AlexPeterson
Well Known Member
On the trip to Denver this past weekend, I had the autopilot on the whole way. It is a Century 2000, with altitude hold. When the air was smooth, I noticed that periodically the airplane would pitch up and down slightly, about like hitting very light chop. The period was perhaps 1/2 second slight nose up, then back to normal. When we got to some really smooth air, I further noticed that is was always when the second hand happened to be a :43. Hmmm. Turned the autopilot off, and back on. Again every minute at :43. Put the autopilot in attitude mode, no excursions. Put the A/P back in altitude hold, back at :43 again. Turned the aprs off, and no more motion. Turned it back on and off a few times, and nailed the culprit. It seems that the baro sensor in the A/P is getting a little coupling with the aprs output.
My transmitter and (Howell) antenna are in the wingtip, so the stray RF is going a ways. I'm sure Century never had to test our ham frequencies to certify their unit.
Interesting side note - the aprs must transmit at a specific gps clock position all the time, because, even when I removed power from the aprs and restarted it at arbitrary times, it would settle back into :43 after its initial power up transmission. When I compared the analog clock on the panel (from which the :43 came) to the Garmin's gps time, :43 correlated to something like :20 on gps time.
My transmitter and (Howell) antenna are in the wingtip, so the stray RF is going a ways. I'm sure Century never had to test our ham frequencies to certify their unit.
Interesting side note - the aprs must transmit at a specific gps clock position all the time, because, even when I removed power from the aprs and restarted it at arbitrary times, it would settle back into :43 after its initial power up transmission. When I compared the analog clock on the panel (from which the :43 came) to the Garmin's gps time, :43 correlated to something like :20 on gps time.