[Elecraft] [K2] length of control cables between K2 and KAT100/KPA100

[Don Wilhelm]

  John,

The cable between the K2 and the computer uses different pins than the 
cable between the K2 and the externally mounted "twins" - so the 
conditions are different for each.
The 2 RS-232 signals between the K2 and the computer *should* have good 
noise immunity if the receivers are properly designed.  But I know many 
PC based designs take liberty with the switching levels of the RS-232 
standard.  They can get away with that because most PC based serial port 
operations are over relatively short cables.  Industrial RS-232 
applications can drive several hundred feet of cable with no problems 
(using good quality cable) and you will find closer adherence to the 
standard.

If you can possibly use a standard serial port, I would highly recommend 
that, but if you are stuck with a laptop, you will not have any option 
other than to use a USB to serial converter.  Since you may have other 
devices in your ham station that need serial connections, consider an 
Edgeport 4 port (look on auction sites), but if you want an inexpensive 
single port converter, the ones with an FTDI chipset are being 
recommended at the moment.

Between the K2 and KPA100/KAT100, the critical signal is the AUXBUS 
which may have timing issues with longer lengths as well as possible RF 
pickup problems if your antenna is close to the operating position, or 
you have RF-in-the-shack problems.  The 8R, VRFDET and 12CTRL signals 
are not likely to have problems since they are essentially DC signals.

Jim Brown's suggestions regarding the cable to the computer are good, 
and I have not experienced any problems with the other cable, so I 
cannot say just how far you can go with it and still have reliable 
operation.  I do not recall anyone having problems with a 2 foot cable 
between the K2 and the "twins".

73,
Don W3FPR

On 10/21/2010 9:36 AM, John Shadle wrote:
> I'm almost done with the construction of my K2 "twins" (K2,
> KAT100/KPA100) and am about to construct the control cable for the K2
> -->  KAT100/KPA100 -->  PC.
>
> The instructions from the KIO2 state that the length of the cable can
> be up to 15' (the total length included in the kit), but the KAT100
> manual states that it should be 2' (between the K2 and the KAT100).
> The KAT100 instructions also state that "A longer cable can also be
> used, but it will have to be tested to ensure that is is not subject
> to RF interference". Other conflicting information comes from the KIO2
> manual (first page) which states that "RS-232 interfaces are often
> significant sources of RFI" but that "the KIO2's serial interface
> provides an HF crystal oscillator (operating well outside of any ham
> band) to generate the negative driver voltage."
>
> So, which is it? ;-)
>
> I understand that the cable can pick up stray RF (I'm guessing that's
> why the KAT100 instructions state to make the cable as short as
> needed). Are the cables sufficiently shielded, or not? Should I
> consider purchasing other 4 conductor cables to replace the ones in
> these kits?
>
> As I sidenote, if anyone has information about using USB to serial
> converters for K2 rig control, please reply with that as well. I'm
> about to go searching through the archives now on that subject...
>