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

[Gary Peterson]

”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...