[Antennas] coaxial balun

[George, W5YR]

Paul, the very practical problem here is that it is virtually impossible to
do much more than estimate what the driving point impedance of any antenna
will be. It depends upon every scrap of detail concerned with construction,
materials, location, height, ground/soil conditions, other objects within
several wavelengths, etc. etc.
The list of affecting agents is almost endless.

So, in real life, we put up antennas and by making measurements or just
plain guessing, we find what feed system works best according to whatever
criteria are important to us.

It is probably an overstatement of fact, but I think that regarding a balun
as a transformer is somewhat confusing and misleading. A balun serves to
connect a balanced source/load to an unbalanced load/source. Any impedance
matching aspects to that connection should best be done elsewhere.

I am unaware of any strictly coax balun that could be constructed that
would assure a match between an arbitrary dipole installation and a coax
feedline. For many applications, it is far simpler to accept small losses
in the feedline due to the antenna/line mismatch and manage the impedance
matching implications in the shack with a "tuner." 

If that is unacceptable, then there are many techniques for matching the
line to the antenna at the antenna, such as gamma, delta and T matches, but
none come to mind that could be described as a "coax balun." In any event,
such methods may be  narrow-banded in their operation, especially on the
lower bands.

Perhaps someone else can make a positive contribution to answering your
question.

72/73, George W5YR - the Yellow Rose of Texas   QRP-L 1373 NETXQRP 6       
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe SOC 262 COG 8  
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
Icom IC-756PRO #02121  Kachina #91900556  IC-765 #02437

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Paul McInnish - K4BET wrote:
> 
> For a dipole (or flat top as some call 'em) that is fed in the center of
> which the impedance is NOT a true 52 ohms... can some one advise the
> construction details of a coaxial balun (a balun made of coaxial cable) to
> get a good match at the feed point and with the entire antenna being fed
> with 52 ohm coax (LMR-400)?