P1: Nitrous at Balls in '08

Avionics and Recovery Project

Last Update:

Altitude Measurement and Deployment

Currently, I'm thinking of using a commercial altimeter.



Our current (pre-BALLS) beacon uses a Radiometrix TX2-433-40-5V and RX2-433-40-5V transmitter and receiver, sold by Lemos International (for $24 and $40, respectively, in May 2006).

The transmitter is 10mW at 433.92MHz. We used a hand-made yagi antenna for the receiver.

Radiometrix offers a 100mW version, tunable from 458.5-459.1MHz or 433.05-434.79MHz, the TX2M-458-5/RX2M-458-5 and X2M-433-5/RX2M-433-5. The Lumos International price on these was about $130 and $185, in quantities under 10.


While at HSC, I picked up a pair of Aerocomm transceivers for $65 each: AC4424-200-01 (also with a user manual). These are 200mW 2.4GHz frequency hopping spread spectrum radios with a 2 mile range. These are listed on Mouser's catalog page 6.

More exciting is Aerocomm's 900MHz offering (AC4790), with 200mW rated to 4 miles, and 1W rated to 20 miles. These are listed on Mouser's catalog page 5. These are under $100 with an antenna.


Sparkfun Electronics offers SHENZHEN HAC TELECOM TECHNOLOGY's HAC-LN96, a 915MHz 500mW FSK-modulated transceiver rated to 1.5km for $90.


We have been using the Garmin GPS 18 LVC, available from Provantage for $66 (2007) to $73 (2005). These units have a built-in antenna inside a plastic case with mounted magnets. If you pop the case open, and remove the plastic and the magnets, the actual GPS unit is fairly small. (The OEM version has PPS output.) Specs report velocity accurate to 1000 knots (515 meters/s) below 60k feet (18000 meters).

The GPS 15 does not have an antenna, but lists for under $45 and may be a smaller and lighter-weight solution (10 grams).

GPS Notes

Unconfirmed claims on the net are that operational limits for GPS units are restricted by law to:

  • Acceleration: < 4g (39.2m/s^2)
  • Motional Jerk: < 20m/s^3
  • Altitude: 60000 feet (18000m)
  • Velocity: 1000 knots (515m/s)

Unfortunately, no one seems to know what happens if you exceeed a limit, or if the units continue to function after exceeding a limit and then returning to a state that is below all of the limits. Apparently, either the altitude or the velocity limit may be exceeded -- just not both simultaneously. Of course, how any one manufacturer meets these requirements could vary. The Garmin manual implies that, at high altitude, the velocity will not be accurate, but doesn't discuss the possibility of the unit disabling itself.