I want to make a random-length inverted-V for general listening and
perhaps, maybe, occasional HF work, no pretense to have perfect match
or minimum losses. I see much discussion about feeding a random dipole
with 450 or 600 ohm ladder line.

I can lay a low loss 75 ohm line but absolutely not a ladder line, so
I'd have to put a balun at the apex

I'd cut a dipole of about 15 + 15 m (50+50 ft), 120 deg. inverted V,
apex at 15 m.

I could do 1:4 - 300 ohm or 1:9 - 625 ohm.

What would be the least-bad?

Thanks in advance!

On Nov 6, 10:39*am, spamhog wrote:
I want to make a random-length inverted-V for general listening and
perhaps, maybe, occasional HF work, no pretense to have perfect match
or minimum losses. I see much discussion about feeding a random dipole
with 450 or 600 ohm ladder line.

I can lay a low loss 75 ohm line but absolutely not a ladder line, so
I'd have to put a balun at the apex

I'd cut a dipole of about 15 + 15 m (50+50 ft), 120 deg. inverted V,
apex at 15 m.

I could do 1:4 - 300 ohm or 1:9 - 625 ohm.

What would be the least-bad?

Thanks in advance!

just wind a coil choke, that will be cheaper and no worse than either
of those options.

On Sat, 6 Nov 2010 03:39:36 -0700 (PDT), spamhog
wrote:

no pretense to have perfect match
or minimum losses.

And then you recite a number of matching options.

What do you REALLY want?

73's
Richard Clark, KB7QHC

K1TTT
just wind a coil choke

Richard
What do you REALLY want?

There is a difference between a 12:1 and a 3:1 mismatch, especially in
a long coax run. What I want is a rough mid-of-the-range estimate of
where impedance in a 50'+50' squat inverted-V dipole across say
3-20MHz.

There is a gazillion description of such antennas fed via 450 ohm
ladder lines, and a few with 600 ohm lines:
- ready made 450 ohm plastic clad line is commercially available
- 600 ohm line can be made with commercially available spacers for
standard wire gauges.

Neither suggests that the corresponding impedance is a good midpoint.
The advantage of ladder lines is extremely low loss, allowing for
massive mismatches without much loss due to the exponentially-
decreasing but still substantial backwave.

Being forced to use a coax, I am looking for a ballpark match not
inspired by the current commercial availability of things I am not
going to include in the design.

The random dipole and the T2FD and related antennas ( like the
ubiquitous 3-wire damped dipole sold by many companies for
professional use) are operationally somewhat similar. All are
compromise antennas usable in a large spectrum, all are rather funny
in terms of losses, radiation efficiency, and radiation pattern.

The damping resistor is there exclusively to smooth the response over
the spectrum, at a cost. One could even argue that a balun+coax fed
tuned random dipole and an untuned T2FD of roughly similar size
exhibit similar losses, ^cept one heats the coax more (once the ATU is
peaked), and the other heats the resistor more, which should be handy
in determining deicing strategies. ;-)

There is plenty of literature, including some baseline simulations,
for the T2FD etc.. I haven't found the same for inverted-V random
dipoles. Any pointers? Have I been googling for the wrong things?

"spamhog" wrote in message
...
K1TTT
just wind a coil choke

Richard
What do you REALLY want?

There is a difference between a 12:1 and a 3:1 mismatch, especially in
a long coax run. What I want is a rough mid-of-the-range estimate of
where impedance in a 50'+50' squat inverted-V dipole across say
3-20MHz.

There is a gazillion description of such antennas fed via 450 ohm
ladder lines, and a few with 600 ohm lines:
- ready made 450 ohm plastic clad line is commercially available
- 600 ohm line can be made with commercially available spacers for
standard wire gauges.

Neither suggests that the corresponding impedance is a good midpoint.
The advantage of ladder lines is extremely low loss, allowing for
massive mismatches without much loss due to the exponentially-
decreasing but still substantial backwave.

Being forced to use a coax, I am looking for a ballpark match not
inspired by the current commercial availability of things I am not
going to include in the design.

The random dipole and the T2FD and related antennas ( like the
ubiquitous 3-wire damped dipole sold by many companies for
professional use) are operationally somewhat similar. All are
compromise antennas usable in a large spectrum, all are rather funny
in terms of losses, radiation efficiency, and radiation pattern.

The damping resistor is there exclusively to smooth the response over
the spectrum, at a cost. One could even argue that a balun+coax fed
tuned random dipole and an untuned T2FD of roughly similar size
exhibit similar losses, ^cept one heats the coax more (once the ATU is
peaked), and the other heats the resistor more, which should be handy
in determining deicing strategies. ;-)

There is plenty of literature, including some baseline simulations,
for the T2FD etc.. I haven't found the same for inverted-V random
dipoles. Any pointers? Have I been googling for the wrong things?




If you are going to feed the dipole with coax, there is no balun ratio that
would work over the whole range. I would say the best you can do is make it
into the G5RV type antenna if 100 feet is about all you have to work with.
I do not like the G5RV antennas, but for those that must make a big
compromise system, it is one way to go.
If you must use coax, you may also want to look at getting some of the
highest impedance coax you can find. Around 100 ohms if you can find any.
Then feed the antenna with two runs of it. I am thinking that you just use
the center conductors hooked to the dipole ends. Then treat it like open
wire and feed it with a tuner.

If you are going to feed the dipole with coax, there is no balun ratio that
would work over the whole range.

If you must use coax, you may also want to look at getting some of the
highest impedance coax you can find.

I humbly and apologetically decline to comment and, hereby, of course,
deviously venture obliquously to imply that the customary norm of duly
perusing an interrogative ponderation, previously consigned to a
written medium of unrestricted admittance, ahead of proffering a reply
thereto, which in turn will be inscribed for posterity to gape at,
cannot wantonly be construed to be peculiarly fraught with some
unnamed yet capital order of detriment. :-)

On Tue, 9 Nov 2010 01:48:16 -0800 (PST), spamhog
wrote:

Have I been googling for the wrong things?

None of these issues seriously impacts the simplicity of your initial
request, but your elaborations of anticipating grief are numerous.

What do you REALLY want?

73's
Richard Clark, KB7QHC

What do you REALLY want?

73's
Richard Clark, KB7QHC

Dear Richard,

My question is very simple:

I'd cut a dipole of about 15 + 15 m (50+50 ft), 120 deg. inverted V,
apex at 15 m.
I could do 1:4 - 300 ohm or 1:9 - 625 ohm.
What would be the least-bad?

If you can't or won't tell if such an antenna very roughly better
matches a 300 or 600+ ohm source over the HF spectrum,, what else
can I do but
- turn on EZNEC and start playing
- build two or more transformers and send someone up at the 50ft apex
and swap them in sequence while I do in vivo comparisons and pollute
the spectrum
- wait for someone else to answer or to point me to a good URI?

I can live with it.

I might also put together the rather long list of authors of articles
on the subject and ask them on your behalf what they really really
want if they have to feed the thing with a coax instead of ladder
lines of the commercially available impedances and want the least
lossy solution among the available alternatives. :-)

73 es tnx de n1jpr/i2

On Wed, 10 Nov 2010 04:33:31 -0800 (PST), spamhog
wrote:

What do you REALLY want?

73's
Richard Clark, KB7QHC

Dear Richard,

My question is very simple:

I'd cut a dipole of about 15 + 15 m (50+50 ft), 120 deg. inverted V,
apex at 15 m.
I could do 1:4 - 300 ohm or 1:9 - 625 ohm.
What would be the least-bad?

If you can't or won't tell if such an antenna very roughly better
matches a 300 or 600+ ohm source over the HF spectrum,, what else
can I do but
- turn on EZNEC and start playing

You keep repeating what you have. Can't or won't telling is still a
matter of

What do you really want?

You are forcing this into my trying to read between the lines and
guessing, so here goes:

- in spite of demurring about
no pretense to have perfect match
or minimum losses.
You "want" something with a near-perfect match and near-minimum losses
"over the HF spectrum."

This is dreaming in technicolor and 5.1 Dolby sound.

This is a technical forum and the expectation is that you provide a
range of acceptable match and a range of acceptable loss enumerated by
the frequencies of interest. You show no concern for directionality
which will be wildly variable. In other words, something quantifiable
is needed or you are doomed to inaccurate response or tedious
instruction (such as mine). Qualified statements are suited only for
cheap sales brochures.

To your credit, you enumerate the particulars of your antenna and to
some extent the working band: 3MHz to 30MHz. However, even on first
glance, such an antenna is NOT suited for covering the entire HF
region. This should have been a minimum observation in your readings,
and the absence of its discussion by you means you either have poor
sources, or you are prepared to abandon this antenna's use on some
bands (do your sources tell you were it is going to fail miserably?).
The use of BalUns is not a solution to this and the solution, such as
it is with a Hi-Z resonator, forces problems into the other bands.
This too should be a minimum observation available from your reading
material.

I might also put together the rather long list of authors of articles
on the subject and ask them on your behalf what they really really
want if they have to feed the thing with a coax instead of ladder
lines of the commercially available impedances and want the least
lossy solution among the available alternatives. :-)

Try googling the terms "wide band" "hf antenna" and writing to the
2,960 authors.

This board is innundated with claims and testimonials to those designs
all the time - such freely available "articles" do not constitute
evidence nor bring legitimacy.

There is one very simple, logical test for the answer to your unstated
question - if you can't buy or find one, why do you think it exists or
can be so easily assembled?

73's
Richard Clark, KB7QHC

On 11/9/2010 10:19 AM, spamhog wrote:

If you are going to feed the dipole with coax, there is no balun ratio that
would work over the whole range.

If you must use coax, you may also want to look at getting some of the
highest impedance coax you can find.

I humbly and apologetically decline to comment and, hereby, of course,
deviously venture obliquously to imply that the customary norm of duly
perusing an interrogative ponderation, previously consigned to a
written medium of unrestricted admittance, ahead of proffering a reply
thereto, which in turn will be inscribed for posterity to gape at,
cannot wantonly be construed to be peculiarly fraught with some
unnamed yet capital order of detriment. :-)

Careful, some people here are offended by your type of response.

I can think of several.

tom
K0TAR