[Elecraft] K2 Band Data

[jerry]

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