Those among us who do both flying and ham radio have a dilemma: as a pilot we usually own a high grade aviation noise canceling headset that is generally of better quality than most headsets available in the ham radio market (I personally own a David Clark H10-13.4 headset … try to find a passive headset with similar robustness). However, all standards regarding plugs etc. are different and it looks like there is no commercial solution available to interface your aviation type headset with your ham radio gear – at least to the best of my knowledge.
So, in the best tradition of ham spirit, I decided to build an interface. Since I still use my headset for flying cutting off the plugs and replacing them with ham plugs wasn’t an option. First problem: where do you find the correct female connector? The phone part of a civil fixed wing aviation headset (caution: different standards for military, helicopter, and commercial airliner!) uses the standard 6,3mm headphone plug equivalent to your stereo headphone. The microphone, however, uses a 5,6 mm three pole plug. No chance to get them at your local electronics dealer. Fortunately there are a couple of aviation specialty mail oder stores than can help you out … for instance Friebe, Siebert, Büscher in Germany, or Aircraft Spruce in the US).
Plugs for the FT-897 are simple. Headphone plug is a standard 6,3mm phone jack (you can actually plug the Aviation Headset right in if you want to), the mic jack is a standard RJ-45 jack. Since I didn’t want to buy the necessary crimping equipment I just used a surplus network cable.
The interface is built in a small box containing the receiving sockets for the aviation headset, the cables to be connected to the transceiver (phone and mic, both ca. 1,5m long), a push-to-talk switch (PTT), and a jack to connect an additional external PTT switch. This way the interface box is very conveniently located in the middle between the headset and the transceiver which gives you additional room to move and enables you to overate the PTT switch holding the interface box in your hand. The following picture shows the overall configuration.
The circuit itself is simple and requires only a few standard parts to provide the microphone with the necessary power and to adjust the microphone output level.
Pin 3 provides via the 470 Ohm resistor the necessary power for the mic, the two 47uF capacitors remove the dc component for the audio input to pin 5. The 1k poti / 6k8 Ohm combination allows for the necessary output level adjustment. A 1nF capacitor removes any HF components that might end up in the system. I decided to include the pin 3 (tip connector) of the headset mic plug that is used in aviation systems as PTT switch. That enables me to use other aviation mics (e.g., handheld mics) with the same interface. Since the aviation standard does not provide a different ground for PTT and MIC I had to connect pins 4 and 7 at the Yaesu Mic connector.
As you see, all components fit comfortably in a 100x50x25 mm box.
Before closing the box adjust the microphone output level using the built in ALC meter in the FT-897. Fine tuning can be accomplished with the “SSB Mic Gain” menu in the FT-897 settings (menu no. 81).
My experiences with the configuration are extremely positive so far. My David Clark headset provides excellent noise cancellation abilities and the noise suppressing microphone works very nicely with my Yaesu rig.
Any further comments and tips are highly welcome.
Vy 73 de Jens, DJ2UM