Antenna Testing


If the LH Series Little L-PerRegister.jpg (2200 bytes)  or LA Series Aircraft DF receiver seems insensitive or the needle does not point in the DF mode, the problem could be either in the receiver or the antenna system.

The aircraft antenna system can be checked by replacing the LA Series receiver with another LA Series unit from an aircraft with the same system voltage (12 or 28V). Or it can be replaced with a Little L-PerRegister.jpg (2200 bytes)  portable DF (either old style LH Series or new LL Series). Use an extension coax cable if needed. With the aircraft parked on an open ramp, take a practice ELT (or other transmitter) and about 100 feet in front of and to one side of the aircraft. Turn the DF receiver Sensitivity to minimum, turn on the transmitter, advance the Sensitivity control until you hear the signal. (Not needed if using the LL Series L-PerRegister.jpg (2200 bytes)) . The DF needle should deflect to the side pointing to the ELT. Walk the ELT to the other side of the aircraft and the DF needle should follow the transmitter. If it does not, the fault is with the antenna and the antenna coax must be replaced (see 101029 and 101029-3 on the price list). If the replacement DF works properly, the problem is with the receiver.

If the Little L-PerRegister.jpg (2200 bytes)  DF does not point properly, the same procedure outlined above can be used for it. Replace the receiver with one known to be good (LH or LL Series). Use a practice ELT or other transmitter to check the DF performance. If the replacement DF does not work properly, the problem is with the antenna (or mast cable/connectors). If the replacement DF works properly, the problem is with the receiver.

To perform an electrical check of any L-TronicsRegister.jpg (2200 bytes)  antenna except the built-in antennas on the LL series, use either an analog (meter type) ohmmeter on Rx10 or Rx100, or a digital ohmmeter on its diode check range. Most digital meters will not give useful results on their resistance (ohms) scales. On hand held antennas, open the antenna to its operating position while checking.  Disconnect the DF antenna cable from the receiver and measure from the center pin to the shell of the BNC plug on the cable. The reading should not be either shorted or open. Note the value. Then reverse the ohmmeter leads and measure again. The two readings should be equal to within 10% for a good antenna. On hand held antennas, also visually check for broken wires or corrosion at the antenna rod pivots. Portable and magnetic antennas can be repaired by returning them to the factory.

The built in antennas on the LL series equipment are all at DC ground.  Use any multimeter on ohms or diode check range.  Measure from the outside shell of either BNC jack to each of the antenna blades.  Each reading should be less than 10 ohms.   If any resistance is higher, measure to the head of the screw holding the blade on.   If this reading is less than 10 ohms, put a small amount of electronic contact cleaner (not oil or WD-40) in the antenna hinge, open and close the antenna several times and recheck.  If the measurement to the screw head is more than 10 ohms, call the factory.

LAA Series aircraft antenna harnesses are not repairable. Replacement  cable assembies are available from the factory in two versions.  P/N 101029 is for new installations and has a 10 ft cable to run to the receiver.  P/N 101029-3 is for replacement use and has an in-line BNC connector at the switchbox so the cable run to receiver does not need to be changed.

Replacement mast cables are also available (101025 on the price list). If you do a field replacement, use only RG-58A/U or RG58C/U (best) coaxial cable and either crimp or clamp BNC connectors.  (See the connector assembly diagram on the Antenna installation pages). Do NOT use twist-on or set screw versions or RG-59 cable.  They are known not to be reliable.

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