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Troubleshooting Lack Of Transmission Issues In Hawker 800XP HF System

March 2024

A Hawker 800XP operator experiencing identical squawks with both #1 and #2 HF systems sought Duncan Aviation Component Services assistance due to a lack of transmissions on either system.

To troubleshoot, we turned our attention to the components shared between the #1 and #2 HF systems. Specifically, we focused on the dual KHF-950 HF system with a shunt antenna, highlighting common elements such as the KA 162 Dual External Capacitor (or KA 160 Dual Antenna Adapter for long wire antenna installations) and the HF antenna itself.

The KA 162 Dual External Capacitor connects the antenna to the active antenna coupler. Given that the HF antenna, in this configuration, is essentially part of the vertical stabilizer leading edge, it was crucial to examine the bonding of the antenna. Proper bonding of the antenna, KAC 952 Power Amplifier/Antenna Coupler, and KA 161 External Capacitor or KA 162 Dual Antenna Capacitor is essential for the optimal functioning of the HF system.

There have been many instances where Duncan Aviation Avionics Technicians have resolved HF squawks simply by cleaning corroded bonding connections at the antenna or antenna coupler.

Tuning faults, another common HF system squawk can also be a result of corroded or poorly bonded connections at the antenna or antenna coupler. Bonding at the antenna coupler involves a bonding strap, and the resistance should not exceed 0.003 ohms.

In cases of intermittent faults in your aircraft's HF system, we recommend you conduct a preliminary check for proper bonding at the antenna and antenna coupler. This straightforward step has proven effective in resolving problems, saving both time and costs in the process.