WG4S "Fat Wire" Digital Interface.

The Whole Thing

The Ends

The "Fat Spot"

Drawing

The left side, top to bottom: The right side, top to bottom:

Construction notes:

The Shield braid is compressed to make it large enough to fit over the inline components. If you can turn it inside out, you may be able to assemble the interface without a joint. I didn't think of that, and so I slid expanded braid over the completed interface (after shrinkfit, before Mic connector) and soldered the braids together. YMMV.

Not shown for clarity, is shrinkfit tubing over many of the joints. Apply the shrinkfit as you go. I have shrinkfit over the Collector/PTT joint, the base connections, each AF line to cable connection and a big piece over the whole thing - inside AND outside the shield braid.

Circuit notes:

There are no chokes on the plug ends of the interface. They may help, but since I can't detect any stray RF from my laptop, I didn't bother.

My laptop headphone out level is fine to just slam into the K2. A true computer sound card or a different laptop might overdrive the K2. A 10:1 or 100:1 voltage divider would easily fit, but I didn't need to drop the level.

The resistor is 2.2K. The Transistor is a 2222. The Diode is a little glass thingy that had a band on it and was loose in the junk box. I'm sure it has a number, but I "don't ask, don't tell". The Coax is old RG-62. I don't know what other types might have enough give in the braid to allow you to assemble this "Fat Wire", but it sure is easy with the 62. I pulled the center conductor and insulator out using a vise, and pushed in two pair from some Cat 5 laying around. Cat 3 might be easier to push in (fewer twists per inch) but all my Cat 3 is in use on telephones!

To get Audio-Out on pin 5, I soldered a 2" wire to the fifth jumper, offset the jumper to the numbered side of the header pins (away from the FUNC pin), and connected the free end to the top of R36. This AF Out signal level is variable by the AF Gain control, but it doesn't need any amplification to drive my laptop. I find a very comfortable listening level drives the Digipan waterfall to a "just right" shade of blue speckles with yellow stripes. It's still easy to plug/unplug the FP board as long as you remember the jumper! Maybe I should have stolen one of the grounds on P1/J1, but the wire/plug seems safer to me (and no etch cutting).

My laptop drives RTS active when you CLOSE Digipan. DTR stays low with Digipan running or not, so I used that. The circuit will key off of either, but the rig being keyed whenever the software was closed was a problem.

Don't do it!

This Application Note went up 4/2001. Almost immediately someone on the reflector said "That's a lot or work, why don't you put all that junk inside the DB9 shell?" D-oh! I just didn't think of that. That certainly is a better place for the 2222 etc. I figured that suggestion would follow my original post, but (it's now 3/2004) I just found the original reference on the LA3ZA mods page. I was about to suggest he update his page when I realized I'm hosting the note! So, if you do this, put the "fat stuff" in the Shell.

Dan / WG4S / K2 #2456