[Elecraft] [OT] K9YC's Serial Cable question

[Jim Brown]

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