Elecraft OT: Problems with K3 + external PA to specific antenna on 80m

[Kjeld Holm]

Wishing all of you a Happy New Year.

As stated this is off topic but at least the antenna giving me problems is
used with my K3 (and the Expert 1K-FA power amplifier).

Antenna: Sigma 80 + Tornado drive. This is a center fed shortened vertical
dipole with 'top' and 'bottom' loading (horizontal tubes) looking like a H
tilted 90 degrees and with the now vertical part being longer in a normal H.
See
http://www.texasantennas.com/index.php?option=com_content&view=article&id=96
&Itemid=108. The Tornado drive is a moveable remote controlled coil placed
in the center of the dipole. See http://www.seco-systems.net/. The result is
resonance on 40m when the coil is compressed - resonance on different
frequencies on 80m as the coil is expanded.

Setup
K3 with coax to PA (Expert 1K-FA) coax further on to a sensor for
PowerMaster (power/SWR meter) and again coax from this sensor to the antenna
(the latter link is about 20m (60ft).

Problem
PA will not work into the antenna on 80m.
Strange readings at the coax entering the shack: PowerMaster showing SWR 1.4
and Power e.g. 500 W (for about 15 W input). The PA showing about 500 W
output but zero or a very little number of Ampere. This is giving a lot of
RFI in my speakers. Running key down for a few moments does NOT heat the PA
at all. It seems to me that I am getting very few answers on calling
stations.

My conclusion
The PA does actually NOT output 500 W.

Further information
Bypassing the PA it seems to me that my K3 is drawing normal amount of
current for varying levels of output up to the 100 W. It seems to me that I
am getting answers as to be expected on calling stations.

The whole setup seems to be working OK on 40m.

Measurements with antenna analyzer MFJ-259B say
3.5 MHz: SWR=1.4 R=63 X=17
3.6 MHz: SWR=1.4 R=69 X=13
And changing rapidly with change of frequency if the Tornado drive is not
readjusted (this is as expected)

7.087 MHz: SWR=2.5 R=19 X=0
This is a bit high for the SWR but the SWR curve is relatively flat from 7.0
to 7.2 MHz with a dip around 7.020 and never getting over 3.2. Contacts are
rolling in - no complaints.

My hope
That some of you can tell me what is going on - and even better how I can
solve the problem.

Vy 73 de
OZ1CCM "Kel"

PS
I am daily enjoying reading the Elecraft reflector and learning as much as I
can from all those very knowledgeable fellow hams.


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