For portable and DXpedition use, I wanted to be able to operate PSK31 and RTTY using my FT-897D and a laptop computer. I thought that PSK31 might be the perfect mode for operating with low power from locations with limited antenna options.
I planned to use AFSK RTTY and also audio I/O for PSK operation, so the first order of business was to determine the audio input and output connections on the FT-897D. This was a bit more difficult than expected due the wording in the FT-897D manual. The manual indicated that audio would be available at the DATA 6-pin Mini-DIN jack on the back of the rig. The associated pins, however, were labeled as "DATA IN" and "1200bps DATA OUT", leading me to wonder if they carried carried data or audio. I put the scope on the output to confirm that it was, in fact, audio.
Looking at an audio recording.
The audio output is on Pin 5 (hot) and Pin 2 (Ground) on the DATA jack. And the audio input is on Pin 1 (Hot) and Pin 2 (Ground).
FT-897D audio input/output is on the DATA jack shown.
Next, using my audio generator and scope I determined the typical audio output levels from the FT-897D and the tolerable audio input levels on my laptop.
Measuring desirable audio input levels on the laptop.
It turned out that the FT-897D produced, typically, 100mv peak audio output and the microphone input on the laptop could handle 5 to 10 mv input. Hence, I needed to construct a 20dB audio pad to avoid overloading the audio input of the laptop when driving it with the FT-897D.
I also checked the output level of my laptop and found it compatible, using the built in Windows volume control, with the FT-897D, so no external adjustments were needed in this case.
I built a little custom cable by cutting a commercial 6-pin Mini-Din Male-to-Male cable in half, using one half and adding a 20dB pad and two TRS (stereo) mini phone plugs at the other end to plug into the microphone input and headphone output of the laptop.
To verify that my planned interface would work, I threw a quick "alligator clip breadboard" together. It did work and I actually made a few PSK31 QSO's with the rat's nest shown below!!
The Rat's Nest
Confirming that everything was working, I finished fabricating the final cable shown below. The 20dB pad (a 10K and 1K resistor) are located under the heat-shrink tubing. This isn't the neatest thing, but it works.
With this cable completed, I did a quick recheck on PSK31 and also tried some RTTY operation. As expected, the RTTY worked as well. So now, I can add this cable to my future travel plans, which often include the laptop and FT-897D anyway, and have the capability to operate PSK and RTTY while on travel. The picture below shows the whole setup. This system can cover 160-meters through 432MHz, SSB, CW, AM, FM, PSK31/63, and RTTY!
The complete travel package.
In case you're curious, the little CW paddle on the right is a Bull Dog, Model BD5, that I picked up a Dayton 2005. It's light as a feather, but has a reasonably good feel to it. I wouldn't use it on a major DXpedition, but it's perfect for a short trip where you might only make a handful of CW QSO's. It's a great alternative to carrying my excellent but heavy Bencher paddle on a short trip.
FYI, I use DigiPan 2.0 for PSK and MMTTY for RTTY. In the picture above, DigiPan 2.0 is running and receiving audio from the FT-897D. You can see the cable described on this page plugged into the front of the laptop. For portable operation I also have a small MFJ-902 Travel Tuner (not shown) that can match all sorts of make-shift antennas.
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