On Tue, 30 Jun 2009 11:15:50 -0700 (PDT), Julius Fazekas n2wn wrote: >My first attempts were OK, but laced with problems. Often I had to drop from >5 watts to 2 to keep my logging computer from locking up in a key down
The fundamental cause of this problem is the improperly designed serial cable for the K2. It uses parallel wires, and is shielded. A proper cable designed for RF immunity requires TWISTED PAIRS. I ran into exactly the same problem you did in Chicago, when my antenna for 80M and 160M was a long wire that ended in the shack and was fed against a counterpoise. That put a current maxima in the station, right next to the computer, and the associated magnetic field coupled into the serial cable and locked up the computer (in my case, at about 8 watts). The fix was quite simple. I replaced the parallel wire cable between the K2 and the computer with CAT5, using one pair for each signal circuit. I also terminated the return of each pair to the SHELL of the DB9 rather than pin 5, fixing a pin 1 problem that also couples RFI. With that simple fix, I could run my K2 to my Ten Tec Titan at full power with no RFI. The wiring of a conventional serial cable is documented in http://audiosystemsgroup.com/HamInterfacing.pdf Note that the K2 serial cable is NOT a standard serial cable, so the wiring in the applications note applies only the wiring between the K2 and the computer. No change is required for the wiring between the K2 and KPA100. Note also that a cable shield provides NO magnetic shielding, only ELECTRIC shielding. Twisting is required to prevent magnetic coupling, and also greatly reduces electric field coupling. Nearly all coupling in the near field of an antenna is magnetic, except at higher HF frequencies. It would only be necessary to shield this cable if you are using high power above 15MHz with an antenna that is within a few feet of the rig. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
