Multi-band dipole question
 

Hello,

Just joined the group and I have a question about constructing a multi-
band dipole.

I plan to construct a 80/40/20/15 band multi-element dipole using
separate dipole wires for each band,
but a single feedpoint. My question is: how important is the spacing
BETWEEN the
individual band wires. I understand that they can't/shouldn't touch,
but is there any distance
that is optimal? or is just keeping them from touching enough?

Thanks,

Mike
KD7VRG

Multi-band dipole question
 

On 19 Apr 2007 12:17:00 -0700, wrote:

Hello,

Just joined the group and I have a question about constructing a multi-
band dipole.

I plan to construct a 80/40/20/15 band multi-element dipole using
separate dipole wires for each band,
but a single feedpoint. My question is: how important is the spacing
BETWEEN the
individual band wires. I understand that they can't/shouldn't touch,
but is there any distance
that is optimal? or is just keeping them from touching enough?

Thanks,

Mike
KD7VRG

I have used those antennas most of my life. I call mine a
parallel-fan dipole. I usually use 4" spacing for convenience. I use
PVC pipes with holes drilled in them the same diameter of the wire for
spacers.
However, there is a little secret to the parallel-fan. If the spacing
is pretty close to 8 inches apart, then you can setup the 75/80 meter
element and reverse engineer the length to the frequency. THen
substitute the new formula for the 468/f formula and you won't do so
much trimming on the other elements.

The advantage to the 4" spacing is that on 80 & 40 meters, you get a
broader bandwidth.

I really don't know of any better dipole arrangement when there is
room enough for this one.

Buck
N4PGW

--
73 for now
Buck, N4PGW
www.lumpuckeroo.com

Multi-band dipole question
 

Multi-band dipole question
 

Wow! Thanks for so many replies so quickly. I think I will go with a
"fan" design rather than parallel.
Another question though. What balun should I use? 1:1? 2:1? 4:1?
How do I know which?
Or can I just do the "coil the coax" thing...?

Thanks

Mike
KD7VRG

Multi-band dipole question
 

Multi-band dipole question
 

So would a 80/40/20 be the thing to make? For whats it's worth, I
don't have a tuner right now.
I just want to cut each for the middle of the band for General phone,
and accept whatever bandwidth
I get.

Mike
KD7VRG

Multi-band dipole question
 

You won't need much of an impedance transformation, so a 1:1 "current"
balun (common mode choke) is appropriate. A coil of coax makes a broadly
resonant circuit for currents on the outside, so acts as a current balun
over a fairly wide range of frequencies. My experiments show a
reasonable impedance over about a 3:1 or so frequency range. To be
effective over a wider bandwidth, you'll need a couple of different
sized coils, or a balun using ferrite, which is inherently broad banded.

Roy Lewallen, W7EL

wrote:
Wow! Thanks for so many replies so quickly. I think I will go with a
"fan" design rather than parallel.
Another question though. What balun should I use? 1:1? 2:1? 4:1?
How do I know which?
Or can I just do the "coil the coax" thing...?

Thanks

Mike
KD7VRG

Multi-band dipole question
 

Multi-band dipole question
 

I use a fan type dipole. The wires are 66' 33' and 16' each side so double
that for total length. (befor I tuned them but thats close) with an air
wound choke at the feed point.
Fan is not exactly right for my antenna ...here is what I did...

I used pvc as a spacer between each wire, the first spacer is 12 inches
from the feed point (I wanted to get the wires apart from each other as
close to the feed point as possible to minimise interaction between them)

They are separated 12 inches apart over the whole length and hang under
each other, the longest being on top.
The top wire (the 66') is the one that has rope connected to it (via
insulator) to tie the ends of the dipole to whatever. in my case, It is an
inverted V so I used 2 20' poles to anchor the ends of the dipole to.

Since the ends of the 33 and the 16 footer were just hanging from the pvc
spacers attached to the 66 footer, I placed a weight at the ends of them to
keep it all from twisting up in high winds.

I also ran a line from the ends of the 33 footer down to my poles (a few
feet below where the ends of the 66 is tied off, for the same reason. ( I
find that weed eater string holds up really well for this and it is cheap)

I can use it on all bands from 10 to 80 meters and even right around 1.8
mhz on 160 with a cheap mfj tuner. (not sure why it will work at 1.8 mhz, I
never worked out the math)

I get great signal reports with it on my ts-440s (bare bone at 100 watts)
and as a general rule, if I can hear them, I can work them.
"Roy Lewallen" wrote in message
...
wrote:
So would a 80/40/20 be the thing to make? For whats it's worth, I
don't have a tuner right now.
I just want to cut each for the middle of the band for General phone,
and accept whatever bandwidth
I get.

That'll get you on those three bands and, as I mentioned, you can
probably get a reasonable impedance on 15 as well by fiddling the 40
meter antenna a bit. It won't be quite resonant on 40, but probably
close enough so your rig won't shut down.

Roy Lewallen, W7EL

Multi-band dipole question
 

On 19 Apr 2007 12:17:00 -0700, wrote:

Hello,

Just joined the group and I have a question about constructing a multi-
band dipole.

I plan to construct a 80/40/20/15 band multi-element dipole using
separate dipole wires for each band,
but a single feedpoint. My question is: how important is the spacing
BETWEEN the
individual band wires. I understand that they can't/shouldn't touch,
but is there any distance
that is optimal? or is just keeping them from touching enough?

Thanks,

Mike
KD7VRG
There is a picture in most ARRL antenna books that shows a fan dipole
made from twin lead that just don't work!

Other than that, my experience with fans has been good. They are easy
to adapt to any environment. The same tactics adapt to a vertical
quarter wave as well.

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

Multi-band dipole question
 

On Apr 19, 4:28 pm, Roy Lewallen wrote:
wrote:
So would a 80/40/20 be the thing to make? For whats it's worth, I
don't have a tuner right now.
I just want to cut each for the middle of the band for General phone,
and accept whatever bandwidth
I get.

That'll get you on those three bands and, as I mentioned, you can
probably get a reasonable impedance on 15 as well by fiddling the 40
meter antenna a bit. It won't be quite resonant on 40, but probably
close enough so your rig won't shut down.

Roy Lewallen, W7EL


He may notice a resonant point around 27-28-29 mhz also..
If you use a length a coax to feed, that will add a 1/4 wave
of length to the 80 legs, IE: about 60-70 feet, you can feed
the shorted coax end from the shack, and run it on 160m as
a vertical. When I use the 40 legs for 15m, I usually slap a
tuner inline as a line flattener to keep the radio happy, and
also increase the usable bandwidth. I usually don't trim the
40 antenna to get a match on 15, as I prefer the 40 legs to
be tuned where I cut it, which is usually in the middle of the
band, so I can work both phone and CW. Any cheap tuner
will easily give a good match for 15m, and the loss is going
to be low, being the match isn't bad to begin with.
In the old days with tube rigs, I never worried about tuning 15.
The rigs would tune it no problem, with no tuner required.
But the newer solid state radios are a bit pickier.. So I'll
put the tuner on. I have a 989c which is always inline, but
rarely actually used in most cases, except for the meter,
and in rare cases like 15m, 30m, and maybe 160m where
I want to tweak the match a bit.
MK

Multi-band dipole question
 

John Ferrell wrote:
On 19 Apr 2007 12:17:00 -0700, wrote:


Hello,

Just joined the group and I have a question about constructing a multi-
band dipole.

I plan to construct a 80/40/20/15 band multi-element dipole using
separate dipole wires for each band,
but a single feedpoint. My question is: how important is the spacing
BETWEEN the
individual band wires. I understand that they can't/shouldn't touch,
but is there any distance
that is optimal? or is just keeping them from touching enough?

Thanks,

Mike
KD7VRG

There is a picture in most ARRL antenna books that shows a fan dipole
made from twin lead that just don't work!

Other than that, my experience with fans has been good. They are easy
to adapt to any environment. The same tactics adapt to a vertical
quarter wave as well.

I find that trying to prune/tune a multiwire antenna (like a fan) is an
exercise in frustration because of the strong interactions among the
elements, aggravated by the fact that most people install antennas in
places other than a vacuum. there's wind blowing (which changes the
spacing), trees, other stuff, etc.

So, I figure that if you get it "reasonably close", and then use an
autotuner to deal with the rest. If you want to obssess about loss in
the feedline, then put the tuner at the feedpoint.

Yes, the tuner costs some money, but it's a one time investment, and
makes playing with wire antennas much more pleasant and fast. Once
you've got that tuner, you can literally build decent antennas in 10
minutes with parts from the grocery store.

If you get a tuner that has a computer interface, then you can use it to
measure the Z of the antenna, if you feel compelled to prune.

Multi-band dipole question
 

On Apr 20, 12:16 pm, Jim Lux wrote:


I find that trying to prune/tune a multiwire antenna (like a fan) is an
exercise in frustration because of the strong interactions among the
elements, aggravated by the fact that most people install antennas in
places other than a vacuum. there's wind blowing (which changes the
spacing), trees, other stuff, etc.

Thats why I always spread them apart. I never stack the elements,
or have them closely spaced. I'll place them at right angles,
if only two bands.. The third band, I'll usually stick equally
between the others. If you have a coupling problem with
the third band, often just moving that leg a few feet one
way or the other will cure the problem. Once you do that,
you won't have wind problems with the higher band.
The only other type "all band" dipole I use is the "sectioned"
dipole, where you use insulators, and clips to open/short the
overall length of the dipole for other bands. But I only use those
when camping when I can only string a single wire.


So, I figure that if you get it "reasonably close", and then use an
autotuner to deal with the rest. If you want to obssess about loss in
the feedline, then put the tuner at the feedpoint.

Most of the time the loss is not a big deal. Only on the "hi Z"
bands,
where the antenna is a full wave, etc, will it be a problem. And even
then, you can still operate. I use 213 coax, so if the SWR is under
say 5:1, and I'm on a fairly low frequency, the loss is not a big
deal.
That's about my scenario on 30m, where I have no resonant elements.
Still works quite well.

Yes, the tuner costs some money, but it's a one time investment, and
makes playing with wire antennas much more pleasant and fast. Once
you've got that tuner, you can literally build decent antennas in 10
minutes with parts from the grocery store.

Maybe so, but I can do the same without a tuner too...
I don't use a tuner on the normal "resonant" bands.
A coax fed dipole is my favorite 10 min "quicky" antenna.
The only cost is coax and a bit of wire. No tuner
needed, and the system efficiency is hard to beat.
My 989c will handle open wire feeders, but I don't use them much.

If you get a tuner that has a computer interface, then you can use it to
measure the Z of the antenna, if you feel compelled to prune.

Actually, I can probably do it faster from sense of smell... :/
I find the same thing using the analysers... I can often tune
an antenna faster the old fashioned way, then using the new
fangled analysers.. I don't own an analyser myself, but I
have tried the MFJ versions that friends of mine have.
I'm too cheap to buy one, thats for sure... All it does is
verify what I can already see using the old methods.. :/
MK

Multi-band dipole question
 

The trick I have found..

Is to space the wires 12 inches apart, as close to the feed point as
possible.
With my antenna, it goes from the feed point to a 12 inch separation 18
inches from the feed point.
The wires are 12 inches apart from that point on and there is very little
interaction between the wires if any. At least my antenna analyzer cant find
any.

Like I said, the trick is to move the wires away from each other as close
to the feed point as possible.
I have found with this set up, that wind etc. changes very little.

Like I have stated before, my wires are hung under each other, so I have no
idea if the same concept would work with a true fan dipole....



I find that trying to prune/tune a multiwire antenna (like a fan) is an
exercise in frustration because of the strong interactions among the
elements, aggravated by the fact that most people install antennas in
places other than a vacuum. there's wind blowing (which changes the
spacing), trees, other stuff, etc.