[Elecraft] K3 two antennas without a KAT3-one idea.

[David Giles]

Hello All,

 From time to time the request comes up on how to use the empty second 
antenna port without having to buy a KAT3.  I have a suggestion for 
someone who is able to put the time and effort to devise a hardware 
add-on for the KANT3 board.

Refer to the schematic of the KAT3 ATU.  If you ignore all the tuning 
components (relays K1 to K17 and their 10n capacitors, L1 to L9, C1 to 
C8) what you have left is three shift registers/relay drivers, 2 relays 
(K18,19), a 5volt regulator and a few resistors and decoupling 
capacitors.  There is no microcontroller, its all done with a 24bit 
shift register.

The TPIC6C595Ds could be substituted with 74HC595s and two transistors 
to drive the two relays, though watch out for the different pinouts of 
the chips.

I suppose it could be done as two sub boards attached to the KANT3 - one 
with the shift registers at the mainboard connector end, the other with 
the relays, bleed resistor and spark gap near the antenna connector. 
Best of all, no toroids to wind.

Unfortunately I don't have the time etc. to do this at the moment as I 
am currently prototyping the ultimate accessory for my K3-a new shack to 
house it in.

Any further comments and suggestions welcome.

73 de David VK5DG