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

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

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

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 =-

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 -

On Sep 28, 9:29?am, Michael Coslo wrote:
wrote:
On Sep 27, 10:53?am, Michael Coslo wrote:

Why not,

[use a 1/4 wave dipole]

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.

I'm not convinced. Depending on the transmission line impedance and
length, the shack-end Z could be within the matching range
of the Transmatch.

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.

Agreed. But so are other implementations such as trap dipoles and
the classic dipole-with-ladder-line feed, where you try different
dipole and transmission-line lengths.

Often the idea of "low SWR" is put out as if it is the sole criteria.

Too often.

In
defense of SWR lovers, modern Rigs really hate High SWR,
especially
reactance of the capacitive kind.

Well, that depends on how you define 'modern'...

But a 50 ohm resistor has 1.1:1 VSWR,
and some manufacturers have taken advantage
of that sort of thing in the past.

Not just in the past. Google "Maxx-comm matcher" (try different
spellings). Those folks are still in business.

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.

Which may or may not be a good idea. If the only bands that
are open when you have time to operate are ones where your
antenna works poorly, the result is going to be frustration.

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.

On which bands?

No JA or far eastern countries, but I
haven't tried really hard, I just work 'em if I happen to hear them.

Of course from EPA, VK-land is about the antipodes.

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.

Situational awareness, that's all. With my rig, the power level is
pretty obvious.

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 Ultimate Test is "what have you worked on it?" Theory is great
but the real proof is in the QSOs.

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.

I suspect that the 96 foot length was decided because that's what
would fit in the available space.

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.

Actually, what you describe is pretty close to optimum for a simple
multiband antenna system in limited space, which I suspect is the
main issue.

Are you using true ladder line, or "window line" (Twin Lead with
holes punched in the insulation)? True ladder line (heavy wire, wide
spacing, mostly air insulation) has lower loss and less weather
effects. If the line is short there's not much difference, but as
frequency and line length increaseit can be worth changing out.

Depending on the shack-end impedances, different Transmatches
can have more or less loss. The worst-case scenario is where
a 4:1 balun is used with a shack-end impedance that has low resistive
and high reactive values. The poor Transmatch has to
try to deal with one quarter of the resistive part!

73 de Jim, N2EY

wrote:
On Sep 28, 9:29?am, Michael Coslo wrote:
wrote:
On Sep 27, 10:53?am, Michael Coslo wrote:

Why not,

[use a 1/4 wave dipole]

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.

I'm not convinced. Depending on the transmission line impedance and
length, the shack-end Z could be within the matching range
of the Transmatch.

A few years back I did a modeling of an antenna that was 1/4 wavelength
long at I think 40 meters. The SWR of the antenna was approaching
infinite. If I get the chance, I'll model it again tonight - I'm doing
the mass mailing for the PAQSO party tonight, and if all goes well, I
should have a little time.


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.

Agreed. But so are other implementations such as trap dipoles and
the classic dipole-with-ladder-line feed, where you try different
dipole and transmission-line lengths.

Often the idea of "low SWR" is put out as if it is the sole criteria.

Too often.

In
defense of SWR lovers, modern Rigs really hate High SWR,
especially
reactance of the capacitive kind.

Well, that depends on how you define 'modern'...

Non-tube? Don't get me wrong, I LOVE tube rigs.


But a 50 ohm resistor has 1.1:1 VSWR,
and some manufacturers have taken advantage
of that sort of thing in the past.

Not just in the past. Google "Maxx-comm matcher" (try different
spellings). Those folks are still in business.

That's the one I was referring to. Hard to imagine they are still doing
business.



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.

On which bands?

Mostly 20 and 40. Just a few of the near out of country neighbors on 80.


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.

I suspect that the 96 foot length was decided because that's what
would fit in the available space.

Yup, I tried a few dipoles that were longer, and made a Z shape. They
worked okay, but were a lot more maintenance. Lots of tree whipping in
storms here, and I almost made plastic pully's into the end insulators
to combat the extra movement. But I went back to the 96 foot length



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.

Actually, what you describe is pretty close to optimum for a simple
multiband antenna system in limited space, which I suspect is the
main issue.

I agree. What really surprised me was that the performance on 75 meters
was pretty acceptable. I mostly get down there during contests, and have
had nice results. Worked enough people to make it worthwhile.



Are you using true ladder line, or "window line" (Twin Lead with
holes punched in the insulation)? True ladder line (heavy wire, wide
spacing, mostly air insulation) has lower loss and less weather
effects. If the line is short there's not much difference, but as
frequency and line length increase it can be worth changing out.

I use the window line. I have heard of the advantages of the true ladder
line, and certainly the higher impedance is one of them. I've heard of
some of the drawbacks of window line, such as it's performance when wet.

I did take issue with the test method cited by many, in which the window
line was dunked in water that included a wetting agent. My contention is
that the experiment showed the effects on window line with wetted line.

My experience has been that window line does not wet in this manner.
When the experimenter has to add a chemical to coat the line with water,
it is altering the conditions and producing results germane to only
those conditions.

I wonder what would happen to open wire ladder line under those conditions?

"Michael Coslo" wrote

A few years back I did a modeling of an antenna that was 1/4 wavelength
long at I think 40 meters. The SWR of the antenna was approaching
infinite. If I get the chance, I'll model it again tonight - I'm doing the
mass mailing for the PAQSO party tonight, and if all goes well, I should
have a little time.

I'd think a strict 1/4 wave, regardless how it's fed, would be pretty
horrific on that specific band. (But I couldn't explain why...it's just from
what I've read.) That's why I made mine (55 feet) so that it was under 1/4
wave for 40, and more than 1/4 for all the higher bands.

As for window line being affected by water... yes, it is, but I never found
it a big deal. As I recall, I just retuned some of the transmatch settings
to accommodate. I used both 450 and 300 ohm window line... and even tv
twinlead. What fun I had one night when I heard a cat playing on my flat
roof, and I could tell he was playing with the transmission line that was
suspended about a foot off the roof... I transmitted 100 watts and heard him
take off like a shot!

BTW, I wonder what happened to the OP? Did we drive him away? ;-)

Howard N7SO

On Oct 2, 3:20?pm, Michael Coslo wrote:
wrote:
On Sep 28, 9:29?am, Michael Coslo wrote:

Depending on the transmission line impedance and
length, the shack-end Z could be within the matching range
of the Transmatch.

A few years back I did a modeling of an antenna that was 1/4
wavelength
long at I think 40 meters. The SWR of the antenna was
approaching infinite.

???

With reference to what sort of feedline? SWR only has meaning
wrt a particular line impedance.

If I get the chance, I'll model it again tonight -

TNX

In
defense of SWR lovers, modern Rigs really hate High SWR,
especially
reactance of the capacitive kind.

Well, that depends on how you define 'modern'...

Non-tube? Don't get me wrong, I LOVE tube rigs.

There have been non-tube ham rigs for a couple decades now....

In a way, we have come full circle.

Look back 50-odd years, and most ham rigs could match
an SWR of 3 or 4 to 1 without a tuner, because they had fairly
wide-range pi-networks.

That was sacrificed to the desire for miniaturization, but even as
late as the early 1980s, there were rigs with tube finals that could
match 2:1 SWR or so.

Meanwhile the SS rigs wanted 50 + j0 loads for their no-tune finals,
so Transmatches became very common - so common, that rigs began to
offer them built-in, so the rig could match SWR of 3 or 4 to 1. Only
difference was automation.

The more things change....

Google "Maxx-comm matcher" (try different
spellings). Those folks are still in business.

That's the one I was referring to. Hard to imagine they are still
doing business.

The ARRL Product Review where they tested one, then X-rayed
it and opened it up to show the resistors was well over 20 years
ago.

The fact of the matter is that they *do* work - just not very well.

Mostly 20 and 40. Just a few of the near out of country
neighbors on 80.

WInter nights are coming. That's when 80 and 40 really come into
their own.

I suspect that the 96 foot length was decided because
that's what
would fit in the available space.

Yup, I tried a few dipoles that were longer, and made a
Z shape. They
worked okay, but were a lot more maintenance.
Lots of tree whipping in
storms here, and I almost made plastic pully's into the end
insulators
to combat the extra movement. But I went back to the
96 foot length

IMHO, amateur radio antenna design is no more than
10% electrical engineering and no less than 90%
mechanical engineering. In many cases it's 5%/95%.

Actually, what you describe is pretty close to
optimum for a simple
multiband antenna system in limited space, which
I suspect is the
main issue.

I agree. What really surprised me was that the performance
on 75 meters
was pretty acceptable.

Not really a surprise to me. While short, the 96 footer and lowloss
feed system will put significant RF in usable directions.

I mostly get down there during contests, and have
had nice results. Worked enough people to make it worthwhile.

CW SS is a month away....

Are you using true ladder line, or "window line" (Twin Lead with
holes punched in the insulation)? True ladder line
(heavy wire, wide
spacing, mostly air insulation) has lower loss and less weather
effects. If the line is short there's not much difference, but as
frequency and line length increase it can be worth changing out.

I use the window line. I have heard of the advantages of the true
ladder
line, and certainly the higher impedance is one of them.

Higher impedance in and of itself doesn't make the difference.
What matters is the lower loss due to more copper and less
dielectric.

The ocarc transmission line loss calculator does balanced lines as
well as coax.

I've heard of
some of the drawbacks of window line, such as it's performance when wet.

I did take issue with the test method cited by many, in which
the window
line was dunked in water that included a wetting agent.
My contention is
that the experiment showed the effects on window line with
wetted line.

My experience has been that window line does not wet
in this manner.
When the experimenter has to add a chemical to coat
the line with water,
it is altering the conditions and producing results germane to only
those conditions.

I agree. A spray with the garden hose will adequately simulate a
rainy day, I think.

I think your biggest possible improvement would be to
see how lossy your tuner/transmission line combo really is, and
improve it if possible.

73 de Jim, N2EY