[Elecraft] K3 --- stopped XMIT during SSB QSO

[Jim Brown]

Simon,

The K3 has RF decoupling, but it also has a pin 1 problem. The 
"pin 1 problem" is the design error that connects a cable shield 
to a circuit board signal common rather than to the chassis. RF 
current then wanders around that common, and the IZ drops on 
common inject it into active circuitry at the whim of the PC board 
layout artist. 

Hams are surprisingly ignorant about the immunity of interconnect 
cables. The K2 shipped with a cable that was shielded but 
consisted of parallel wires. I had BAD RFI with it at only 12 
watts out!  We're also lazy -- preferring to run down to Radio 
Shack and buy a pre-made cable than to pull out a soldering iron 
and build a proper one. 

Since I work in pro audio and am an EMC specialist, I knew that 
twisted pair cable provides EXCELLENT immunity to noise and RF 
pickup, FAR more than straight wires inside a shield. I solved the 
problem by replacing the stock control cable with one made from 
ordinary unshielded CAT5 cable. I wired the cable using one pair 
for each signaling circuit used by the K2 and my computer, with 
the return conductor of each pair used as a signal return. That 
is, one pair for pin 2 and return, one pair for pin 3 and return, 
one pair for pin 4 (CW) and return, the fourth pair for pin 7 
(PTT) and return. 

The second part of the solution was solving "the pin 1 problem." I 
did that by making the "return" connection on each end to the DB9 
shell. 

Using that simple UNSHIELDED CAT5 cable I was able to run 1 kW 
into a long wire antenna on 160M and 80M that ended in the shack 
and ran only about 1 meter from that K2 control cable!  

73,

Jim Brown K9YC

--Original Message Text---
From: Simon (HB9DRV)
Date: Thu, 25 Dec 2008 20:07:44 +0100

A FT-2000 user with a big hairy amp and a CAT cable connected got so much RF into the CAT cable 
that he blew the UART in the FT-2000 and the serial port on the PC. This happened when the antenna 
was rotated to point at the shack. 

I wonder whether the CAT port on the radio has RF decoupling? 

Simon Brown, HB9DRV
www.ham-radio-deluxe.com
----- Original Message ----- 
From: tom kenville 


Last evening I had an annoying problem with K3.  It would stop transmitting any signal, even though the 
red xmit light was lit.



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