[AMPS] Where to read Reflected Power

[Jim Reid]

Hi,

Was tuning up for some CW on 10 meters today.  Decided
to also use my linear,  Henry Ultra.  This amp comes with
a Bird coupler on the back of the RF deck.  However,  I
have a 4' length of RG213 on the output connector from the
deck which runs to a low pass filter,  then another 3 ' of
RF 213 runs back up to the Bird coupler assembly on the
back of the deck.  From the Bird,  I run another 10 feet or so
to a Hofi rotary switch which allows me to switch an MFJ-
259B to the antenna to adjust the antenna tuner for good
match.  On my antenna tuner is another "cross needle"
meter.

What I noticed is that when I have the antenna tuner set for
almost perfect match using the 259,  then switch to the
rig set up,  I read reflected power at the Bird coupler on the
back of the RF deck,  but none on the antenna tuner meter.  Or,
I can adjust the antenna tuner so that there is no reflected
RF power read on the back of the RF deck after the LPF,
but read around 50 watts reflected now at the antenna tuner
meter?

This is on 10 meters,  and I also found that I could not get the
antenna tuner to match to my C4 beam until I had added a
3' length of 213 to the feedline coax coming from the antenna
to the back of the tuner!  This tells me that on 10 meters one
is liable to read about anything anywhere in the set up when the
antenna does not match the feed system exactly.  I have no
idea what the impedance up at the antenna actually is,  but
with the 259B switched in,  and the tuner bypassed,  the 
MFJ unit says the impedance is R=22, X=19, vswr=2.6.
With the tuner set to read essentially 0 reflected power
on the Bird at the RF deck,  that is with the tuner now in
series with the antenna analyzer,  the analyzer reads
R=45, X=24, vswr=1.6,  but  tuner switched to the antenna
now,  there is about 50 watts reflected read on the tuner meter,  
as would be expected with other that R=50,  X=0 or close to 
those numbers.  But,  as I said,  the Bird on the back of the
RF deck is reading essentially zero reflected into the
output of the amplifier terminals.

So,  do I want to set the tuner for minimum to zero reflected
power at the output of the linear,  or zero reflected power on
the back of the antenna tuner,  where,  presumably,  the
antenna tuner meter is reading?

Seems to me,  I want zero or near it,  reflected on the output terminal
of the linear,  right?  And,  as I have not noticed this on
the lower bands,  maybe this is just a 10 meter situation I
have stumbled upon with my set up here.

Will experiment later on the lower bands,  out of time for this
today,  hi.

73,  Jim,  KH7M


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