BARS support DMR functionality? I did some research and purchased some SP8NTH MMDVM boards from Oshpark and having a fairly well-stocked SMD parts inventory, populated the boards, finished up with a small order to DigiKey and attached the finished boards to a pair of Arduino Due boards. One was ugly-wired to the TKR-850 I have at home -- it works!

Months pass.

With several factors coming into play I made a concerted effort to finish intergrating this board with the W9YT repeater. My first effort involved packaging a Raspberry Pi with Pi-Star firmware all in a nice 1U enclosure. Also compiled and started to configure SVXlink to serve as a repeater controller and echolink interface. Compared to any modern x86 hardware a Pi is quite slow and the PiStar image is small so there were some tweaks to make this happen but it eventually finishes. My test repeater can ID and I figure I'm close!

Another month passes.

The damn Raspberry Pi doesn't boot. It did last month, doesn't now. I've been a linux admin for over a decade and trust me I understand the need to shut these things down cleanly. It just doesn't get past the rainbow boot screen. I think PiStar is a very nice package, but I just don't find the Pi platform attractive for a remote install. I've had too many flash (both genuine Kingston and SanDisk) failures and corruptions on existing Pi installs -- for me, it's not suitable for remote service, even if I have easy access to the location.

As an alternative I built MMDVMHost on an existing reliable x86_64 Ubuntu 18LTS host at W9YT and focused on packaging up the other MMDVM board for use at W9YT along with the existing Echolink interface.

This still leaves a problem of having the repeater service conventional FM voice (let alone Echolink!) along with DMR. Fortunately W5ZIT published some information on how to program a TKR-850 to work on both DMR and FM. Some additional email conversation lead to his revised programming that doesn't require anything special hardware-wise and uses a technique with the TKR's multi-table to repeat and add PL to voice and not repeat a DMR signal. With an example of his programming configuration it was a simple matter to configure for the proper frequency, call, and a few other parameters and get one step close to done.

Echolink. Echolink needs to use the accessory RA and TA pins but also needs PL superimposed because you're going to want PL decode on your radio or you'll be listening to digital modulation at times. As the repeater won't be generating PL in this mode, I need to do it myself. Because it's not 1980, there are no old comm-spec PL encoders handy and I didn't want to pay more for a simple PL encoder than I have so far for the entire project so I looked for alternatives. I found a few examples using a PIC 16F88, 16F84 and 16F678. I tried all three with junkbox parts -- none worked. *shrug* Found another written by PA3GUO using an arduino and LPF that also had a few other features. This also provides some additional functionality. The PTT line from Echolink goes to the Arduino PL encoder which triggers PL generation AND sends another pin low to be diode OR'ed on the repeater PTT. Github copy of PA3GUO code with my modifications.

To provide some operation hierarchy, when the repeater is receiving PL tone, it also triggers output pin 25 which creates a holdoff on the DMR interface. That way analog FM and Echolink operation take priority over DMR. My thought is this is prefereable as an FM-only user probaly can't monitor DMR, but a DMR user can likely decode both modes with the same radio if their QSO is accidentally interrupted. In any case, someone has to go first.

Rough schematic diagram of the W9YT DMR / Echolink interface

innards of the interface

The interface is housed in an old printer switchbox I had lying around. It sits underneath the Echolink interface. Connectors are DE25 and connections between assemblies are via terminal strip with labels on the bottom. It might look like a rat's nest but have you ever looked at the bottom of a tube rig chassis? This one is easy enough to test, modify and change as necessary. Blob on the bottom right is the Arduino Nano CTCSS encoder in clear heat-shrink.

In the future YSF could potentially be turned on but I only know of one other YSF-capable radio in the area (mine) and found those talkgroups dead when compared with DMR. Maybe if a YSF-capable radio could drop below $100...

Tweaks and maybe a sample codeplug for the Madison area to follow.

Tue Jan 22 23:46:56 CST 2019

C4FM/YSF enabled.

This page last modified Tue Jan 22 23:46:56 CST 2019 by timc!

back to my page of electronic tinkering