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Troubleshooting the KHF-950 System

January 2022

If you are experiencing tuning and/or garbled transmitter problems with your KHF-950 system, you may have some outstanding Service Bulletins that should be installed.

Consider the following:

  1. Is Service Bulletin (SB) 8 installed in the KTR-953 (Receiver Exciter)?
  2. Are SBs 9, 10, 11 and 13 installed in the KAC-952 (Antenna Coupler)? 
  3. What is the distance (> or < 3 feet) between the mounting location of the KAC-952 and the KTR-953?
  4. What type of antenna (shunt or long wire) is being used on your aircraft?


The following is a list and description of relevant SBs:


SB 8: To reduce transmit distortion encountered when the KTR-953 is mounted in a different location (> 3 feet) than the KAC-952. 


SB 9: To improve common mode rejection encountered when the KAC-952 and the KTR-953 are installed in separate locations. 

SB 10: To reduce transmitter distortion when the KAC-952 is mounted more that three feet from the KTR-953. 

SB 11: To prevent the failure of the power amplifier driver and final transistors.

SB 13: Mod 13 improves the tuning reliability of some shunt antennas.


KTR-953 SB 8 must be installed simultaneously as KAC-952 SBs 9 and 10 to achieve proper system operation and prevent possible unit failure. If SB 9 and 10 are not installed on the KAC-952, SB8 may cause damage to the power transistors that can cost in excess of $2400. 

If the SBs are installed in the KAC-952 but not in the KTR-953, the system may not function properly by either not tuning or being intermittent in performance.

We highly recommend you comply with SB 11 due to its description and the increasing cost of the power transistors. 

If you are using a shunt style antenna, Service Bulletin 13 in the KAC-952 should definitely be installed. In our experience the installation of SB 13 will not affect the performance when used with a long wire antenna.