[Elecraft] K3+P3+Microkeyer II

[Jim Brown]

On Sun,6/18/2017 5:20 PM, Joe Subich, W4TV wrote:
> Using the Icom controls is far more
> reliable than using a "Y" connection on a RS-232 connection; it avoids
> issues with loading RS-232 circuits and the isolated CI-V Transceive
> emulation provided by the microHAM interface avoids issues with
> collisions/corrupted commands on a shared CI-V bus.

I know you know this, but others might not -- RS232 is NOT a matched 
system. It uses a low-Z driver and a high-Z receiver. The real issue 
with loading is CAPACITANCE -- later versions of the RS-232 Standard 
reference cable capacitance and baud rate rather than cable length as 
the limit of transmission distance. CAT5/6/7 cables are among the lowest 
capacitance paired cables we can easily buy, and their loss is fairly 
low at RF. CAT5/6/7 cables are four twisted pairs, each with a different 
twist ratio to minimize crosstalk. RS-232 cables wired to use one of 
these pairs for each of the signalling circuits are about as good as it 
gets without spending big bucks. Most ham gear uses only RXD and TXD 
(pins 2 and 3 on a DB9) with pin 5 as return.

My serial cables use two pairs to connect 2 and 3 with both pairs 
returned pin 5, and with the remaining conductors wired to the DB9 
shells. My cables are pretty short, but I've used cables like this that 
are 200 ft long or longer to connect a computer to sound system DSP to 
do system setups at fairly high baud rates.

73, Jim K9YC