[Boatanchors] Was 813 grid to filament... - now antenna tuners

[Gary Schafer]

Hi other Gary,

To add to your comments:

I think the title of the article you were thinking of from Maxwell was "My
antenna tuner really does tune my antenna".

The conjugate match as offered by Maxwell (Walt) can be misleading to some.
I never did like the way he explained it as he seems to insinuate that the
characteristics on the transmission line are altered in the process, which
of course they are not. 
The same SWR and line loss still exist due to the mismatch of the antenna
and line.

But I agree that whatever is done at the antenna tuner is reflected at the
antenna end of the line.

Looking at what a 1/2 wave length of transmission line looks like at one end
with a mismatch at the other end is a good example of what Maxwell is
talking about. The 1/2 wave length of line gives us the same R and X value
at the transmitter end as what is at the antenna end. Changing the antenna
to alter R or X at the antenna end, the same change is seen again at the
transmitter end. It also happens the other way around.

If the impedance is inductive at the antenna it will also be seen as
inductive at the transmitter end of the line. The antenna tuner must be
tuned to be capacitive in order to obtain a conjugate match. 

Now we can remove the transmission line and place the antenna tuner directly
at the antenna without retuning it! 
With the transmission line in the circuit we have effectively matched the
antenna from the other end of the line!

With a line length of other than a 1/2 wave length the line will transform
the resistive and capacitive values to new values depending on line length
but the same holds true for seeing the tuner R and X (transformed)at the
antenna as well as the antenna R and X (transformed) at the tuner.

The idea is that what happens at one end of the transmission line also
happens at the other end.

It takes some thinking to get your head around the concept.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of Gary Peterson
> Sent: Saturday, October 03, 2015 8:19 AM
> To: boatanchors at mailman.qth.net
> Subject: [Boatanchors] Was 813 grid to filament... - now antenna tuners
> 
> 
> ”You are correct. Actually what they are are (adjustable) impedance
> transformers...
> Eugene W2HX”
> 
> >N0DGNsaid:
> >They are matchboxes!  the impedance of the antenna hasn't changed one
> little bit!
> > All you do is make the transmitter/transceiver happy.  The feed line
> and the antenna don't change one iota.
> 
> It is not incorrect to call the matching device in your ham shack an
> “antenna tuner,” rather than a matchbox, a transmatch or an impedance
> transformer.
> 
> Walter Maxwell, W2DU (SK) wrote on this subject in a series of articles
> in QST, called “Another Look at Reflections.”  He also published at
> least three editions of a book called “Reflections.”
> 
> Mr. Maxwell was no dummy when it came to this subject.  He was an
> antenna design engineer, employed by RCA, and several of his designs
> ended up in Earth orbit and on the Moon.
> 
> Maxwell pointed out the importance of the conjugate matching theorem,
> which states that if a conjugate match is achieved at one point in a
> system, then a conjugate match exists in every other point in the same
> system.
> 
> A conjugate match is defined (paraphrasing on my part) as having equal
> resistances and equal reactances (if there is any), of opposite sign, as
> one looks in both directions from a point in a system.  An example would
> be at the feedpoint of a dipole where, at a given frequency, the
> resistance of the dipole is 82 ohms and the reactance is +j 35 ohms
> (inductive).  Looking back into the feedline, the resistance would be 82
> ohms and the reactance would be –j 35 ohms (capacitive).
> 
> Assuming a low loss feedline, this means that if you achieve a match, in
> the ham shack, with your L, tee, pi or whatever network between your
> transmitter and feedline input, there now exists a conjugate match
> between the end of the feedline and the antenna.  One of his articles
> was entitled “My Transmatch Tunes My Antenna,” as I recall.
> 
> Mr. Maxwell is in good company.  Several of my BSEE and MSEE friends are
> in complete agreement with him.
> 
> There is no reason to jump on anyone who refers to the matching unit in
> their shack as an “antenna tuner.”  It is just one of several correct
> terms for the device.
> 
> Gary, KØCX
> 
> PS -  I just got out of bed...so I hope there are no typos in above...
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