[Elecraft] K3 SO-239 Connectors

[Robert Tellefsen]

Good post, Paul.  Than you.

I've added it to the notes I'm collecting for things
to check when my K3 comes.

73, Bob N6WG

----- Original Message -----
From: "Paul Christensen" <w9ac at arrl.net>
To: <elecraft at mailman.qth.net>
Sent: Saturday, March 15, 2008 7:59 AM
Subject: [Elecraft] K3 SO-239 Connectors


> As indicated earlier, I included a link to a photo that shows my
K3's
> upgraded Amphenol SO-239 connectors.
>
> 216.229.20.37/images/K3.jpg
>
> The Mouser catalog P/N is 523-83-798.  The Amphenol P/N is 83-798.
>
> In spending some time reviewing the placement of the K3's SO-239
connectors,
> the RF connector mounting configuration can be improved with only
minor
> re-work as shown below. In the link to the following photo, you will
see the
> two panel-mounted SO-239 connectors with three (3) solder-lugs added
as well
> as the KAT3 ATU Board.
>
> 216.229.20.37/images/K3-1.jpg
>
> The K3 comes with both the ANT 1 and ANT 2 SO-239 connections routed
to the
> KAT3 board with only a single-ended wire.  The connectors' RF return
path
> necessarily relies upon clean, tight, but unbonded connections
through the
> chassis and also through a path of screws washers, and an aluminum
spacer
> that holds the KAT3 to the K3' side panel.  In the photo, you will
see that
> the final RF attachment point to the KAT3 is through a zinc-plated,
> Phillips-head screw located at the upper left of the board.  This is
the
> same attachment point whether its modified or unmodified.  Only, in
the
> modified layout, bus wire connects the SO-239 connectors straight to
the
> zinc screw connection point.  Removal of the KAT3 board is just as
easy as
> it was before.  It's now also possible to replace the aluminum
spacer with a
> ceramic or fiber spacer which, will force all RF current along the
new buss
> wire and keep high RF current from circulating through the K3's
chassis.
>
> At 100W of RF, I am not completely comfortable with the existing
arrangement
> given my past experiences with transceivers of other manufacturer
who
> similarly use single-ended RF wiring techniques and rely upon good
chassis
> and hardware connections for the RF return path.  In almost all
cases where
> RF ingress was an issue, those cases were resolved by creating a
direct RF
> return path from the antenna connectors, rather than allowing 100%
of the RF
> current to flow and circulate through the chassis.  True, in a
bonded
> configuration like this, the chassis will still allow for some RF
current,
> but the level of chassis RF current can be reduced by either: (i)
running a
> short buss wire from a solder-lug on the SO-239 connectors to the
KAT3; or
> (ii) using short (3") coaxial cable from the SO-239s to the KAT3
with
> shields bonded at both ends.   I suspect that ANT 1/ANT 2 antenna
port
> isolation may be improved by using the coaxial option.
>
> Since the wire length between the KAT3 and SO-239 connectors is so
short, I
> decided to use #20 AWG buss wire with solder-lugs, rather than use
coaxial
> cable, although ideally, something like 2 or 3-inch cuts of RG-174
with
> Teflon dielectric would be ideal.  I may switch to that at a later
point and
> verify port isolation results.
>
> Paul, W9AC
>
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