On Sat, 2 Apr 2005 21:12:35 -0000, Ronald Stuy wrote:
>With CTwin there was no RFI problem at all.
>What could be the problem? Is there some hardware component in the laptop
>that is used by Writelog and not by CTwin?
Can't answer about CTwin, but I had SERIOUS RFI keying my K2/100 from my
IBM laptop with Writelog via the serial port UNTIL I fixed the wiring on
the serial interface. It was a very simple fix, with two components.
1) I replaced the standard K2/100 serial cable (which uses un-twisted,
parallel conductors) with a piece of shielded CAT5 cable. Twisted pair
cable is a VERY powerful cure for RFI, and the more twists per foot, the
better. CAT5 cable has a very high twist ratio.
2) I connected the signal return at each end of the serial cable to the
SHELL of the DB9 connectors, NOT to the so-called signal ground pin. This
keeps the RF out of both the radio and the computer.
At the K2 end of the cable, I route the keying signal to the base of an NPN
transistor that does the inversion and level-shifting to key the K2. The
collector goes to the hot side of the key jack, the emitter to the shell.
Before I changed the cable, I couldn't get above 10 watts with the K2/100.
After the fix, I can use the K2 to drive my TenTec linear to 1 kW. Oh -- by
the way -- the antenna is an end-fed long wire that runs within 2 ft of the
laptop on its way out of my shack. I've also used this same setup on Field
Day, both with a K2/100 and a TS850.
Jim Brown K9YC
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