"Caveat Lector" wrote in
:


"Tehrasha Darkon" wrote in message
...
On Thu, 15 Mar 2007 00:08:30 +0000, west wrote:

I know I can go to eham.com but I like the advice on rraa better. I
also know that this question is somewhat subjective, but if you
will, please indulge. :-)
What is flat out the best vertical HF antenna in your opinion and
why? Thanks in advance.

west
AF4GC

SteppIR. Why use a tuner to match your radio to your antenna, when
you can make your antenna match your radio?

--Teh

No Tuner i.e. TransMatch -- The SteppIRT vertical is remotely
adjustable in length, with continuous coverage from 40 meters through
6 meters - and every frequency in between.

A vertical antenna that is precisely adjustable in length while in the
air solves the coverage problem, and in addition has vastly improved
performance over existing fixed length verticals. The ability to tune
the antenna to a specific frequency results in excellent performance
on every band - and this means the entire band, with very low VSWR.
Resonant antennas must be made a specific length to operate optimally
on a given frequency. So, instead of trying to "trick" the antenna
into thinking it is a different length (traps, coils, etc), why not
just change the antenna length? This is what we have done with the new
SteppIR verticals.

This analysis is along the lines of the traditional "resonant antennas
work better" line.

Sure, a marconi antenna that is adjusted to be a physical quarter wave on
the operating frequency has a feedpoint impedance that yields a low VSWR
on the coax, and feedline losses are relatively low, but the equivalent
loss resistance of the ground connection is significant relative to the
radiation resistance. A quarter wave marconi requires an extensive earth
system for good efficiency.

My reading of Cebik's article at http://www.cebik.com/gp/gr.html is that
simple 4 radial installations have 10 ohms or so loss resistance greater
than extensive (128 radial) systems, which themselves aren't zero loss.
The modelled feedpoint R varies from 4 to 18 ohms above the radiation
resistance of a quarter wave over perfect ground, which implies a
feedpoint efficiency of 90% to 66% respectively.

On the other hand, a longer non-resonant radiator (say approaching a half
wave) has higher radiation resistance (relative to the equivalent ground
loss resistance) which more than offsets the loss expected in a matching
network needed to operate the coax at near unity VSWR for low line loss.
Not only might the longer radiator be more efficient, but it well have a
better pattern (eg higher gain at lower angles or radiation).

It isn't clear to me that the Steppir has "vastly improved
performance over existing fixed length verticals" as you put it. With
enough radials, it is about as good as good verticals get, but there are
other good verticals that don't need as extensive a radial system.

Owen