On Sun, 22 Apr 2007 11:39:02 -0600, Dr. Gerald N. Johnson wrote:
>Antenna at 15' I call close. If the feed line is radiating that makes it
>worse and even with a balun at the antenna, if the feed line isn't at
>right angles to the antenna RF will be coupled to the outside of the
>feedline.
At my old QTH in Chicago, I had very limited space for antennas. On 160 and
80 meters, I used a long wire that ended in the shack and ran within 18
inches of the serial cable connecting the computer to the radio it was
controlling. Using the techniques in my tutorial, I was able to load my
Titan 425 into it at full power. With conventional untwisted serial cables,
the computer locked up with only about 15 watts.
>Most PC serial ports use a variation on the LM1488 as a driver and it
>will put out a great deal more current at transitions than RS-232 rules
>allow and so will drive much larger capacitance loads.
They may drive it, but the capacitance of the cable may do some damage to
the waveform. But the greater noise immunity of using a good twisted pair
like CAT5, and wiring both ends to fix the "pin 1 problem" also make a major
contribution into making long cables work. I work in pro audio, and for
nearly fifteen years, we've use lots of DSP remotely controlled via RS232.
We regularly use CAT5 over distances of several hundred feet.
73,
Jim Brown K9YC
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