[Elecraft] Remote Antenna Tuner

[Jack Brindle]

Let me strengthen Don's comments.

The KAT100 does NOT use the RS-232 signals from the KIO2. It DOES use  
the AuxBus signal. Wayne is very rightfully concerned about RF  
incursion onto this signal caused by long cable lengths or the use of  
unshielded cable. The KRC2 is the only K2 peripheral that uses an  
9-conductor cable to connect to the KIO2/KPA100. We ship a 2-foot  
length of shielded 8-conductor (plus shield) with the kit. I commonly  
use a 9-conductor shielded straight-through cable with my K2/KRC2, but  
then I have extensively tested it, and do not have the KPA option.  
Using such a cable with other peripherals could be very hazardous to  
your station.

There are other things to be concerned with here. A specific example is  
the ALC signal. During testing of the KRC2, it was discovered that the  
loading the KRC2's A/D inputs placed on the ALC signal caused the K2 to  
fail. The KRC2 has a 20K voltage divider to ground on its A/D input.  
This 20K of resistance connected to the K2 ALC input caused the K2's  
output to drop to zero in SSB mode, and caused other strange operating  
situations in CW. We have a warning in the KRC2 manual to leave out the  
KRC2 jumper which connects to the K2 ALC signal to avoid this problem.  
Placing just about any load on the line will cause the problem, no  
matter the source.

Even worse, placing 12 volts (as allowed in the RS-232 spec) on pin 8  
(one of RS-232's RTS/CTS pair) will cause a chip to blow in the KPA,  
and may cause destruction of the microcontroller in the K2. If the  
signal goes to -12V, that 'may' will certainly change to a 'WILL'.

So, to amplify Don's comments, DON'T CONNECT RS-232 TO ANY PINS ON THE  
KIO2 CONNECTOR with the exception of RxD, TxD and signal ground.

By the way, Don - be careful of what you wish. You really don't want to  
see the AuxBus spec, even though you may think you do. Implementing it  
without screwing up K2 operation isn't very easy at all, and puts  
severe restrictions on what else you can do in your microcontroller.

On Sunday, September 7, 2003, at 03:18  PM, Don Wilhelm wrote:

> Fran and all,
>
> WARNING - do not connect RS-232 signals to pins 6, 7, 8 and 9 of the  
> KIO2
> connector!
>
> I know the connector looks like an RS-232 serial port, but it is NOT  
> (Don't
> connect a regular RS-232 cable to the KIO2 either - it will kill the  
> K2).
> The only pins that conform to RS232 are TXD and RXD, chassis ground and
> signal ground - pins 1, 2, 3 and 5.  The other signals are analog  
> (VRFDET)
> or CMOS level digital  (AUXBUS).
>
> I assume that there may be timing issues quite apart from the drive
> capability.  I am not certain what timing assumptions Wayne made with  
> the
> KAT100 design.  The signal timing constraints must be addressed before  
> I can
> even think about how to extend the signal drive distance - the signal
> propogation delay is the problem, not the drive capability.
>
> Gee Wayne, how about some KAT100 timing AUXBUS information for us.  I  
> know
> you want to keep the actual AUXBUS signalling proprietary to Elecraft,  
> but
> what are the timing constraints for communication with the tuner -
> publishing those timings does not have to expose the entire AUXBUS.
>
> 73,
> Don W3FPR

- Jack Brindle, WA4FIB
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