[Elecraft] K2: Controlling an external amp and tuner

[Don Wilhelm]

  Owen,

The easiest solution to band data outputs for the K2 is to add the KRC2 
- it is a very versatile box and will do what you are seeking and more.

Some hardware added to the BAND+/BAND- buttons on the K2 may be 
possible, but be careful, the buttons are scanned as a matrix by the K2 
MCU, so it may take more than just hard-wiring to the button contacts to 
accomplish that feat, and you would have to assure that whatever you 
added would not impact the band changing operation on the K2 itself.  
Besides, it can get out of sync by using Direct Frequency Entry, so the 
most reliable is to use the KRC2 outputs.

To key your amplifier, I would suggest you look at the AMP KEYING 
Circuit on the Elecraft website (the board is now supplied by Tom 
Hammond N0SS - look also on his website www.n0ss.net).  If you have the 
KPA100, it has an amp keying circuit built-in.  My problem with the RF 
sensed switch is that it is a sure "recipe" for hot switching the 
amplifier - by the time RF is present at the input, the output of the 
amp should already have been connected to the antenna IMHO.

Without the KAT2 (or KAT100) installed, the TUNE button will provide a 
steady carrier that you can use to tune a manual tuner or trigger the RF 
sensing in an "auto-tuner".  That is what it does.  With the KPA100 
installed, the action is the same, but the power is limited to 20 watts.

If your amp produces less than 150 watts, you might consider the KAT100 
instead of your present tuner.  Switch the amp out of the circuit during 
a TUNE and the KAT100 will match the antenna to a 50 ohm input - then 
switch in the amplifier and operate.  The KAT100 has a wide matching range.

73,
Don W3FPR

On 9/24/2010 6:12 PM, Owen B. Mehegan wrote:
> I'm nearing the completion of my K2 (#6991); I finished phase 2 of the
> RF board this week, completed the alignment, and last night I was able
> to hear some CW on 40m with just 10' of speaker wire as an antenna.
> Hopefully I've have it completely done in the next 1-2 weeks.
>
> I'm already thinking about some possible improvements. I have an
> external tuner and an external amp. I built an RF sense switch for the
> amp which will key it when I'm transmitting, but I still have to
> manually change bands on it. This was fine for my first rig, a 40m-only
> QRP transceiver. But it would be cool if each time I used the Band +
> and Band - buttons on the K2, it changed the band setting on the amp.
> The amp has an input for this, I would just need to build something
> that can trigger it. The question is, how would I trigger this from the
> K2? What's the best way to capture the band change events? Use the
> serial interface? Hard-wire something to the band change buttons?
>
> The tuner might be simpler or might not be. Is there any way I can use
> the Tune button on the front panel to control an external tuner?
>
>