Paul Butzi |||

Minimal Winlink VHF RMS Station

Since sometime in 2019 I’ve run a VHF Winlink RMS that serves the Seattle Eastside/Snoqualmie Valley area. Originally I had a VHF station and a UHF station.

The UHF one ran on a Windows laptop running the Winlink RMS software, and used a Kenwood TM-V71A radio and a TNC-X terminal node controller to do the packet work.

The VHF station was running on a Raspberry Pi, running linux, I tried several different linux based RMS packages, and it was using a Kenwood TM-D710G - a radio with capabilities vastly in excess of need. The problem with running linux is that there is no VARA support on Linux - VARA both FM and HF are strictly Windows. Beyond the VARA problem, the Winlink Development Team are prone to introducing sudden changes that force the developers of linux RMS equivalents to scramble to adapt to those changes.

In the end, the superiority of VHF propagation for this sort of duty became clear, and when I wanted to simplify the whole setup, I abandoned the UHF stuff and put together a more dedicated setup that freed up the laptop and both Kenwood radios, which have been reallocated to more suitable uses.

The simplified station consists of:

  • a little puck mini-pc running Windows 10.
  • a VGA monitor scavenged from the pile of old monitors
  • a Alinco DR-135T mk III radio
  • a Masters Communications DRA-50 sound card
  • Soundmodem packet software
  • licensed VARA FM software
  • Winlink RMS software
  • a Samlex SEC-1235BBM 12VDC power supply with battery backup
  • a group U1 AGM lead acid battery for backup
  • dedicated use of the 2m feed for one of my UHF/VHF antennas.

The mini-pc is one of these. It has a fan for cooling, and after two years of continuous duty, the fan is getting noisy. I’m torn between replacing the fan and just replacing the entire mini-pc with a fanless version.

It turns out the PC for a Winlink RMS can be extremely minimal - very little compute power is needed even if you’re running a software TNC like VARA FM or Soundmodem (or the equivalent Direwolf setup) where all the audio processing is happening on the PC. So what you’re really looking for is a minimal Windows machine, with minimal power consumption and no moving parts to break (no HDD, no fan). Ideally you’d pick one that runs on 12VDC as well so you can roll the entire station onto the 12VDC power solution of your preference.

The Alinco DR-135T mk III radio is just about perfect for this sort of duty. The radio itself is a good performer, bulletproof construction, has no bells or whistles that might complicate setup, and is pretty cheap to boot. For a while they were unobtainable due to supply chain issues but they appear to be available again at the major online sources, and they’re a common swap meet item. The major feature I really like about this model radio is that there’s a TNC interface on the back of the radio that gives you access to the appropriate signals including direct discriminator output and audio input without the pre-emphasis stuff inline, as well as carrier detect and PTT.

The Samlex SEC-1223BBM power supply is overkill, and a much smaller power supply could be used - I just happened to have this PS on hand. Ideally battery backup would be done using a LiFePO4 battery instead of lead acid AGM but so far powergate solutions for LiFePO4 batteries are limited to the wonderful but expensive West Mountain Epic Pwrgate.

This setup has proven solidly reliable. Downtime has been due to:

  • the ethernet switch in my equipment rack died
  • downtime on my internet service
  • various problems introduced by automatic updates of the Windows operating system.

Of the downtime sources, the auto-updates of Windows are responsible for probably 99% of the downtime.

Windows is just not the operating system for this sort of dedicated embedded use, and the auto-update thing is the main reason but only one of many.
Among other problems, it’s hard to make Windows run headless, and if ever there was a situation where you wanted the system to run headless, this is it.

I have not really been following progress on various non-Windows solutions, although I’m aware progress is being made. The problem is that Winlink is very much a Windows only thing - a near fatal defect in my opinion, but there it is.

So, anyway, toward a little approximate accounting of what this all costs:

item approx cost new
mini-pc running Windows $150
monitor $50
Alinco DR-135T mk III $175
Masters Communications sound card $30-$100
VARA license (not strictly needed) $70
12VDC power supply ~$100
total if buying new ~$500-$650

There are other incidental costs like cables, etc. that are ignored in that accounting. Considerable savings could be had by buying used. I should probably add the cost of an antenna and feedline but most hams probably will freeload the RMS station on some existing antenna, the way I do, and in any case feedline and antenna prices vary wildly depending on installation and antenna needs for the site.

But that at least gives some idea of the rough costs for people who are considering setting up an RMS station.

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