Still sounds like a low temperature problem. One of the PT's salient
feratures is is very low power consumption, which translates 2 ways:
1. Very long battery life, and
2. Very low local heat generation.
For a balloon payload, #2 can be a disadvangtage, especially if there
is very little thermal insulation between the payload guts and the
forced convection of air down to -80C outside. It is also known that
the VCO free-run freq in the PT xmtr is not temperature-stable; this is
why the PLL tuning procedure is different for balloon payloads. If the
VCO free-run freq drifts too far, the PLL can't pull it in, and the
xmtr goes QRT. Although other balloon groups have had good results
with the PT, EOSS has tested one on 3 flights, and each time, the beacon
failed above about 40K ft in ascent.
Suggest enclosing the PT in at least 1" thick styrofoam with tight
seams, and perhaps even including a chemical glove warmer - one which
carries its own oxidizer rather than depending on ambient PO2. Since
you're using the OT for beacon generation, you might consider adding an
internal temp sensor to one of the telemetry channels, or carrying an
Onset Hobo to log temps in flight.
73 de Mike W5VSI, EOSS
Paulus Adisoemarta wrote:
> According to Mike Manes:
> >Hi Paulus,
> >Kinda sounds like a low-temperature problem. What chemistry batteries
> >were being used? (LiSO2 are the low-temp survivors). Did you run a cold
> >soak test on the modules before first flight? An hour in a beer cooler
> >with a lb or so of dry ice will be worse than worst case.
> >73 de Mike W5VSI, EOSS
> Mike, the battery was Eveready e2 Lithium, and it is rated to -40C,
> so the battery should be Ok.
> The problem was on the radio (PocketTracker), somehow when I reopened
> the package the morning of the flight to reflash the OpenTracker, due
> to a bug in the telemetry firmware, I didn't put back the insulation properly
> such that the Altoids tin can of the PocketTracker touched the inside
> of the mailing tube.
> Thus slowly the radio got colder and finally quit. But when it got
> heated again after touchdown it transmit again.
> The moral of the story, do not work on the payload the morning before
> the flight, as you'll mess up something else.
> Note: the APRS payload is a tandem OpenTracker and PocketTracker together
> where OT is using PT's radio, with different slottime (to prevent
> simultaneous transmission).
> But, we're happy with the performance and persistance of the students,
> they didn't give up even having total loss of downlink.
> Paulus N5SNN
> Yahoo! Groups Links
Mike Manes manes@...
"Things should be made as simple as possible, but not more so." A.