So far, our balloon group has never concentrated on recovery of our radio
payloads. They have been built "light and cheap" and never cost more than
$25 in parts. However, we would like to improve our tracking and recovery
techniques so that we can launch bigger and better payloads in the future.
For this we need a tracking system which can keep us informed of the
balloon's position all through the flight.
Most ham balloon groups use some variety of APRS tracking, with GPS position
information downlinked on VHF or UHF FM. This system works reasonably well,
but it has some shortcomings:
For these reasons I decided to try another tactic: a VOR-based tracking system,
inspired in part by Mike Manes' 1992
VOR experiment.
Although that effort was less than successful, we believe it should be
possible, even simple, to construct a reliable VOR tracking system that
does all the processing on-board and downlinks just radial information.
The only hardware needed besides our usual payload package is a
VHF "nav" receiver, in this case an old Icom A-22 handheld radio. It has
most of the VOR decoding circuitry already, and we just have to convert the
two phase signals to radial angles in the PIC controller.
The VORtex system was flown on HamBONE-02A along
with a GPS-based tracking system. This was to allow cross-checking and
calibration, as well as providing redundant tracking systems. Unfortunately,
something in the flight chain separated at 14,000 feet and the GPS tracker
crashed without a parachute. The VOR tracker flew on but was never recovered.
VORtex outputted raw phase timings, which were converted to
VOR "FROM" radials with this formula:
Radial = (Timing * 1.544 + 175) mod 360
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