[Elecraft] OT: Vertical doublets (was: Home made Sigma-GT5 & KRC2 or SGC?)

[Stuart Rohre]

If you use ladderline feed to any antenna vertical or horizontal, you do not
need to match at the center feed point in Theory.  Your Antenna Matching
Unit will tune both the line and the antenna to a match.  You operate a
balanced (ladderline) at high SWR normally, and because of the higher
impedance of such lines and limited dielectric construction of them you
still have very low losses compared to coax feeds (even with SWR line loss).
The Sigma 5 of Force 12 only needs coils at the center feedpoint to match it
to coax without use of a perfect tuner.  IF it were fed with balanced line,
the coils could go away, except for their effect in moving the length toward
resonance on the lowest bands, and easing the job of matching thereby.

Tuners have been widely mesured and have much lower losses in proper
adjustment than many hams believe as has been cited in the work of Witt and
others.  What is rarely mentioned, is losses are related to having several
lossy components rather than fewer.

Typically, capacitors are lower loss than inductors.   Having more inductors
gives somewhat higher loss.  Thus, a tuner with only one capacitor and one
inductor is about the most practical minimum parts count, and this "L
network", has lowest tuner loss over Tees and Pis.   A little studied area
is using the unbalanced L network to load a balanced line without use of a
balun.  It can work.  It would be interesting for someone to do a study on
it.
-Stuart
K5KVH