Steve Bonine posted on Wed, 26 Sep 2007 10:12:27 EDT

xpyttl wrote:
Random length, of course, is random. you COULD get lucky. Or not ....

I guess I'm lucky. I've never had a problem matching a random-length
dipole on any frequency I've tried. That does not imply, of course,
that any random length can be successfully used on any arbitrary frequency.

And of course, "random length" should have read "as long as possible,
given the placement of the trees."

Thanks to everyone who chimed in on using an external balum and an
automatic tuner. My gut told me that the consensus ("it won't work")
was correct, but it was nice to get some more factual backup for that.

Steve, the factual backup on antenna matching has abounded
in texts, mostly the 'pro' kind, for years. It's been used for years
to impedance-match all kinds of things within a radio box...as well
as outside it. As to amateur equipment, the subject gets colored
(and both glamorized and defamed) by the lack of comparisons
to other matching equipment and the affinity that some have for
certain brands from certain manufacturers.

If you wish, I can send you a copy of the L-section matching math
that I've previously sent to Mike Coslo in e-mail. It isn't "formal"
but it is accurate, but it does involve simple algebra. The L-
sections are used in most of the automatic antenna tuners
because it is simple (and therefore low-cost) and adapts to the
measure-and-change L- or C- component algorithms that fit into
small microprocessor programs.

The heart of all of them is the Bruene RF voltage and current
detector that senses the phases of each at the load end. [or
variations on that 1955-beginning detector] The micro then
determines which parts of the L- or C-components are to be
switched in or out to get close to the ideal in-phase E & I of
RF for most power transfer.

Now the designer-manufacturers don't make auto-tuners that
will match ANYTHING...even though it CAN be done. To reduce
manufacturing costs they limit the number of internal inductors
and capacitors and THAT will reduce the ability to auto-match
anything. They are trying to be competitive on price. The newer
transceivers have SOME internal auto-tuning capability but they
clearly state the limits of their equipment. Not all separate auto-
tuners specify that. [I have both just as a backup]

"Baluns" aren't all perfect, either. They are good but just not
perfect. Some are better than others but it would take ALL of
them and some good lab test equipment to do a good
comparison. However, MOST work well enough for amateur
radio purposes and do allow for balanced-to-unbalanced line
conversion at HF.

Now ANY impedance-matching tuner will let one load up just
about anything. All that serves is to transfer the most RF power
into a load. What is NOT known is WHERE all that RF is going.
Unless some ham has a balloon-borne sensor and data transfer
gizmo, NOBODY can know just where the pattern is going to be.
Big trees WILL affect the pattern, especially changing it between
dry and wet climate times and between different kinds of trees.
So will structures and assorted conductive things (aluminum
patio covers, small garden sheds, power, phone, and TV cables)
all within the near-field (within five or so wavelengths). Even
some houses which have had aluminum siding added on
compared to similar houses with just wood or stucco or brick
siding.

One can take an example of the U.S. Army's little AN/PRC-104
backpack transceiver. It covers the whole of HF using a whip
antenna. It has had an auto-tuner built-in since it went
operational in 1986. A human bean is a poor counterpoise for
any antenna with HF wavelengths and soldiers aren't all "built
to spec" for that purpose. Further, the transceiver and whip must
operate from unknown field environments, in trees or well away
from them, in swampy soil or dry desert. The transceiver can't
get any higher than the soldier carrying it. But, the little built-
in antenna tuner assures him that the whip antenna is going to
get as much RF power into/out-of it as possible. The rest of it
is trying to keep the whip as vertical as possible while in-use.

Now a PRC-104 won't win any DX awards or enable contacts
with Antarctica or Yurp, but it is a case-in-point where an auto-
tuner certainly helps maximize signals in a 1:10 frequency
range with a practical-minimal fixed antenna, allowing for a
highly-variaable counterpoise/ground-plane environment. The
vertical whip will probably maximize its pattern between 10
and 40 degrees above horizontal, give-or-take. It works in
practice (for the equivalent of QRP amateur-style). Works
well enough, that is. The auto-tuner built-in certainly helps
it.

Everyone's residential location varies greatly and only a very
few are "perfect" (as to the antenna analyzer programs). One
can load up practically anything with a tuner but only the shape
and arrangement of conductive elements is going to determine
where most of the RF goes to (or comes from). No tuner can
help that.

73, Len AF6AY

"AF6AY" wrote

Lots of good stuff snipped....

Now ANY impedance-matching tuner will let one load up just
about anything. All that serves is to transfer the most RF power
into a load. What is NOT known is WHERE all that RF is going.
Unless some ham has a balloon-borne sensor and data transfer
gizmo, NOBODY can know just where the pattern is going to be.
Big trees WILL affect the pattern, especially changing it between
dry and wet climate times and between different kinds of trees.
So will structures and assorted conductive things (aluminum
patio covers, small garden sheds, power, phone, and TV cables)
all within the near-field (within five or so wavelengths). Even
some houses which have had aluminum siding added on
compared to similar houses with just wood or stucco or brick
siding.


Everyone's residential location varies greatly and only a very
few are "perfect" (as to the antenna analyzer programs). One
can load up practically anything with a tuner but only the shape
and arrangement of conductive elements is going to determine
where most of the RF goes to (or comes from). No tuner can
help that.

I had to leave the important stuff... sorry to make everyone scroll down....
Len, I'm confused as to just what you're specifically referring to. Do you
mean a doublet fed with balanced line (300 or 450 ohm window line) to a
transmatch in the shack is something you don't recommend? Or are you
referring to this system fed with coax to an autotuner? It'd seem to me
that, as long as the system (fed with window line to keep the serious losses
down to negligible) is in the clear, the transmission line is 90 degrees to
the doublet for the "required" distance... all should be fine and the
radiation pattern should emanate properly from the antenna itself, not so
much the transmission line. ?

Howard N7SO

On Sep 26, 3:46?pm, "Howard Lester" wrote:
"AF6AY" wrote

Lots of good stuff snipped....

Now ANY impedance-matching tuner will let one load up just
about anything. All that serves is to transfer the most RF power
into a load. What is NOT known is WHERE all that RF is going.
Unless some ham has a balloon-borne sensor and data transfer
gizmo, NOBODY can know just where the pattern is going to be.
Big trees WILL affect the pattern, especially changing it between
dry and wet climate times and between different kinds of trees.
So will structures and assorted conductive things (aluminum
patio covers, small garden sheds, power, phone, and TV cables)
all within the near-field (within five or so wavelengths). Even
some houses which have had aluminum siding added on
compared to similar houses with just wood or stucco or brick
siding.
Everyone's residential location varies greatly and only a very
few are "perfect" (as to the antenna analyzer programs). One
can load up practically anything with a tuner but only the shape
and arrangement of conductive elements is going to determine
where most of the RF goes to (or comes from). No tuner can
help that.

I had to leave the important stuff... sorry to make everyone scroll down....
Len, I'm confused as to just what you're specifically referring to. Do you
mean a doublet fed with balanced line (300 or 450 ohm window line) to a
transmatch in the shack is something you don't recommend? Or are you
referring to this system fed with coax to an autotuner? It'd seem to me
that, as long as the system (fed with window line to keep the serious losses
down to negligible) is in the clear, the transmission line is 90 degrees to
the doublet for the "required" distance... all should be fine and the
radiation pattern should emanate properly from the antenna itself, not so
much the transmission line. ?

I'm trying to point out that any good tuner can "load up" to
ANYTHING...i.e., transfer RF power out of the transmitter
and into whatever the "load" is. If the "load" is just a
transmission line, a very lonnnnng one, the tuner will "load
up" on that. If the "load" is your favorite antenna type, it
will "load up" on that.

Once the RF power has been transferred into this load,
then it is up to the conductors in the "load" to radiate it
into whichever direction you expect it will go. But, do NOT
expect ANY antenna to behave properly (for radiation) if
its near field is impugned by nearby dielectric material
or conductors.

Mostly I was making a comment on "loading up" phrases
which I consider an incomplete description of what is
really happening. A tuner, any tuner, will do the job of
transferring RF into the "load." That isn't the whole story.
Next is what the "load" does with it to create the EM
wavefront. No tuner can help that.

If you are satisfied with your particular method of getting
RF out of the transmitter and into some antenna, fine.
Satisfaction is all part of the game. Such satisfaction is
not the example to set for all. It seems to me that every-
one's location is different and each presents a unique
problem to solve for the more-optimum EM wavefront
launch direction in that location.

Anyone who says that one kind of antenna is the "best"
or one should "always" use a certain kind of balanced
transmission line isn't looking at the whole picture. They
are probably describing just the only (or a few) antenna
installations they used. Yes, some antennas "work
better" than others. In a particular location.

For someone just starting out, I would suggest just a
vertical for HF. It is the least obtrusive to neighbors (can
be described as a "flagpole") and most will perform
adequately (to launch an EM wavefront) with a few radials
for the "ground." No, it won't win awards or work DX
"better" than Brand Y using Brand T transmission line,
but it WILL radiate adquately...and that's the whole name
of the game, ain't it? :-)

73, Len AF6AY

On Sep 27, 2:27?pm, AF6AY wrote:

If you are satisfied with your particular method of getting
RF out of the transmitter and into some antenna, fine.
Satisfaction is all part of the game. Such satisfaction is
not the example to set for all. It seems to me that every-
one's location is different and each presents a unique
problem to solve for the more-optimum EM wavefront
launch direction in that location.

Anyone who says that one kind of antenna is the "best"
or one should "always" use a certain kind of balanced
transmission line isn't looking at the whole picture. They
are probably describing just the only (or a few) antenna
installations they used. Yes, some antennas "work
better" than others. In a particular location.

All that is certainly true. But I don't see anyone
saying that one kind of antenna is "best" for all locations,
or that one should "always" use a certain kind of transmission
line in all applications.

It's also not the whole story, either, because what
must also be considered is the sort of radio operation
that is being considered. Does the ham want only DX,
or regional/national QSOs? Several bands, or only one
or two? Will operation be confined to one part of a band,
or spread out over the entire band?
What time of day will most operating take place?
Will there be ragchewing, net operations, contesting?

All that and more have an effect on what the 'best'
antenna is for a given location.

For someone just starting out, I would suggest just a
vertical for HF.

Depending on a whole bunch of factors, that could be
good advice, or very bad advice.

It is the least obtrusive to neighbors

Not always. It depends on the location. A wire
antenna can be much less noticeable than an
HF vertical in many situations.

(can
be described as a "flagpole")

Perhaps, but I don't think anyone who has
seen a typical manufactured amateur HF
trap vertical would consider "flagpole" an
accurate description.

and most will perform
adequately (to launch an EM wavefront) with a few radials
for the "ground."

Maybe - and maybe not.

The performance of an HF vertical is dependent on
many factors, such as the ground system, objects
in the near field, how much loading is used to obtain
resonance, ground losses in the Fresnel zone, etc.

No, it won't win awards or work DX
"better" than Brand Y using Brand T transmission line,
but it WILL radiate adquately...and that's the whole name
of the game, ain't it? :-)

It may not radiate adequately.

For example, on the lower HF bands such as 80/75 and 40 meters,
the dimensions of a full-size quarter-wave vertical and radials may
become impractical (60+ feet on 80/75, 30+ feet on 40 meters).
Most trap vertical designs use a considerable amount of
inductive loading on those bands, reducing the efficiency and
radiation resistance as well as the SWR bandwidth.

The lack of high-angle radiation from such a vertical may make it
almost useless for daytime and closer-than-DX-but-farther-than-local
communication on those bands. An amateur located in a valley, such as
the one who started this thread, might prefer
useful radiation that leaves the antenna at angles that would leave
the valley.

At this point in the sunspot cycle, the amateur bands above 11 MHz are
often useless for ionospheric propagation much of the time,
particularly during darkness hours. Having an effective antenna for
the lower HF bands can be the difference between making QSOs
and not making them.

There's also the cost factor.

Yes, "everyone's location is different and each presents a unique
problem to solve". Which means that recommending a vertical
antenna to someone just starting out could be very bad advice unless a
lot more information was gathered first.

And if Brand Y using Brand T transmission line works better,
why not use it?

IMHO, the "whole name of the game" is useful radio
communication. IOW, making QSOs.

I have seen situations where it was good advice to tell a ham starting
out on HF to put up a vertical. I have also seen situations where that
would be very bad advice. Same for dipoles of various kinds,
loops, random wires, etc.

73 de Jim, N2EY

wrote:
On Sep 27, 2:27?pm, AF6AY wrote:


There's also the cost factor.

Yes, "everyone's location is different and each presents a unique
problem to solve". Which means that recommending a vertical
antenna to someone just starting out could be very bad advice unless a
lot more information was gathered first.

And if Brand Y using Brand T transmission line works better,
why not use it?

IMHO, the "whole name of the game" is useful radio
communication. IOW, making QSOs.

I have seen situations where it was good advice to tell a ham starting
out on HF to put up a vertical. I have also seen situations where that
would be very bad advice. Same for dipoles of various kinds,
loops, random wires, etc.


The main reason that I recommend a dipole over a vertical is that it is
general purpose, and just doesn't take as long to put up and get going.

My first dipole was up and running in a day. Then I put up my vertical
while I could operate. The vertical took a lot longer to install. I had
to pour the concrete base, and running the ground wires was the sort of
project that I put them in as long as my back could stand it, until I
came up with my trenching method. The tuning of the antenna required
several putitup takeitdowns. and 75 meters was very touchy - it still is
too sharp tuning to take in the whole voice or CW sections. THe results
are that I had two nice antennas, but the vertical is more of a
specialized instrument, one that I switch to or from depending mostly on
how far away the other Op is - but even then, conditions will change and
one or the other antenna will operate better than the other at different
times.

My experiments with both have allowed me to definitively state that
between the dipole and the ground mounted vertical, the best performer
is yes.

- 73 de Mike KB3EIA -