Re: [OT] K9YC's Serial Cable question

Posted by Jim Brown-10 on Jun 07, 2011; 10:13pm
URL: http://elecraft.85.s1.nabble.com/OT-K9YC-s-Serial-Cable-question-tp6450273p6451611.html

On 6/7/2011 2:30 PM, Don Wilhelm wrote:
>   sense that only a few are
> willing to replace those computers or USB to serial adapters that are
> classified by Jim's definition of "bad equipment" with good alternatives
> (BTW, I agree with Jim on the "bad equipment".  Many DO need a signal
> return connection to pin 5 or they will not work.

All should understand that Don and I are friends and have the greatest
respect for each other's experience and advice.  FWIW, I've never seen a
COMPUTER or ham rig with a DB9 that doesn't have a conductive shell.  
The very nice Quatech PCMCIA 2-port serial adapters also have conductive
shells that are properly bonded. I have one that I've used on many Field
Days and other fixed and portable operations since 2003, and  I recently
bought two more.  I have no doubt that there are cheap USB adapters
floating around, but because good stuff is also cheap, it's better to
toss the junk and avoid the problems.

Remember also that a shield that isn't connected to circuit reference or
to the shielding enclosure of the equipment doesn't work as a shield.  
Cables that are short as a fraction of a wavelength (1/20 wavelength or
so) can have the shield bonded at only one end if it's not also carrying
the signal return. This is often done with balanced audio cables as a
band-aid for pin 1 problems.  A 3-6 ft cable between computer and rig
bonded at only one end is likely to be just fine below 10M.

Another point that I hope isn't lost on folks -- improper bonding and
shielding causes RF noise to ESCAPE from equipment and radiate into our
receivers, just as it allows RF to get INTO equipment and cause
lockups.  Yet another reason that I'm so bitchy about this stuff. :)

73, Jim K9YC
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