I cut my teeth using coax and still do for my radio astronomy interests.
However, I use a 450 foot long doublet on 630 through 6 meters with a home
brew L-Network matching network. The feedline is parallel wire /
windowline transmission line. I don't worry much at all about losses in
the feedline or the matching network due to something other than 50 ¡ÀjX at
the input to the matching network. However, it's not a system for the
newbie to amateur radio HF operation.
Dave - W?LEV
On Fri, Sep 18, 2020 at 1:42 PM Jerry Gaffke via groups.io <jgaffke=
[email protected]> wrote:
Dave states:
1) Design the antenna by whatever means one chooses
2) Address the resulting matching as a circuit problem *
Good hard engineering and true to the physics of the problem like
Krauss
and Balinas approach the problem as such, two separate solutions.
That is preferred when building an antenna for a fixed frequency with a
specific radiation pattern.
If building a 4 element yagi for 14.1 mhz, that is exactly what I would do.
And a 50kw broadcast station cannot just put up a random wire and use an
antenna tuner.
But most amateurs do not operate at a fixed frequency, and can tolerate
the often
unnoticeable losses of reflections bouncing between the antenna feedpoint
and antenna tuner.
Way more convenient than having a yard full of antennas for each favorite
operating frequency.
The radiation pattern is pot luck and varies with frequency, but that can
be part of the fun.
As Dave states in this post:
/g/nanovna-users/topic/76222973#16961
an antenna with a perfect match driven through 100 feet of RG8x
at 30 mhz loses 100%-63% = 37% of the power to attenuation in the coax.
As I show in posts 16960 and 16956 of that thread, if you then change
frequency to where
the antenna has a 4:1 SWR, an antenna tuner at the rig (instead of at the
antenna feedpoint)
will lose an extra 16% of the transmitter power due to the reflections in
the lossy coax, on top of
Dave's perfect 37% loss. That 16% is pretty much unnoticeable to the
operator at the far end.
If using ladder line instead of coax, these losses in the transmission
line can be close to zero
even with very high SWR's. This is Walter Maxwell's primary argument
throughout the book,
go ahead and use an antenna tuner at the rig to give the transmitter a
proper match.
If you are concerned about antenna patterns, best to design the antenna
for a specific frequency. But if all you have is a 40 meter dipole (or a
rain gutter),
it's worth using your antenna tuner to see if you can get a match on some
of the other bands.
Jerry, KE7ER
On Thu, Sep 17, 2020 at 02:23 PM, David Eckhardt wrote:
Section 13.3 of the Maxwell tertise states (NOT Clerk Maxwell of the
famous
'4-equations' which tied EM theory together in the late 19th Century!!):
" The antenna tuner really does tune the antenna to resonance, in
spite of opinions to the contrary of those who are unaware of the
principles of conju-gate matching. The tuner obtains a match, by which
all reactances throughout the entire antenna system are
canceled, including that of the non-res-onant antenna, thereby tuning it
to
resonance."
*He addresses the antenna plus 'tuner' as a system. In that respect, yes,
the matching network or transmatch 'tunes' the system such that all the
impedances 'agree' without loss or reflections. HOWEVER, most antenna
engineers would not approach the problem differently, as such. *
*1) Design the antenna by whatever means one chooses
2) Address the resulting matching as a circuit problem *
*Good hard engineering and true to the physics of the problem like Krauss
and Balinas approach the problem as such, two separate solutions. The
"Maxwell" treatise seems to me a bit removed from good hard antenna
theory
(with calculus et. al. the stuff that gives us headaches)! It's more of a
technician's 'cookbook' rather than a solid treatment of the subject.
Neither the Krauss nor Balinas or Jasik (which I do not have and wish I
did!) treatments address the circuitry to establish a match. All rigorous
antenna references (those two are my personal favorites) derive the feed
impedance and leave it there. All antenna engineers I've ever worked
with,
including the Dr. Allen Love who designed some of the first Arecibo
feeds,
approach the problem as the two-step solution, not including any
adjustable
reactive components. These texts treat various methods of establishing a
match at the antenna and as a part of the antenna like the gamma, T, and
transmission line matches, but not the traditional concept of the
'transmatch'. Once the antenna array / radiating structure is designed
and
the feed impedance is established, it's turned over to the circuit
designers. The 'Transmatch' belongs in the purview of the RF engineers /
RF circuit designers.*
*All rigorous RF design engineering texts DEFINE RESONANCE as +jX = -jX,
leaving nothing but pure resistance of the radiating structure (antennas)
or lumped system (resonant and tuned circuits circuits). Personally, I
will ALWAYS side on the side of rigorous treatment of the subject as
taught
in the hard, rigorous engineering and physics texts. *
*Adjustment of various reactive components in NO WAY can alter the
physical
structure of what is considered 'the antenna'!!! ! ! ..... *
*Dave - W?LEV *
--
*Dave - W?LEV*
*Just Let Darwin Work*
