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

[Ron D'Eau Claire]

Kjeld, that sounds like rf "loose" in the system (or shack), based on your
report that the Powermaster shows absurd readings and the symptoms change
with frequency and power levels. 

The Powermaster uses a microprocessor to calculate SWR and power. Some rf
getting into that logic would produce the weird readings. 

It's likely rf is getting into the power monitoring circuits for the Expert
1K-FA doing the same thing - making it "think" you are putting out lots of
power so it stays throttled down. 

Is there anything "common" to the 1K-FA and Powermaster other than the coax
that might be piping rf into them (other than the coax)? 

It might be rf on the outside of the coax shield leading into the shack. I
don't know what sort of protection the Tornado coupler/drive offers, but you
probably know that RF can flow on the outside of the coax shield
independently of the RF on the inside of the shield. The rf on the outside
can then couple into many things in the shack. 

If you have a separate ground in the shack, you might try connecting it to
the OUTSIDE of a coax connector shell at the Powermaster and see if that at
least changes the behavior (it might fix it). That would confirm it is RF on
the outside the coax causing the problem. Even using the mains safety ground
may show you a difference (although you may not want to keep it connected
because RF is then being fed back into the house wiring). 

Depending upon how far the antenna is from the rig, you might be getting
some direct radiation pickup from the antenna too, either directly into the
house wiring (that then passes it into the shack) or directly into
control/power wiring to the 1K-FA or Powermaster.

Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Kjeld Holm
Sent: Sunday, December 26, 2010 7:26 AM
To: 'Elecraft Reflector'
Subject: [Elecraft] Elecraft OT: Problems with K3 + external PA to specific
antenna on 80m

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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