[TowerTalk] Walt Maxwell responds to Steve Best

[Jim Reid]

Steve,  I am still thinking about all of this,  your thesis,
my measurements,  etc.

First thought:

I am still  looking at  the case I measured when not
using the tuner;  just had the amp feeding directly to
the mis-matched terminated feed line.  Recall from
my May 9th post:

"2.  Connect the feedline directly to the Force 12   40 meter
dipole,  without the use of a tuner.  That is,  with the amp
tuned to drive 1000 watts with the given input power, into
a 50 ohm,  pure R,  load,  what will occur when it is
connected directly to the R=17, X=11, vswr=2.9:1 antenna
"system" load?   

NOTE:  [Did remeasure this feedline input Z,
recall I found,  with the MFJ-259B that  R = 17,
X = 11,  vswr = 2.9.]

    Result:  Without touching the amplifier tune or load
controls,  Power forward reading,  using Bird 1000 watt
slug,  was 700 watts;  rotating slug to the reverse,  
reflected power position, 180 watts.  This was done with'
the amp tuned to deliver 1000 watts into the 50 ohm
load;  input drive about 30 to 33 watts.

3.  Realizing that the amp was no longer tuned for
optimum performance at this new,  non-50 ohm  pure
R load,  I "tweaked" the tune and load controls to
peak the forward power reading.  The "tweaked"
control settings were,  tune=348,  load=520.
Bird readings increased to:  power forward = 1400 watts
(using the 2500 watt full scale Bird slug);
power reflected = 360 watts(using 500 watt slug)!  
Or 1400 minus the 360 watts reduces to  1040 watts;
or,  it seems we are back to 1000 watts output from
the linear amp (again allowing for Bird meter/slug
tolerances).  Input drive remained constant,  and assume
the gain of the amplifier did not change when retuning the
Pi-L amp output circuit to match the 17,  j11 load impedance.

Now this is occurring with the output tank circuit of
the amplifier "re-tuned"  to provide a max output
power with given input power to the mismatched-
feedline/antenna "system".

And,  here the amp output power seems to be the
difference between the measured Pf and Pr.

After such an adjustment of the amplifier Pi-L
output network, is the transmission line between
the amp and the mismatched feedpoint at the
antenna "conjugately"  matched?

I have a lot of confidence in the feedline system Z
as measured/reported  being:  17,   j 11,  vswr 2.9.

Second thought:

Recall some of the numbers  you had me collect 
Wednesday,  Steve; they certainly indicate such a
line input Z, see:

One of your requests of the 10th:

These were to be done with the tuner set up to match
the 50 ohm rig system to the 17, j11 load Z.

">  * Jim can you terminate the tuner input with Zo and measure 
> the impedance seen looking rearward into the tuner output.  

Measured at the end of the 18 inch jumper coax again
between tuner output and the meter input connector:

Meter reads:  R = 17,  X = 7,  and vswr =  2.8 "

Bingo!  Isn't  this,  if we new the reactance sign,  probably
the near conjugate of the impedance that this tuner's
output was connected to when the tuner components were
set for a system "match"  at the tuner input??

And,  further,  you asked:

> * Jim - connect a 50 ohm load at the tuner output and 
>  measure the tuner input impedance. [with the tuner
adjusted to a "match" condition between the line and
the rig.]

And,  my report:

"With the Bird 50 ohm dummy load connected at the tuner 
output,  the MFJ meter reads:  R =  18 ohms,  and 
X = 6 ohms,  and vswr = 2.7 "

So,  it appears to me the tuner is providing  the
necessary impedance transformation such that
a conjugate match does exist on the output line
up to the mis-matched feedline-antenna system.

These numbers are just too coincident,  allowing for
slight deltas in reactance but a nearly constant R
value,  for this not to be the case.

As I said,  I am still thinking about all this,  hi.

Third thought:

Also still mulling over Mauri's,  I4JMY,  comment:

"When two REAL sources are paralleled, the impedance 
of the "virtual"  generator obtained is the parallel of the 
two individual impedances at  point were paralleled. 

The developed voltage across the virtual generator is 
actually that  value producing a power equal to P1+P2 
if the load itself (conjugate)  matches the source,.....
(The load impedance is here intended as the resulting 
impedance at the  point were generators are paralleled) 
It's also possible to calculate separately the delivered 
power (and  developed voltage) of each generator across 
the load, but in this case the second generator must be 
present in the circuit for the  calculations and considered 
as another load, with negative impedance, in parallel with 
the first one."

And fourth:

Mathematical manipulative tools are just that,  tools with
which we attempt explanations of what we can actually
observe and measure.  We have some (approximate)
measurements,  and several differing ways of applying
tools for explanation,  hi.

73,  Jim,  KH7M







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