Some friends and I recently placed a Kenwood TH-D72 on the summit of Saddle Mountain in Oregon, USA, and set it up as a temporary digipeater for use with APRS.

Digipeater on Mountain

The TH-D72 successfully digipeated packets, but when our hiker summited the mountain again the next day, he found that TH-D72 was stuck on the startup splash screen and was unresponsive to any button presses (other than powering off).

I haven’t been able to find any reports of a TH-D72 freezing on the startup splash screen. Does anyone have experience with this? What is a likely cause of this behavior? We haven't seen the TH-D72 freeze on the splash screen before or since.

The sequence of events is roughly as follows:

2017-08-25 15:10:33   -   Hiker sets up TH-D72 and manually sends first APRS beacon.
2017-08-25 16:30:00   -   Hiker descends mountain and leaves TH-72 on summit.
2017-08-25 19:15:44   -   First vehicle comes in range and TH-D72 digipeats an APRS position packet.
2017-08-26 05:09:17   -   Final digipeated APRS packet (all vehicles may have gone out of range at this point).
2017-08-26 06:54:40   -   Final automatic APRS beacon sent from TH-D72 (it seems to have sent beacons up to 00:30:00 apart).
2017-08-26 07:45:40   -   Hiker summits mountain again and finds TH-D72 stuck on the startup splash screen.

The radio was powered by YUASA NP7-12 12V,7.0h battery and 12V to 7.5V switching regulator. The battery manufacturer recommends keeping the battery between –15°C and +50°C for charging and discharging. The temperature on the summit was likely between 4°C and 32°C. The enclosure was vented with a fan.

Two days after the hiker retrieved the enclosure with the radio and battery, we started up the TH-D72 and it successfully sent several APRS beacons. It did not freeze up. The voltage droop during packet transmission was minimal: enter image description here

  • $\begingroup$ Things can freeze for all kinds of reasons, but the standard solution to this sort of thing is a watchdog timer. $\endgroup$ Aug 30, 2017 at 20:00
  • $\begingroup$ @Phil Frost - Any implementation ideas? I might be able to detect the lack of operation with a photo diode taped on the red transmit LED and turn off the radio. But how would I turn on the TH-D72? I believe you need to press a button the front. $\endgroup$
    – watkipet
    Aug 31, 2017 at 18:30
  • $\begingroup$ Possibly unrelated, but have you checked/properly configured the automatic power-off setting? That wouldn't explain the freezing, but it could be causing the radio to shut off in the first place. $\endgroup$ Sep 1, 2017 at 15:18
  • $\begingroup$ Battery: Automatic Power-off and Save were both turned off. $\endgroup$
    – watkipet
    Sep 1, 2017 at 17:08

1 Answer 1


I assume you have extensively bench tested the kit and have not found any problems.

Having several years of experience with high altitude radios in the Alps, I would suspect that you are getting static build-up on the antenna that is glitching the radio.

A Polyphasor, or equivalent, to ground can mitigate static build up. Failing that, a couple of megohms of non-inductive resistance across the antenna terminals may help. I have had success with the resistors in an N connector, plugged into a Tee connector at the radio.

  • $\begingroup$ "Polyphasor" is a brand name for a surge arrestor, right? I assume any RF surge arrestor would work. You mentioned, "Polyphasor... ...to ground." The arrestor I've seen has a terminal for the equipment, one for the antenna, and a mounting hole on the bracket. I assume you mean, "ground the bracket"? $\endgroup$
    – watkipet
    Sep 6, 2017 at 17:58
  • $\begingroup$ Yes, we did extensively bench test it (and in stationary vehicles). Saddle Mountain is only 3,287′, but it's the tallest point the general area. The box and antenna were mechanically, but not electrically, attached to a galvanized steel railing. $\endgroup$
    – watkipet
    Sep 6, 2017 at 18:04
  • $\begingroup$ @watkipet Yes, Polyphaser is a brand name. Connect its ground connection to an earth ground. $\endgroup$
    – Glenn W9IQ
    Sep 7, 2017 at 4:28
  • $\begingroup$ While I can't positively confirm that this is the answer, I'm going to mark it as such since it seems the most plausible. Thanks! $\endgroup$
    – watkipet
    Sep 7, 2017 at 4:53

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