[Elecraft] K3 dual receive without KRX3!

[Dave G4AON]

Being an impatient cheapskate, I decided to try running my K3 with an 
external receiver rather than wait for a KRX3... It is very easy to 
parallel the K3 with another receiver, in my case with a K2. While 
perhaps the KRX3 2nd receiver is a slicker option for contest ops, the 
ease with which a K2 can be linked to a K3 is worth a try as most have 
the bits already, including in many cases a K2 that is now gathering dust.

The requirements are to have the KXV3 interface in the K3 and the K160RX 
160m option (for it's receive only antenna socket) in the K2. The only 
other item needed is a receive antenna splitter and that can be made in 
a matter of minutes using a couple of FT50-43 cores and a small project 
box. The circuit at: http://www.qrp.pops.net/swl-ant-split.asp works 
well enough at the lower frequencies, the suggested reduction in turns 
helps on the higher HF bands. On the original windings mine gives 3.5 dB 
loss on 80m and 40m and 32 dB receiver port to receiver port isolation.

The hook up is fairly straightforward, connect the KXV3 RF antenna out 
to the splitter input, connect one of the splitter outputs to the KXV3 
input the other output goes to the K2 receive only antenna socket. Using 
a phono to 3.5mm stereo jack plug lead (centre of phono to tip of jack 
plug), wire the K3 KEY OUT to the Morse key input of the K2.

Transceiver settings:

K3, select external antenna (RX ANT) on the front panel to route the 
receive antenna via the external splitter.
K2, turn power to minimum, terminate the TX antenna socket in a  load 
(any load will do as there will be 100mW at most from it). Turn the 
sidetone to zero, external receive antenna on, key input hand, inhibit 
TX by going into test mode, set TX/RX delay to about 0.5 seconds.

The K2 will go into transmit whenever the K3 is transmitting, so 
effectively it is muted. You have completely independent receivers with 
only a small loss through the coupler, if that is an excessive loss on a 
weak signal you can bypass the external splitter by pressing the K3 RX 
ANT switch. I tend to leave the K2 on 3560 (QRP calling channel) and 
tune around on the K3. By having 3560 CW available via memory recall, I 
can bring the K3 back to 3560 in one press of the M>V button, or if I 
want to work a station elsewhere on the band I can mute the K2 by 
pressing the K3 RX ANT switch.

Note, if you use the KRX3 it too uses a splitter, so you would have a 
small loss in receive performance whenever the 2nd receiver is in use. 3 
dB loss is not a big issue in most cases.

73 Dave, G4AON
K3/100 #80, K2 #1892