Winter Field Day Prep Project - Yaesu FT-897 Headset Interface

Clearly it's been too long since I last blogged--plenty of catch-up posts to publish this winter. But with Winter Field Day around the corner (as in tomorrow), I wanted to get this project wrapped up - a low-cost interface for an electronics store headset into my FT-897. Yes - I can get much better sound (TX and RX) with a Heil headset, and I'm saving up for one. I just happened to have this older headset laying around, and I typically just use it for Webex and Skype, so I figured it'd meet my needs: a quiet way to operate radio, easier on the ears, but at a fraction of the cost.

After some research, I found this article, which included a wiring diagram: http://www.n1gy.com/yaesu-headset-adaptor.html



The diagram is nicely designed, with polarity guides for the 47 uF capacitor. I could have built this for less than $15 if I'd only ordered one of each components, but I realized my "junk box" is a bit inadequate, so I ordered 10 3.5mm stereo components, a mixed box of caps, and a mixed box of resistors. All told, this build cost $30, with a bunch of parts left over.

For ease of construction, rather than using the brown wires (as in the circuit above) to splice in the RX audio, I simply paired a 3' audio extension cable to the 3' CAT5 cable I used for the TX audio and PTT circuits.

Prior to committing the build to solder, I set everything up on a breakout board:

As you can see below, my breakout board is a bit small, so I had to use jumpers from the stereo input over to an adjacent space on the board, then to the resistor and cap, etc.

 It all seemed too easy - the PTT switch simply closes a circuit (green and blue wires below), which puts the 897 into TX mode, and then the audio feeds along the blue-white and green-white cables (with the audio jack grounded to the solid blue wire that's part of the PTT circuit), but it worked when I tested it. The PTT, TX and RX audio worked great.

With the circuit designed and prototyped, I laid it all out on a simple breadboard. I spent a couple days modeling the wiring in my head, in an effort to shrink the size of the board (my original goal was to have something small enough that I could heat shrink "inline" to the cables, but the audio cable makes it a bit too large for that). You can see one challenge I overcame in the photo below: the ground from the 3.5mm stereo connector has to pass under the trace from the cap. I put a small bend in the cap's trace, and passed a jumper made from leftover CAT5 wire underneath it.

With everything wired up and tested, I drilled a few small holes for a couple zip ties, tidied everything up, and tested it out - great audio report from my local repeater.

The next step is to either trim the board to the minimal necessary size and heat shrink it, or create some sort of enclosure. For Winter Field Day, I intend to simply cover the bottom with cardboard to prevent accidental shorting, and to make a ton of contacts.

73 and good DX!