Of course there is considerable feedline RF -- the feedline is acting as
a counterpoise, carrying return current from the antenna.
The problem is that the AX-1 is intended for use hand-portable rigs like
the KX3 running battery power CW/SSB. Your attempted use of it as a
fixed antenna and with an attached computer is an un-natural act. :)
The solution to your problem has multiple components. First, add wires
to the coax shield at the antenna to act as a counterpoise. Second, add
a SERIOUS common mode choke at the feedpoint to keep RF off the coax.
http://k9yc.com/2018Cookbook.pdf
Third, carefully bond together the chassis of every piece of equipment
in the shack that is interconnected.
http://k9yc.com/GroundingAndAudio.pdf
An even better solution is to use one or more antenna better suited to
your setup. A quarter-wave wire connected to the center conductor and
another connected to the shield makes a fine antenna; if your K3 has the
tuner, an antenna cut for 30M will work on 20 and 40; one cut for 20
will work on 30 and 17. A choke is needed at the feedpoint (where those
two wires are connected).
All the wiring in your station acts as a receiving antenna for the
equipment, so when your transmitting antenna is close to that wiring, it
WILL act as a receiving antenna and dump it into your equipment. The
solution to that is 1) bonding, as noted above AND 2) ferrite chokes on
that wiring in you station. For those chokes, follow the recommendations
on pages 9-10 of this applications note.
http://k9yc.com/KillingReceiveNoise.pdf
Finally, if you don't already own them, buy a copy of the ARRL Handbook
and the ARRL Antenna Book and study the relevant sections on antennas.
Both are updated every 2-4 years, but the changes are a small fraction
of the content, so a used copy is plenty good enough. Ask around your
local ham club -- it's very likely you'll find a ham willing to sell one.
73, Jim K9YC
On 12/6/2019 12:27 PM, Steve Hull wrote:
I wonder what would happen if you moved the 1:1 choke to the other end of
your feedline (closer to your K3)?
-Steve
On Fri, Dec 6, 2019, 11:41 AM Jobst Vandrey <[email protected]> wrote:
I have been trying to come up with a antenna for use in an apartment with
only limited success. I have now set up the Elecraft AX-1 antenna and it
seems to play well with my K3 indoors with the antenna placed in a window
supported by a folding camera tripod.
One caveat is that there seems to be significant feedline RF so a 1:1
isolation transformer near the antenna feed point is an absolute
requirement. Without the transformer, even 1 watt transmissions caused
various nasty computer gremlins when using digital modes.
My apartment no longer needs to be a maze of wires and switches - many
thanks to Elecraft for this excellent product.
Jobst
AC0LP
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