[OZAPRS] Maxon DM-2550 and TinyTrak3

Andrew Rich vk4tec at people.net.au
Mon May 28 19:37:08 EST 2007

I'm turning a TinyTrak3, Maxon DM-2550 and a Garmin GPS-15 into a
transportable APRS tracker. So far my plan is to jam the whole lot, plus
a small gel battery into a small Pelican case.

> Ok sounds like a plan

I've made up a small LM-317 based regulator for the DM-2550, providing
the transceiver with 10V. I also planned on using the carrier detect
output from the DM-2550 to stop the TinyTrak3 from stomping on other

> I would have used the audio out

It's about here I have come across something weird... I'm powering the
TinyTrak3 from the same 10V regulated supply as the DM-2550.

> I would have powered the TinyTrak off the DC before the volt reg.

If I apply power to the regulator (connected to both the DM-2550 and the
the DM-2550 goes into a non-operational state, no transmit, no receive.

> Under volts or earth loop or regulator protecting itself ?

I originally thought it was the fault of the DM-2550 and Garry was happy
to swap it over, but it's the same story with the replacement.

> Suspected as much

I've got a WXtrak/DM-2550 combo in a half built Peet Bros based weather
station which seems to exhibit the same problem, but _only_ after I
connected the CD line of the TinyTrak3 to the DM-2550. Without the CD
line connected, there is no problem.

> I would be cautious of that CD line

If I unplug the DM-2550 and connect it up again, things are OK and will
be as long as the power supply in maintained.

> Until the DM-2550 tx's ?

And here is the weird
part... if I run the combination from a 9.6V NiCd battery pack, I have
no problems.

> Batteries can supply a burst of current - a regulator will shut itself

If I power the TinyTrak3 from a seperate supply (prior to
the regulator circuit for instance), it's OK as well.

> Suspected as much

Has anyone in the list seen this problem with the DM-2550 before?

> No , but here is what I would suggest

1. Hook your voltage regulator and make sure it is well heat sunk, to the
2. Hook the TinyTrak to run off the volts before the volt reg
3. Ditch the CD idea, use the audio out of the DM-2550
4. Measure the volts and current of your system as the DM-2550 is TX'ing.
5. Establish how much juice the DM-2550 is dragging out of your system,
may be hitting thermal protection overload in the LM317.

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