Building something a bit like this :
http://www.hamuniverse.com/multidipole.html

He suggests setting up one wire at a time starting with the longest, is that
the easy way ?

I would think adding all wires, a bit too long , and then starting the
adjustment with the shortest would be better ?
All the other wires overlap the shortest 100%, so I would imagine later
trimming of longer wires i parallell would not affect the short wire much.




/JS

On Tue, 3 May 2005 18:41:17 +0200, ".J.S..."
wrote:

Building something a bit like this :
http://www.hamuniverse.com/multidipole.html

He suggests setting up one wire at a time starting with the longest, is that
the easy way ?

I would think adding all wires, a bit too long , and then starting the
adjustment with the shortest would be better ?
All the other wires overlap the shortest 100%, so I would imagine later
trimming of longer wires i parallell would not affect the short wire much.

You are placing far too much importance on your objective of having
each dipole resonant. It matters oh so very little from any point of
view.


Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

"W9DMK (Robert Lay)" skrev i en meddelelse
...
On Tue, 3 May 2005 18:41:17 +0200, ".J.S..."
wrote:

Building something a bit like this :
http://www.hamuniverse.com/multidipole.html

He suggests setting up one wire at a time starting with the longest, is
that
the easy way ?

I would think adding all wires, a bit too long , and then starting the
adjustment with the shortest would be better ?
All the other wires overlap the shortest 100%, so I would imagine later
trimming of longer wires i parallell would not affect the short wire much.

You are placing far too much importance on your objective of having
each dipole resonant. It matters oh so very little from any point of
view.


What would the purpose of building a multidipole be if not to get a
resonance on each band ?

My goal is to run psk31 on several bands without a tuner.




/JS

Hi:
There is a large amount of interaction between the dipoles as they are
tightly coupled to each other.
The shorter or higher frequency are affected more by changes to the lower
frequency i.e. longer dipoles than the lower frequency dipoles are by
changes to the higher frequency or shorter dipoles.
So to keep hair pulling to a minimum start with the lowest frequency dipole,
tune that for the lowest SWR or for resonance and then do the next lower
one. If you do it in any other order you will spend your life going back and
forth retuning dipoles until you give up and buy a G5RV kit and join the
dark side.


--
John Passaneau, W3JXP
Penn State University


".J.S..." wrote in message
. ..

"W9DMK (Robert Lay)" skrev i en meddelelse
...
On Tue, 3 May 2005 18:41:17 +0200, ".J.S..."
wrote:

Building something a bit like this :
http://www.hamuniverse.com/multidipole.html

He suggests setting up one wire at a time starting with the longest, is
that
the easy way ?

I would think adding all wires, a bit too long , and then starting the
adjustment with the shortest would be better ?
All the other wires overlap the shortest 100%, so I would imagine later
trimming of longer wires i parallell would not affect the short wire
much.

You are placing far too much importance on your objective of having
each dipole resonant. It matters oh so very little from any point of
view.


What would the purpose of building a multidipole be if not to get a
resonance on each band ?

My goal is to run psk31 on several bands without a tuner.




/JS

On Tue, 3 May 2005 20:52:37 +0200, ".J.S..."
wrote:

What would the purpose of building a multidipole be if not to get a
resonance on each band ?

Antenna pattern?

Danny

"John Passaneau" skrev i en meddelelse
...
Hi:
There is a large amount of interaction between the dipoles as they are
tightly coupled to each other.
The shorter or higher frequency are affected more by changes to the lower
frequency i.e. longer dipoles than the lower frequency dipoles are by
changes to the higher frequency or shorter dipoles.

Strange..
I can understand that hanging a long wire next to a short will affect more
than the other way round.

But if they are both up there, I would have thought trimming the long wire
would not change its affect on the short wire much.

So to keep hair pulling to a minimum start with the lowest frequency
dipole,
tune that for the lowest SWR or for resonance and then do the next lower
one.

Ok, thats the order of trimming, but do you install one wire at a time or
all of them at once ?




/JS

W9DMK wrote:


You are placing far too much importance on your objective of having
each dipole resonant. It matters oh so very little from any point of
view.

It's basically the whole point. No tuner needed, and a dipole
pattern for each band there is a dipole for.
Looking at that pix, they are using the "hard" to tune design.
The elements are close stacked, and this makes coupling a problem.
It would be much better to spread the dipoles out in different
directions, IE: N/S, E/W, etc, to keep them spread apart.
Always start with the lowest band and work up. If each dipole is
not resonant, how will you keep your radio from shutting down?
Use a tuner? That defeats the whole purpose, and the low loss of
of resonant dipoles, fed with coax. MK

".J.S..." wrote in message
. ..
Building something a bit like this :
http://www.hamuniverse.com/multidipole.html

He suggests setting up one wire at a time starting with the longest, is
that
the easy way ?

I would think adding all wires, a bit too long , and then starting the
adjustment with the shortest would be better ?
All the other wires overlap the shortest 100%, so I would imagine later
trimming of longer wires i parallell would not affect the short wire much.


It always bugs me that a length for 80 meters is given to a decimal point.
Also 119.2 feet seems way too short to put you in the packet area of 80
meters. I would think it would be closer to 130 feet or so. Maybe more.
Then you could cut it to length. I am not going to look up the lengths but
you may want to check the other dipoles to see if they are long enough for
the low end of the bands.

".J.S..." wrote in message
. ..

"John Passaneau" skrev i en meddelelse
...
Hi:
There is a large amount of interaction between the dipoles as they are
tightly coupled to each other.
The shorter or higher frequency are affected more by changes to the lower
frequency i.e. longer dipoles than the lower frequency dipoles are by
changes to the higher frequency or shorter dipoles.

Strange..
I can understand that hanging a long wire next to a short will affect more
than the other way round.

But if they are both up there, I would have thought trimming the long wire
would not change its affect on the short wire much.

So to keep hair pulling to a minimum start with the lowest frequency
dipole,
tune that for the lowest SWR or for resonance and then do the next lower
one.

Ok, thats the order of trimming, but do you install one wire at a time or
all of them at once ?




/JS

Yes put up all the wires at the same time. There will be an effect on the
lower frequency antennas by the higher frequency ones and putting up all the
wire will get you closer on the first try than putting them up one at time
and tuning them will. I've used this type of antenna for years and they work
quite well. The interaction between the dipoles can be minimized by putting
the dipoles at right angles to each other. That is say, run the 80m dipole
north/south and the 40m dipole east/west. That minimizes the coupling and
the dipoles act almost like single band antennas. In my system I have a
160/80/40/30 meter dipole antenna. It has the 80/40 wires running parallel,
spaced about 12" apart and at right angles to that is a loaded (shortened)
dipole for 160m and the loading coils in the 160m antenna act like traps and
make a 30m dipole. It's all feed with one coax.
The 80m dipole acts just about the same as if it was the only dipole up
there, but the 40m dipole is strongly affected by the 80m wire. The most
noticeable effect is the SWR bandwidth is a bit smaller than I would expect
from a single 40m dipole and the tuning is a bit more sensitive.By that I
mean it takes a smaller change in length of the 40m wire to move the
resonate point some KHz's than it would with a single band dipole. All that
means is you have to be careful with how much you cut off and take it in
baby steps, not big chunks. I first up the 80/40 antennas and a year later
I decided to get on 160 so I added the 160 wires. When I added the 160/30m
wires at right angles to the 80/40m ones there was almost no noticeable
effect on the 80/40m dipoles. You can download the EZNEC demo antenna
modeling program and see how the antennas interact your self. One thing you
will notice is that when your operating on 40m the 80m is also working a
little bit too. Anyway I have DXCC on 80 and 40 and working on it on 160 and
30m which are the last bands I need DXCC on.

Good luck


--
John Passaneau
State College Pa.

"John Passaneau" skrev i en meddelelse
...
So to keep hair pulling to a minimum start with the lowest frequency
dipole,
tune that for the lowest SWR or for resonance and then do the next lower
one.

Ok, thats the order of trimming, but do you install one wire at a time or
all of them at once ?



Yes put up all the wires at the same time. There will be an effect on the
lower frequency antennas by the higher frequency ones and putting up all
the wire will get you closer on the first try than putting them up one at
time and tuning them will. I've used this type of antenna for years and
they work quite well. The interaction between the dipoles can be minimized
by putting the dipoles at right angles to each other. That is say, run the
80m dipole north/south and the 40m dipole east/west. That minimizes the
coupling and the dipoles act almost like single band antennas.

In my system I have a 160/80/40/30 meter dipole antenna.

Thats exactly what I am trying make on top of a flat-roof building.
The building is 56x12 m so I cant quite get anything at a right angle but I
will try to get as much angle as possible. Also it is not long enough for
the 160m but the idea is to go diagonal and then across at the ends like a
'Z'.

It has the 80/40 wires running parallel,
spaced about 12" apart and at right angles to that is a loaded (shortened)
dipole for 160m and the loading coils in the 160m antenna act like traps
and make a 30m dipole. It's all feed with one coax.
The 80m dipole acts just about the same as if it was the only dipole up
there, but the 40m dipole is strongly affected by the 80m wire. The most
noticeable effect is the SWR bandwidth is a bit smaller than I would
expect from a single 40m dipole and the tuning is a bit more sensitive.By
that I mean it takes a smaller change in length of the 40m wire to move
the resonate point some KHz's than it would with a single band dipole. All
that means is you have to be careful with how much you cut off and take it
in baby steps, not big chunks. I first up the 80/40 antennas and a year
later I decided to get on 160 so I added the 160 wires. When I added the
160/30m wires at right angles to the 80/40m ones there was almost no
noticeable effect on the 80/40m dipoles. You can download the EZNEC demo
antenna modeling program and see how the antennas interact your self. One
thing you will notice is that when your operating on 40m the 80m is also
working a little bit too. Anyway I have DXCC on 80 and 40 and working on
it on 160 and 30m which are the last bands I need DXCC on.

Good luck

Thx and thx for the info



/JS