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Old September 27th 07, 12:46 AM posted to rec.radio.amateur.moderated
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"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



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Old September 27th 07, 12:43 PM posted to rec.radio.amateur.moderated
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Default Suggestion for an HF starter rig

I have an ICOM T-90A (it's my first radio). It's a good "klunker" handheld
radio for beginners. There's a lot you can learn with it; you can't break
it unless you intentionally and deliberately try to. Some things are
annoying, like the fact that the battery charge takes 14 hours, unless you
have a special charger, and you can't transmit while the battery is
charging, but all this is safety-oriented, apparently.
-Mindraker


wrote in message
. ..
I am a newly licensed technician, study for the general exam. I plan to
purchase an HF rig soon and would appreciate suggestions on a good starter
rig. I am budgeting $800 for a rig and antenna. I would be happy with a
good used rig but I am not sure where to start looking for information.

Thanks,

Jim KI6ISQ



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Old September 27th 07, 12:43 PM posted to rec.radio.amateur.moderated
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Default Suggestion for an HF starter rig

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



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Old September 27th 07, 03:53 PM posted to rec.radio.amateur.moderated
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Default Suggestion for an HF starter rig

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 -

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Old September 27th 07, 07:27 PM posted to rec.radio.amateur.moderated
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Default Suggestion for an HF starter rig

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



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Old September 28th 07, 05:00 AM posted to rec.radio.amateur.moderated
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Default Suggestion for an HF starter rig

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

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Old September 28th 07, 02:01 PM posted to rec.radio.amateur.moderated
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Default Suggestion for an HF starter rig

wrote:

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.


That's a very good point, especially in today's world in which so many
people live in close proximity to their neighbors and there are often
restrictions on what can be erected for an antenna. My mindset tends to
be stuck back in the 60's suburbia where the biggest problem was where
the trees were in relation to the length of the skyhook desired, and no
one particularly cared if ladder line was more unsightly than coax.

This line of thinking reminded me of a rather unique antenna-related
probem that one of my childhood Elmers faced. The transmitting antenna
for one of the 100 KW clear-channel AM stations was literally in his
back yard. His antenna was a long wire that fed directly into the
shack, and he grounded it when not in use with a knife switch. When you
opened that knife switch you could literally draw a small arc of RF from
the nearby transmitter. He shunted this unwanted signal to ground
during operation with a low-pass filter, but it did create an
interesting show for us wide-eyed young visitors to his shack.

I don't know how much bypassing and other fiddling he had to do because
of the ambient RF level just from being that close to that much RF. I
wonder how many of today's hams, faced with this obstacle, would simply
decide that operation on HF was not possible.

In fact, I wonder if today's FCC restrictions on exposure to RF would
even permit houses that close to a 100 KW transmitter.

73, Steve KB9X

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Old September 28th 07, 02:22 PM posted to rec.radio.amateur.moderated
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Default Suggestion for an HF starter rig

wrote

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.


You're right. We've (I've) made assumptions of property conditions that may
not exist for the OP. My little 50 footer with ladder line was technically
in the clear, but its apex was only 7 feet above the flat roof. The
transmission line could only drop straight down for about 6 feet, then run
suspended across the top of the roof for 20 feet, then down to the shack.
Yet I worked DXCC with it, including serious long-haul, from 10 - 40 meters.
We don't know the OP's situation.

Howard N7SO


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Old September 28th 07, 02:29 PM posted to rec.radio.amateur.moderated
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wrote:
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?


That's a pretty good reason, though. 1/4 wavelength dipoles - make sure
to read that as total antenna length, not 1/4 wavelength per leg, are
just a troublesome combination that a lot of tuners can't tune very well.



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.


Pretty much the case. I would surmise that the more you have to tune
out that way off impedance, the more loss you might have. It's the old
thing about the tuner being able to match a coat hanger. I suppose so,
but it probably isn't the best way to go.

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.


They are very clever. The OCF especially is a joyful playground to work
on with antenna design programs. It is a great way to learn both the
programs and antenna theory.


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.


Often the idea of "low SWR" is put out as if it is the sole criteria. In
defense of SWR lovers, modern Rigs really hate High SWR, especially
reactance of the capacitive kind. But a 50 ohm resistor has 1.1:1 VSWR,
and some manufacturers have taken advantage of that sort of thing in the
past.

On the subject of antennas that work well on a band or two, it is sound
technical advice. The problem as I see it is that most new folks these
days start out with an "all band" radio, and are inclined to want a
antenna that is likewise all band.


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?


A lot of Western and Eastern EU, Great Britain, Iceland, Norway, most of
South/Central America, about half of Africa, Israel, Australia,
Antarctica, and a couple others. No JA or far eastern countries, but I
haven't tried really hard, I just work 'em if I happen to hear them.

I once accidentally worked a fair part of a contest once on 75 meters on
probably around 3 watts, mostly into California - I had tuned the
antenna, and forgot to turn the power back up. I had works around 25
QSO's before catching that one.

Of course, that isn't quantified data, it's just anecdotal. But running
at QRP levels does make for a more stern test of an antenna's abilities,
especially if there isn't obvious signs of it, such as not getting calls
answered. Sold me on the thing.

The technical details are that it is a 96 foot total length dipole, up
around 55 feet, the center support is a short length of pvc tubing. The
ladder line is soldered to the respective dipole wire. Ladder line makes
an almost straight drop to the Shack window. Definitely not the best
thing going, but not too bad.


- 73 de Mike KB3EIA -


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Old September 28th 07, 05:50 PM posted to rec.radio.amateur.moderated
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Default Suggestion for an HF starter rig

On Sep 28, 8:22 am, "Howard Lester" wrote:
wrote

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.


You're right. We've (I've) made assumptions of property conditions that may
not exist for the OP. (snipp)
We don't know the OP's situation.



Well, based on his call sign and the FCC's data for the address I did
a bit of detective work and found that this guy will have some unique
issues to deal with. The aerial photos of the address indicate that
there are some mature looking trees about so some random length wire
antenna may be possible. The lots seem very small compared to the
size of the houses too, what we'd call zero lot line homes in the
Texas area.

However, the most interesting thing is that it seems that he is
located in a valley with some fairly high mountains about that may
limit even the best HF antenna situation. This is clearly a problem
to the west as the QTH seems to be located on the base of the
mountains to the west.

I do like the random wire ideas though. This months QST has a brief
description of one installation of a random wire loop in an attic.
You just never quite know how these will perform until you put them up
and try. It can be discouraging if things don't work out though.

-= Bob =-




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