[Elecraft] K2 Band Data

[Joe Subich, W4TV]

> I see that the aux bus cable - for PC connection - is documented.
> Looks like pin 1 is the shell, pin 2 & 3 are the RXD and TXD, and pin
> 5 is the common. And the protocol is async RS-232 4800 baud, 2 stop
> bits.
That part is the standard CAT interface.  There are several MCU based
band decoders that use the Elecraft/Kenwood CAT protocol (either the
AI "auto-information" data or polling) to derive band data.

CAT Protocol documentation is available in the Elecraft web site
download area.

73,

    ... Joe, W4TV

On 9/1/2023 7:42 PM, jerry wrote:
> On 2023-09-01 12:55, Michael Carter wrote:
>> Hi Jerry,
>>
>> There is no simple access to band data in
>> the K2 unless you want to reverse engineer
>> the AUXBUS protocol.
> 
> *** Considering that it's probably a low-speed
> async protocol, that might not be that hard.
> 
>    Depending on how
>> your homebrew amp selects its lowpass
>> filter options, you may be able to pick up
>> the relay control signals for the K2's bandpass
>> and lowpass filter banks and use those
>> to encode a band data word in the format
>> used by Yaesu.
> 
> *** Yeah, I was thinking of doing just that.  Little
> green wires and a pin header.  Then a little board with
> a microprocessor to convert the 1-low-per-band to the
> needed 4-bit word.  Might be able to do it with a diode
> matrix.
> 
>   There is no isolated connector
>> on the K2 Front Panel, Control, or RF boards
>> that makes available those relay control lines,
>> so you would have to tap the traces where
>> those control signals are exposed.
>>
>> Perhaps you can comment more on the
>> homebrew amp design with regard to
>> lowpass filter selection?
> 
> *** Sure.  The amp uses a W6PQL RF deck and LPF.  It has a
> four-inch touch screen and a Teensy 4.1 microprocessor card.  I
> wrote the software.  It's my third recent solid state linear, and
> I burned out my share of devices on the other two.  Didn't want
> to burn out this one - it's a $230 chip soldered to a heat spreader,
> and would be both expensive and a PITA to replace.  So there is no
> bandswitch.  In addition, there is a protection card that turns off the
> power to the RF deck for
> 
> * Excessive drive
> * Excessive drain current
> * Excessive power output
> * Excessive antenna SWR
> * Wrong LPF selected
> 
>     Even with that last, I prefer to have the linear set its band
> from the exciter data.  Belt & suspenders...
> 
>     People have commented that I should find Elecraft's universal adapter.
> My answer to that is - yeah it would be easy, but not much fun.  I have
> plenty of radios
> 
> The band data is a four-bit word.  1 = +5V, 0 = 0V.
> 0000 - illegal.
> 0001 - 160M
> 0010 - 80M
> ...etc.
> 1111 - illegal
> 
> It works flawlessly with my FTDX10.  It also works with my T41-EP homebrew
> transceiver.  The linear doesn't have true TTL
> inputs:  its internal CPU is a 3.3V device, so there is a voltage 
> divider at each
> band data input.
> 
> I see that the aux bus cable - for PC connection - is documented.  Looks 
> like pin 1
> is the shell, pin 2 & 3 are the RXD and TXD, and pin 5 is the common. 
> And the protocol
> is async RS-232 4800 baud, 2 stop bits.  There is also power available ( 
> I assume 12V )
> max 50mA on pin 8.  I think an AtTiny84 would do it - but I'd need to 
> also put in an
> RS-232 converter chip to deal with that pesky negative voltage.
> 
> There's another pin called "AuxBus".  That's probably a more difficult 
> nut to crack.
> 
>                  - Jerry, KF6VB