I am very very proud that I hung a 80-Meter dipole about 100 feet
above my QTH last week.

But I also had a hankering to cover 40 Meters with it too (although I
already had a 40 Meter dipole). So the section in the antenna book
about fan dipoles came to mind.

I looked in the ARRL antenna book, it told me that the seperation of
wires was not all that important. So I sort-of duplicated one of the
sketches in the book, and hung the 40 meter wire from an tiny little
egg insulator on the 80 meter wire.

Result: DID NOT WORK AT ALL. No indication of any kind of antenna
resonance anywere from 5 to 9 MHz. Sky-high SWR over the whole range.
It didn't mess up 80-meter operation, though.

Looked at W4RNL's "My Top 5 Backyard Multi-Band Antennas". The fan
dipole is in there, but not in the way it looked in the ARRL book. He
says you need a big spacer at the end of the line, like 10 feet, to
get consistent results. He has some other notes about modeling Fan
dipoles at http://www.antennex.com/w4rnl/col0507/amod111.html I give
it a shot, and holy moly, it looks like this should work. Maybe some
bigger spacing would result in a bit more bandwidth but I'm mostly
working at the bottom of the CW band.

So I'm going to find some skinny 10-foot fiberglass poles and try re-
rigging this weekend.

Tim N3QE

Tim Shoppa wrote:
I am very very proud that I hung a 80-Meter dipole about 100 feet
above my QTH last week.

But I also had a hankering to cover 40 Meters with it too (although I
already had a 40 Meter dipole). So the section in the antenna book
about fan dipoles came to mind.

Feed it with 450 ohm ladder-line and you can cover 40m
simply by changing the length of the ladder-line with
no tuner required. Please reference:

http://www.w5dxp.com/notuner.htm
--
73, Cecil http://www.w5dxp.com

On Nov 2, 2:54 pm, Tim Shoppa wrote:
I am very very proud that I hung a 80-Meter dipole about 100 feet
above my QTH last week.

But I also had a hankering to cover 40 Meters with it too (although I
already had a 40 Meter dipole). So the section in the antenna book
about fan dipoles came to mind.

I looked in the ARRL antenna book, it told me that the seperation of
wires was not all that important. So I sort-of duplicated one of the
sketches in the book, and hung the 40 meter wire from an tiny little
egg insulator on the 80 meter wire.


I've been running those for years. Placing the wires closely together
is a problem as far as coupling, and it almost always effects the
higher of the used bands.
The best way to orient is at right angles, if looking from overhead.
At right angles, there is basically no interaction at all, and the
dipoles act pretty much the same as if separate.
In fact, I've had legs fall down and have no effect on the other
bands. The closer the wires, the more coupling, and the more
tweaking you will have to do to get the higher band tuned.
I've even seen cases where the higher band would tune
a higher frequency by adding more wire. Exactly the opposite
from normal. I don't really like having the wires in the same plane
at all, but if no choice, I would use as large a spreader as possible.
I often have multiple bands.. Here at the house, I presently have
an 80m turnstile, and a 40 dipole on the same feedline.
At my place in OK, I have 160,80,40 and 20m on the same coax
feed. All wires spread as far apart as possible. Looks like a big
spider from overhead.
MK

Here's the deal. If you put the wires close together you get a lot of
interaction. The manifestation of the interaction is that the
higher-frequency dipoles end up considerably shorter than normal, and
they'll have a narrower bandwidth than an isolated dipole. The longest
one will also be affected by the others, but not nearly so much. You'll
also find that small differences in spacing can have quite an effect on
the dipole resonant frequencies, which is why a cookbook approach
usually doesn't work unless the writer is very careful to document the
antenna accurately and you're extremely careful to exactly duplicate it.
But you just about always end up having to tune it.

Tuning a close-spaced multiple dipole like this is time consuming. You
begin by adjusting the length of the longest one to resonance. Then you
adjust the next shorter one, and so forth. It might be necessary to
repeat the process after the first time through. And, as I mentioned,
you'll end up with some pretty narrowbanded antennas, and the lengths
won't be what common formulas predict.

The interaction decreases rapidly as you spread the dipoles apart. If
you can get them around 30 degrees apart, the interaction is minimal and
you can just about treat them like separate dipoles. A lot of
installations fall between these extremes, so the dipoles have some
interaction but it's not as severe as it is when they're very closely
spaced.

Roy Lewallen, W7EL

Roy Lewallen wrote:
SNIP

Tuning a close-spaced multiple dipole like this is time consuming. You
begin by adjusting the length of the longest one to resonance. Then you
adjust the next shorter one, and so forth. It might be necessary to
repeat the process after the first time through. And, as I mentioned,
you'll end up with some pretty narrowbanded antennas, and the lengths
won't be what common formulas predict.

The interaction decreases rapidly as you spread the dipoles apart. If
you can get them around 30 degrees apart, the interaction is minimal and
you can just about treat them like separate dipoles. A lot of
installations fall between these extremes, so the dipoles have some
interaction but it's not as severe as it is when they're very closely
spaced.

Roy Lewallen, W7EL

Roy,

My experience confirms what you report except for the bandwidth but
I did use a balun. My elements are spaced about 7 inches apart and
run parallel to each other. The elements are for 10, 15, 17, 20 & 40
metres with pretty effective operation on 6 and 12.

You can see the figures for the elements he
http://www.radiowymsey.org/FanDipole/FanDipole.html

Charlie.

--
M0WYM
www.radiowymsey.org

On Nov 2, 6:12 pm, Roy Lewallen wrote:
Here's the deal. If you put the wires close together you get a lot of
interaction. The manifestation of the interaction is that the
higher-frequency dipoles end up considerably shorter than normal, and
they'll have a narrower bandwidth than an isolated dipole. The longest
one will also be affected by the others, but not nearly so much. You'll
also find that small differences in spacing can have quite an effect on
the dipole resonant frequencies, which is why a cookbook approach
usually doesn't work unless the writer is very careful to document the
antenna accurately and you're extremely careful to exactly duplicate it.

I had read the points you make above in the antenna books... but did
not realize exactly how variable the effects are especially for the
cases where the elements are physically close. The examples in the
ARRL Antenna book are particularly heinous: they show elements
separated by a fraction of an inch (e.g. the twin-lead example, the
picture that shows the wires hanging from egg insulators) and these
examples are - from my experiments - the least likely to work at all.

The interaction decreases rapidly as you spread the dipoles apart. If
you can get them around 30 degrees apart, the interaction is minimal and
you can just about treat them like separate dipoles. A lot of
installations fall between these extremes, so the dipoles have some
interaction but it's not as severe as it is when they're very closely
spaced.

This is a very fundamental piece of wisdom, and a piece that deserves
more attention in the ARRL Antenna books. The current statement - "The
separation between the dipoles for the various frequencies does not
seem to be especially critical" is incredibly wrong for the close-
spaced exampls shown in the book.

Tim.

On 5 Nov, 06:03, Tim Shoppa wrote:
On Nov 2, 6:12 pm, Roy Lewallen wrote:

Here's the deal. If you put the wires close together you get a lot of
interaction. The manifestation of the interaction is that the
higher-frequency dipoles end up considerably shorter than normal, and
they'll have a narrower bandwidth than an isolated dipole. The longest
one will also be affected by the others, but not nearly so much. You'll
also find that small differences in spacing can have quite an effect on
the dipole resonant frequencies, which is why a cookbook approach
usually doesn't work unless the writer is very careful to document the
antenna accurately and you're extremely careful to exactly duplicate it.

I had read the points you make above in the antenna books... but did
not realize exactly how variable the effects are especially for the
cases where the elements are physically close. The examples in the
ARRL Antenna book are particularly heinous: they show elements
separated by a fraction of an inch (e.g. the twin-lead example, the
picture that shows the wires hanging from egg insulators) and these
examples are - from my experiments - the least likely to work at all.

The interaction decreases rapidly as you spread the dipoles apart. If
you can get them around 30 degrees apart, the interaction is minimal and
you can just about treat them like separate dipoles. A lot of
installations fall between these extremes, so the dipoles have some
interaction but it's not as severe as it is when they're very closely
spaced.

This is a very fundamental piece of wisdom, and a piece that deserves
more attention in the ARRL Antenna books. The current statement - "The
separation between the dipoles for the various frequencies does not
seem to be especially critical" is incredibly wrong for the close-
spaced exampls shown in the book.

Tim.

After you have read the books try some thing different.
Obtain insulated wire and double it over itself to form a single
wire combination. Wind a considerable length on a former.
Using a MFJ analyser run thru the frequencies until you obtain a
resonance
at a reasonable impedance level and then scale for your desired
frequency.
Of course you must connect the MFJ to the two wire ends.
If you don't succeed first time around then short the wires in
increments
till you succeed.Wires close together can be turned into advantage if
you
go along with mother nature!
To make things easier, heat the insulation on the wire and insert
small needles
so you can hook up the MFJ at different turn lengths.
Be a leader not a follower
Art KB9MZ....XG

"art" wrote in message
oups.com...
On 5 Nov, 06:03, Tim Shoppa wrote:
On Nov 2, 6:12 pm, Roy Lewallen wrote:

Here's the deal. If you put the wires close together you get a lot of
interaction. The manifestation of the interaction is that the
higher-frequency dipoles end up considerably shorter than normal, and
they'll have a narrower bandwidth than an isolated dipole. The longest
one will also be affected by the others, but not nearly so much. You'll
also find that small differences in spacing can have quite an effect on
the dipole resonant frequencies, which is why a cookbook approach
usually doesn't work unless the writer is very careful to document the
antenna accurately and you're extremely careful to exactly duplicate
it.

I had read the points you make above in the antenna books... but did
not realize exactly how variable the effects are especially for the
cases where the elements are physically close. The examples in the
ARRL Antenna book are particularly heinous: they show elements
separated by a fraction of an inch (e.g. the twin-lead example, the
picture that shows the wires hanging from egg insulators) and these
examples are - from my experiments - the least likely to work at all.

The interaction decreases rapidly as you spread the dipoles apart. If
you can get them around 30 degrees apart, the interaction is minimal
and
you can just about treat them like separate dipoles. A lot of
installations fall between these extremes, so the dipoles have some
interaction but it's not as severe as it is when they're very closely
spaced.

This is a very fundamental piece of wisdom, and a piece that deserves
more attention in the ARRL Antenna books. The current statement - "The
separation between the dipoles for the various frequencies does not
seem to be especially critical" is incredibly wrong for the close-
spaced exampls shown in the book.

Tim.

After you have read the books try some thing different.
Obtain insulated wire and double it over itself to form a single
wire combination. Wind a considerable length on a former.
Using a MFJ analyser run thru the frequencies until you obtain a
resonance
at a reasonable impedance level and then scale for your desired
frequency.
Of course you must connect the MFJ to the two wire ends.
If you don't succeed first time around then short the wires in
increments
till you succeed.Wires close together can be turned into advantage if
you
go along with mother nature!
To make things easier, heat the insulation on the wire and insert
small needles
so you can hook up the MFJ at different turn lengths.
Be a leader not a follower
Art KB9MZ....XG

why mfj? we using another brand, can we? :-)

On Mon, 05 Nov 2007 06:03:55 -0800, Tim Shoppa
wrote:

The examples in the
ARRL Antenna book are particularly heinous: they show elements
separated by a fraction of an inch (e.g. the twin-lead example, the
picture that shows the wires hanging from egg insulators) and these
examples are - from my experiments - the least likely to work at all.

I have been complaining about that particular example in the ARRL
books for years.

I am beginning to think that you & I are the only ones to try to make
it work!

I just had a moment of inspiration...I wonder why I have not modeled
it in EZNEC? Maybe later this evening...

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"

Tim,

I run a fan dipole from 6 to 40 metres in my loft, I only run QRP
but with my 10 watts of SSB I have worked Canada, America and North
Africa from England.

There is no reason why the aerial could not be outside at some other
QTH.

You will find details he
http://www.radiowymsey.org/FanDipole/fandiploe.htm .


Charlie.


--
M0WYM
www.radiowymsey.org