"Steve Bonine" wrote in message
...

I agree that a random length dipole fed with ladder line makes a great
antenna. I've used one for years with a traditional tuner. My

I would strongly suggest against a random length doublet. A non-resonant
doublet will have impedances all over the place. At some freuencies it
cannot be matched at all, at others the losses in the tuner make you wish
you hadn't been able to tune it. The trick is keeping those nasty spots out
of the ham bands.

There are a number of G5RV type antennas that are doublets whose length has
been chosen to keep those nasty spots out of the ham bands. Spend a few
minutes looking up the right lengths for your doublet and avoid potentially
a lot of grief.

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

...

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 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 -

On Sep 25, 11:03?pm, "xpyttl" wrote:

I would strongly suggest against a random length doublet.
A non-resonant
doublet will have impedances all over the place.

That's true, but it's not a reason to reject the 'random length'
doublet.

Spend a few
minutes looking up the right lengths for your doublet
and avoid potentially
a lot of grief.

It's not just the doublet length that matters but also the length,
impedance and loss of the transmission line. Antennas like the
G5RV choose a combination of dipole and transmission line
length that present reasonable impedances on several bands.

A very useful tool is modeling software such as EZNEC or G4FGQ's
DIPOLE3. They will give useful predictions of shack-end impedance, so
you can judge if it's in matching range or not. So even if the antenna
is 'random' length, you can have a good idea if it will match and how
efficient it will be before you put it up.

With regard to transmatches, also called antenna tuners, for balanced
loads, the two typical amateur approaches are the unbalanced-tuner-
followed-by-a-balun method, and the link-coupled method. The
unbalanced-tuner-with-balun method assumes the balun does its job over
a wide range of impedances, which isn't always a good assumption,
while the link-coupled method can be complex to bandswitch.

A third method, described by AG6K, consists of a balun followed by an
L network - the balun is on the rig side of the transmatch rather than
the antenna side. Thus the balun only has to deal with 50 ohms
nonreactive once the L network is adjusted. Google AG6K to see a
description of his method. Although his tuner uses ganged roller
coils, fixed coils with taps could be used in a homebrew version for
simplicity and lower cost.

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

Modeling software can be a big help in removing the randomness.

73 es GL de Jim, N2EY

wrote:
On Sep 25, 11:03?pm, "xpyttl" wrote:
I would strongly suggest against a random length doublet.
A non-resonant
doublet will have impedances all over the place.

That's true, but it's not a reason to reject the 'random length'
doublet.

There are indeed certain lengths that are best avoided. Certainly you
don't want the doublet to be near 1/4 wavelength in total length on a
band you intend operating on. In the MFJ tuner manuals, there is some
text on lengths you would want to avoid for our purposes.


Spend a few
minutes looking up the right lengths for your doublet
and avoid potentially
a lot of grief.

It's not just the doublet length that matters but also the length,
impedance and loss of the transmission line. Antennas like the
G5RV choose a combination of dipole and transmission line
length that present reasonable impedances on several bands.


Trick antennas such as the G5RV and OCF dipoles utilize some clever
techniques to match impedance. Haven't used a G5RV, but my experience
with the OCF has been fairly satisfactory. I would note that after it
broke, I elected to put up another doublet with ladder line and tuner. I
have been pleased with that.


Modeling software can be a big help in removing the randomness.

Good advice. They are also an excellent method of comparing the
efficiencies of the various antennas. Low VSWR is not always the mojr
indicator of antenna performance.

One of the biggest reasons that I suggest the general purpose doublet is
that the new Op gets an antenna up that doesn't have all of the foibles
of a precise dipole, such as antenna height above ground, interaction
with nearby objects, and can get multi-band operation in the deal.

The new guy or gal can then learn quite a bit by using the tuner to
match up the antenna to the rig, and can see which bands are interesting
to them.

Especially important, I believe is that they won't become confused and
give up. I know when I started in this hobby, I got enough confusing
advice that at one point I almost hung it up because there appeared to
be just no way that I could put up an antenna that would work. The
antennas that I could put up were going to be too low to the ground,
they were going to be too short, and on and on.

Fortunately my Elmer pulled me aside, and said "try this". Within a
week, I had my doublet up and running, and I've worked the world with it.

Now I can cogitate on all the various antennas and their proponents
without keeping myself off the air in the meantime.


- 73 de Mike KB3EIA -

On Sep 27, 10:53?am, Michael Coslo wrote:
wrote:

it's not a reason to reject the 'random length'
doublet.

There are indeed certain lengths that are best avoided.
Certainly you
don't want the doublet to be near 1/4 wavelength in total
length on a
band you intend operating on.

Why not, other than the fact that such a short dipole will present a
feedpoint impedance that has a low resistive part and a high reactive
part?

In the MFJ tuner manuals, there is some
text on lengths you would want to avoid for our purposes.

Never had an MFJ - my transmatches are all homebrew. I've read the MFJ
manuals, and it seems to me that they were trying to avoid
lengths of antenna-plus-feedline that would present very low or very
high impedances at the Transmatch end of the line.

It's not just the doublet length that matters but also the length,
impedance and loss of the transmission line. Antennas like the
G5RV choose a combination of dipole and transmission line
length that present reasonable impedances on several bands.

Trick antennas such as the G5RV and OCF dipoles
utilize some clever
techniques to match impedance.

I don't consider the G5RV and OCF to be 'trick' antennas. They're
simply intelligent combinations of dipole and feed systems that
have been worked out to present reasonable impedances so that
line losses and Transmatch requirements are reasonable.

Haven't used a G5RV, but my experience
with the OCF has been fairly satisfactory. I would note that after it
broke, I elected to put up another doublet with ladder line and
tuner. I have been pleased with that.

In the dipole-category of HF antennas, I've used G5RVs, OCFs, dipoles
fed with ladder line and a Transmatch, coax-fed dipoles, fan dipoles
and coax fed trap dipoles. Plus inverted-V versions of most of those.

In my experience they are all comparable radiators of RF *if* they are
implemented in a way that keeps feedline/transmatch loss low and gets
the antenna up and in the clear. IOW, none of them are magic, and they
all have their applications.

They

[antenna software]

are also an excellent method of comparing the
efficiencies of the various antennas.

Not just the antenna but the feedline system as well.

One of the biggest reasons that I suggest the general purpose
doublet is
that the new Op gets an antenna up that doesn't have all of the
foibles
of a precise dipole, such as antenna height above ground,
interaction
with nearby objects, and can get multi-band operation in the deal.

That's true to a point, but there are other tradeoffs, such as the
absolute need for a Transmatch, the need to avoid certain lengths,
and the difficulty of handling balanced lines in some situations.

IMHO, it is better to have a station that works well on a few bands
than to have one that works poorly on all bands. Many multiband
antennas, such as many commercially-manufactured "all band" HF trap
verticals, are so full of compromises that their performance on some
bands is highly compromised.

Fortunately my Elmer pulled me aside, and said "try this". Within a
week, I had my doublet up and running, and I've worked the world
with it.

That's the ultimate test of any antenna system: what have you worked
with it?

My first HF antenna was an inverted L - what some would call a "random
wire", even though there was nothing random about it.
It was end-fed and worked against a ground/counterpoise system
consisting of the radiator piping and a lone ground rod. I made many
QSOs with it and later versions.

The big problem with HF/MF antennas for the radio amateur is that
the best choice is so dependent on the site and what the amateur
intends to do. This is why it is impossible to give general advice
about HF antenna types that is any good, without knowledge of
the available resources and intended use.

73 de Jim, N2EY