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On 3 May,
wrote:

I was refering to the case where there is nothing to adjust the match and
getting something under 3:1 at the end of the feed line.

It was well within 1.5:1 within (part of) 10 and 12m bands.



Given an ATU, you can usually match anything and there is no need for the
physical complexity of a fan dipole.

Very true The ATU is only used for 15,17 and 20, but my (larger) doublet
with tuned feeders is better for 20 and 17, and about the same for 15.

I'm currently debating whether to add additional dipoles to the fan or
replace it with a smaller doublet (about a half wave on 20), which would be
about half the size of the existing doublet.

I may end up trying both, I doubt if there will be much difference apart from
a slight change in directivity.

--
BD
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wrote:
On 1 May,
wrote:

FYI I spent an afternoon with EZNEC exploring fan dipoles.

What I found was the farther apart the wires, the less the interaction,
which is what one would expect from common sense.

From my limited runs it appears that somewhere around 20 degrees is about
where the minimum separation needs to be for practical length
adjustments.

At angles less than that be prepared to spend a lot of time pruning.

It doesn't matter if the wires are separated vertically or horizontally
other than horizontal separatation means you need lots of support points.

If the bands are too close together, i.e. 20-17, 17-15, 12-10, you can
never get both bands to "work", i.e. a decent match.

I've got 12 and 10 working fine together, seperated by about 8" giving a
decent match. It also works fine on 15 although no wires for 15, but a
short
coax (20') to an ATU. It has a "pawsey stub" balun cut for about 17m
(modeled
with NEC for best match with fan dipoles for all bands 20 -10, but I
haven't
as yet got round to dipoles for 15 and below).

# I was refering to the case where there is nothing to adjust the match and
# getting something under 3:1 at the end of the feed line.
#
# Given an ATU, you can usually match anything and there is no need for the
# physical complexity of a fan dipole.

An open wire fed dipole would give pretty good performance. But, feeding
such an antenna with RG-8 and living with a high VSWR (maybe up to 10:1)
shouldn't be discarded.

A dipole of about 18 feet would cover 24 and 28 MHz with about 5:1
VSWR....not bad.

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Wayne wrote:


wrote in message ...

wrote:
On 1 May,
wrote:



# I was refering to the case where there is nothing to adjust the match and
# getting something under 3:1 at the end of the feed line.
#
# Given an ATU, you can usually match anything and there is no need for the
# physical complexity of a fan dipole.

An open wire fed dipole would give pretty good performance. But, feeding
such an antenna with RG-8 and living with a high VSWR (maybe up to 10:1)
shouldn't be discarded.

A dipole of about 18 feet would cover 24 and 28 MHz with about 5:1
VSWR....not bad.

My transmitter gives up at about 5:1.

Your milage (and transmitter) may vary.

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wrote in message ...

Wayne wrote:


wrote in message ...

wrote:
On 1 May,
wrote:



# I was refering to the case where there is nothing to adjust the match
and
# getting something under 3:1 at the end of the feed line.
#
# Given an ATU, you can usually match anything and there is no need for
the
# physical complexity of a fan dipole.

An open wire fed dipole would give pretty good performance. But, feeding
such an antenna with RG-8 and living with a high VSWR (maybe up to 10:1)
shouldn't be discarded.

A dipole of about 18 feet would cover 24 and 28 MHz with about 5:1
VSWR....not bad.

# My transmitter gives up at about 5:1.

# Your milage (and transmitter) may vary.

Yes. My Yaesu ATU gives up at 5:1, so I have been using a more robust
homebrew tuner.

A VSWR of up to say 10:1 (perhaps 15:1) shouldn't be a deal killer, if you
can match the coax and are willing to accept 2-3 dB of loss. This opens up
a lot of antenna possibilities that might be otherwise discarded.

Out in the YARD, on top of 30' of 1.25 inch semi rigid conduit I have a Solorcon A99 that looked like a fussy Popsicle stick that a friend of mine gave to me that I painted with some dollar general store paint - which tunes up with the internal antenna tuner in my Kenwood TS 590S - which is below 2:1 on 10 / 12 / 15 / and 17 even without the tuner - as long as you stay within the bands - 28.300 - 28.500 etc.... And will tune up beyond that - 26.950 / 29.690 MHz with the internal tuner...

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Wayne wrote:


wrote in message ...

Wayne wrote:


wrote in message ...

wrote:
On 1 May,
wrote:



# I was refering to the case where there is nothing to adjust the match
and
# getting something under 3:1 at the end of the feed line.
#
# Given an ATU, you can usually match anything and there is no need for
the
# physical complexity of a fan dipole.

An open wire fed dipole would give pretty good performance. But, feeding
such an antenna with RG-8 and living with a high VSWR (maybe up to 10:1)
shouldn't be discarded.

A dipole of about 18 feet would cover 24 and 28 MHz with about 5:1
VSWR....not bad.

# My transmitter gives up at about 5:1.

# Your milage (and transmitter) may vary.

Yes. My Yaesu ATU gives up at 5:1, so I have been using a more robust
homebrew tuner.

A VSWR of up to say 10:1 (perhaps 15:1) shouldn't be a deal killer, if you
can match the coax and are willing to accept 2-3 dB of loss. This opens up
a lot of antenna possibilities that might be otherwise discarded.

Well, my trap inverted vee for 40-30-20-15-10 has a SWR of less than 2:1
where all my interests lie, and less than 1.5:1 on most bands.

Then there is the vertical that currently covers 160-10 at less than 1.3:1
on all frequencies for the days when I want to do something different.

It started out as about 33 feet of tubing for 40.

Wanting more, I built an enclosure containing a pair of relays and loading
coils so it was less than 2:1 on the areas of interest on 160 and 80.

Wanting more, I mounted a SGC autotuner at the base so it is always 1.3:1
or less on all bands.

EZNEC analysis says the lobes are low, and actually have some low angle
gain on 15 and 17, until I get to 12 and 10, where the lobes start pointing
to the sky.

The next modification will likely be finding a 10 M trap at a swap meet
and installing it at about 5/8 wavelengths to push the 10 M lobe down.

I can live without perfection on 12.

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wrote in message
...
Jeff Liebermann wrote:

snip


FYI I spent an afternoon with EZNEC exploring fan dipoles.

What I found was the farther apart the wires, the less the interaction,
which is what one would expect from common sense.

From my limited runs it appears that somewhere around 20 degrees is about
where the minimum separation needs to be for practical length adjustments.

At angles less than that be prepared to spend a lot of time pruning.

It doesn't matter if the wires are separated vertically or horizontally
other than horizontal separatation means you need lots of support points.

If the bands are too close together, i.e. 20-17, 17-15, 12-10, you can

I had a 10-20 fan dipole laying on a roof for a while. Matched OK after a
bit of pruning but I abandoned it when I found both bands were better with
antennas that were clear of the roof.

I wonder something (and I suppose I'll have to try it, now) : Say I had a
20m horizontal dipole up at 30 feet, could I feed it through a coax that had
a Tee-connector located 22 feet up and simultaneously feed a 15m antenna
from that Tee-connector?

Just as they would be in parallel as a true fan dipole with a common feed
point, so also would they be in parallel -- just not sharing a common feed
point.

Normally I avoid Tee-connectors because they introduce the Evil Mismatch but
this time ...

I can see one problem already; some of the 15m energy that divides at the
Tee-connector would go up to the 20m antenna and be partially radiated and
partially reflected. Standing waves. The coax length would alter the
effect.

"Sal"

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On 5/1/2012 12:43 PM, wrote:

FYI I spent an afternoon with EZNEC exploring fan dipoles.

I've used those for many years.. Probably my #1 most used antenna.
I have them here at the house, and also up in the country at
the recreational living center.


What I found was the farther apart the wires, the less the interaction,
which is what one would expect from common sense.

Yep, and if at right angles, there is virtually no interaction at all.
I've had cases with dipoles at right angles where one leg broke off,
and the SWR for the unbroken intact dipole did not change.


From my limited runs it appears that somewhere around 20 degrees is about
where the minimum separation needs to be for practical length adjustments.

At angles less than that be prepared to spend a lot of time pruning.

yep, and it can get weird.. IE: the tuning appears to work backwards
from the norm.. It will almost always be one of the higher bands that
is effected. Rarely the lower band. And in many cases, you will end
up adding wire to the higher band dipole, to come up the band. A bit
peculiar, but I've seen it many times.


It doesn't matter if the wires are separated vertically or horizontally
other than horizontal separatation means you need lots of support points.

If the bands are too close together, i.e. 20-17, 17-15, 12-10, you can
never get both bands to "work", i.e. a decent match.

Not sure if I agree with that. I would think it *should* work if the
two dipoles are at right angles. And likely good nuff for gov work,
even if at a closer angle.
But it's not something I've really tested, as I generally don't worry
about the higher bands, and tend to load the lower band wires on the
higher bands. I rarely ever string dipoles for 17,15,12,or 10..
The 40 meter legs pretty much cover 15m for instance.. I've never added
15m legs, as I always have 40 legs.. I have often added 20m legs though,
as the 40m as a half wave on 20 is the pits when coax fed.. :(



That appears to be also true for trap antennas from some limited EZNEC
modeling.

Of course, there is always the alternative of throwing technology and
money at the problem and just put up whatever wire you can and put an
autotuner up.

Yep.. But I've always like the parallel fed dipoles.
It's almost a perfect system. When tuned and operated correctly, the
dipoles function pretty much the same as single band dipoles, with
no tuner needed, and pretty much the same efficiency as a single band
dipole fed with coax. For multi band use, it's more efficient than
most any other scheme I can think of as far as the bands that have
dipoles, or have a good match for other reasons. IE: 3/4 wave resonance.
The one here at the house is 80/40/20. The one up in the country is
80 and 40. I did also have 160m legs on that one at one time, but a
storm whacked it out, and when I rebuilt it, I didn't bother with the
160m legs.
If I want to use a higher band, I use a tuner and accept the small
loss.. I actually don't get on the higher bands much.. I'm on 40 in
the day, and 80 at night most all of the time. Also 160 at night if
I have it, but that is a bit seasonal.. You won't see me on 160 much
in the summer.. So much noise, you really need an amp, and none of the
amps I have work 160m.