[Elecraft] Remote KAT500

[Jim Brown]

On Wed,12/30/2015 12:20 PM, Rick WA6NHC wrote:
> BUT it should be done with a fully compliant serial device, using the 
> full RS-232 voltages (+/- 12V, some laptops 'cheat' using lower or not 
> negative voltages) in order to extend that far.  Beyond 100' I would 
> expect that the bit rate would have to come down too, but I haven't 
> tested that.  I would also suggest a full 9 wire PLUS shield cable, 
> bonding the shield at both ends to the device/computer chassis via the 
> connector housing.  You may need some ferrite too, to be determined. 

I suggest a different solution for the wiring. Use a decent grade of 
CAT5/6 cable, using one pair per circuit. CAT5/6 is four twisted pairs, 
which inherently reject noise, and it has low capacitance between 
conductors. To avoid Pin One Problems, tie all four "striped" conductors 
together and wire them both to the signal ground pin and to the 
connector shell on both ends. If you do use shielded CAT5/6, wire the 
shields to the connector shells and the four striped conductors to the 
ground pin.

Years ago, we used RS232 to control sophisticated audio signal 
processing systems in theaters, stadiums, and churches. The RS232 cable 
was often 200 ft or longer, running to a laptop. These links worked 
fine. I don't recall what baud rates we used.

As to bandwidth -- RS232 is an un-matched protocol, with a low-Z source 
and high Z receiver, so bandwidth/baud rate is limited by cable 
capacitance. That's why the spec was revised many years ago to reflect 
the availability of low capacitance cables.

73, Jim K9YC