[Elecraft] How accurate is the K3 SWR meter

[Jorge Diez - CX6VM]

Hi Ed,

I have also high SWR (up to 3:1) on my K3 on 20 mts when the amp is
operating. IN the Powermaster it show a 1.5:1. When the amplifier is in
Standby the SWR on the K3 was 1.5:1, so something bad when the amplifier is
running.

I need to do another tests, but your email took my attention.

73,
Jorge
CX6VM/CW5W
K3 #4077

-----Mensaje original-----
De: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] En nombre de Edward R. Cole
Enviado el: Martes, 20 de Marzo de 2012 04:16 p.m.
Para: Elecraft at mailman.qth.net
Asunto: Re: [Elecraft] How accurate is the K3 SWR meter

Just a Post Script (or Note) to the discussion:

I was seeing high SWR using my K3 to drive my new 300w HF amplifier, with
amp bypassed and QRO tuner (that follows the amp) switched directly to dummy
load.  This was on 20m.  I have the K3 ANT1 (no internal tuner) connected to
a MFJ tuner and then thru the 150w Mirage 6m amp and then to the HF amp.
DPDT TR relay.  The 6m amp bypasses when powered off.

Well the solution was removing the 6m amp from the path.  Some ham equipment
is not well designed for other frequencies it appears!  MY SWR went from 1.8
to 1.1 with this simple change.  Actual input SWR when driving the HF amp is
about 1.4 but the bypass thru the TR relay shows no impedance issues as the
50-ohm dummy is seen by the K3 with no "bump".

Since I have a MFJ945E tuner follow the K3, I have two SWR indications to
observe and I do often see a difference in indication if the SWR is high.
Once the MFJ tunes out any SWR they agree.  I have to use a tuner on my
triband yagi (very old), but my 80/40m inverted-V is resonant so tuners are
not needed.  HF amp input matches better at lower freq. bands, though the K3
has no trouble at any band with driving the amp.  The Drake MN2000 was added
when I installed the new HF amp since it can run up to 2kW.  It makes sure
the amp sees a good load and also gives me a monitor for the amp output.

Summarizing:  Check every part of your system from K3 to antenna; you may
find some surprises!  Always check coax line by line!


73, Ed - KL7UW, WD2XSH/45
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