I recently bought a (used) radio controlled airframe and buried deep inside the tail section is an antenna, broken out to some coax, with an SMA connector within the core of the fuselage. There is no mention of this antenna in the manuals, so I assume it was added by the previous owner. I've tried multiple ways to physically see the antenna (removing it, using a flashlight to see through the tail section, taking apart the tail section), but have not succeeded in physically accessing the antenna.
Based on the frequencies used in radio controlled aircraft, my guesses are that it's either
- 433MHZ for a UHF control link
- 1280MHZ for an analog video link
- 2.4GHZ for either control/telemetry or video
- 5.8GHZ for video
Given that I plan to have a 2.4GHZ control link and a 1280MHZ video link, it would be very beneficial to use the antenna built into the aircraft, however I have no information on the antenna or the polarization.
Are there easy ways to figure this out? My only guess is a very controlled situation with equal power transmitters of each frequency and an RSSI meter, rotating to check polarization as well, or a frequency sweep and SWR meter, which at these frequencies is not cheap.
Edit: Would it be reasonable to measure the current consumption of a transmitter of each frequency with a properly matched antenna, and then with this mystery antenna? My concerns are:
- The current draw of the transmitter may not change measurably just due to a mismatched antenna, especially since the transmitters have voltage regulators built in
- Damage to the transmitter with a mismatched antenna (5.8GHz tx transmitting through a 433MHz antenna - works out to about 3.5 wavelength)