[Elecraft] SWR issue with K3

[Ron D'Eau Claire]

My guess is common-mode current on the feed line from RF picked up from the
loop since the SWR is stable into a dummy load. 

In an rf-rich environment the rig itself becomes part of the antenna, so
everything cannot be exactly the same switching between the KX3 and K3. 

Assuming you don't have a good low-impedance RF path to earth on the K3, you
might take a 16 foot long piece of wire and attach it to the K3 ground post.
That might eliminate the issue but even if it only changes the behavior of
the SWR bridge in the K3 it would indicate stray RF currents are the cause. 

73 Ron AC7AC 

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Mike
Weir
Sent: Monday, November 28, 2016 1:56 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] SWR issue with K3

While on 20m I tuned the MFJ 1788 to the lowest SWR which was 1.2:1. I did
this using the tune button on the K3. I noticed the SWR on the K3 was
bouncing around from 1.2, 1.3, 1.7, 1.4 and so on and never settling on just
one reading. This only happens on 20m and no other band that I tuned on.
Here is some of the trouble shooting I did.

  1.  I have a KX3 and hooked it up to the MFJ 1788 loop antenna and read
the SWR. It showed 1.2:1 and no "bouncing" issues. I did remove the PL259
from the K3 ANT1 port and connected it to the KX3 so the test would include
all that was in line with the K3. In line meaning coax, antenna switch and
MFJ tuner box.

  2.  I opened up the K3 and tightened all screws ( boards, case, SO-239 and
any checked out the seating of coax jumpers in the rig for a secure fit.

  3.  I tried the K3 on a dummy load and all was good.

I am at a loss as to what is going on and am looking for some input? I check
the rig again today on 20m and it's still having SWR bouncing issues. I have
never had this in the past and am looking for feed back on things to check?


Setup information

Radio K3 with antenna tuner (not being used rig is on bypass)

Antenna MFJ 1788 mag loop

Power 5 watts QRP

Coax RG 8X 30 ft

Thanks in advance

Mike VE3WDM

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