[Elecraft] amp and coupler questions

[Pete Goudreau]

If anyone has any comments on the use of the Motorola AN-762 amp with 
the K2 while using an LDG AT-11MP as the antenna coupler and low pass 
filter, I'd certainly appreciate any.  I figure running at or below 
100W, the 3rd harmonic should easily be down better than 40dBc 
regardless of the coupler setting.  Could be wrong about that though.

Also not sure if the input Z of the amp is within the bounds of what 
the K2 can drive safely and efficiently without its internal antenna 
tuner.  Being cheap, that would be the best solution for me.  Anyone 
have any information on that?  I've emailed the folks at CCI 
requesting info but haven't heard anything yet.

And I'm thinking that adding opamp buffers, with the appropriate 
scaling and capacitive cable loading isolation, to the forward and 
reverse voltage signals of the Tandem Match and feeding them to the 
AT-11MP by hacking some connectors and cabling into the AT-11MP.  I 
haven't seen a schematic for the AT-11MP yet but am figuring that 
this might improve the tuning and low power level operation of the 
unit over that achieved via the use of its internal bridge and 
detectors.  Any comments on this would be greatly appreciated as well.

To summarize, the chain would be a K2 w/o the KAT2 but with the amp 
keying ckt, feeding a homebrew packaged AN-762, with diode T/R 
switching, itself feeding a Tandem Match directional coupler and then 
on to the input of the AT-11MP along with the two cables carrying the 
forward and reflected voltages from the TM head to the AT.

Seems complicated I guess but it looks that it could be used from 
QRPp up through 140W in a single setup simply by powering off or on 
the PA, respectively.  And the amp and tuner cost, together, aren't 
much more than the proposed cost of the upcoming K2 PA.

Thanks for listening,
Pete, AD5HD