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Author Topic: Dipole choices - I thought I new what I wanted but.....  (Read 4804 times)
WB2WIK
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Posts: 20537




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« Reply #15 on: September 18, 2012, 01:50:21 PM »

I also want to thank everyone else that has respondedwith suggestions to try and help.

Any feedback on the so called"Mystery Antenna"


If you have to erect then take down an antenna frequently, the "Mystery Antenna" isn't a good choice: It's made from coaxial cable with splices in it and a lot of handling will likely damage it.

If you have a decent antenna tuner and use low-loss transmission line, the "limited bandwidth" of many designs isn't much of a problem.  It may mean having to re-tune more often, but if this is done in the shack where you're comfortable, it's not so bad and many thousands of hams do this every day.

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KF7NUA
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Posts: 153




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« Reply #16 on: September 18, 2012, 02:28:27 PM »

I have just been reading about a Doublet and it sounds like a good choice. There are a couple choices that I may be able to get up in the air, can they be mounted as a inverted V or is Horizontal manditory for them?

I found this one, it is a 88ft

My Top Five
Backyard Multi-Band Wire HF Antennas
L. B. Cebik, W4RNL
88ft version
88' 20, 30, 40, 60, 80 meters
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WB6BYU
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Posts: 12977




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« Reply #17 on: September 18, 2012, 03:48:16 PM »

It's a bit short for good efficiency on 80m, but otherwise OK.

The only magic about the 88' length is that it provides maximum radiation broadside
to the wire on 20m.  Any longer and the pattern starts breaking up into more lobes
and nulls (as the 88' length does above 20m.)

That's your trade-off:  longer lengths will be more efficient on 80m, while shorter ones
provide better broadside radiation on the higher ones.  If all the stations you want to
work are broadside to your antenna, then it makes sense to choose a length accordingly.
If stations are scattered in various directions, then having lobes and nulls scattered
around isn't necessarily a deficiency.

If 80m isn't as important, choose whatever length will fit and put it up.  You'll still
make contacts.
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KF7NUA
Member

Posts: 153




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« Reply #18 on: September 18, 2012, 04:00:35 PM »

I live in Southern Arizona, 40mi from Mexico, I only have one way to mount this, ends would be West to East +/-about 15deg, that is it.
I can also put a separate 20m dipole in a North to South or angled quite a lot if needed.

Any thoughts
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N8CMQ
Member

Posts: 353




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« Reply #19 on: September 18, 2012, 05:22:55 PM »

After a long learning experience on traps and loaded coils I have a question for the experts.
My needs are 20m and 40m but I would like to see what 75m and 80m is like.
I was just about to make separate 20m and 40m dipoles and then add additional loading coils on the 40m to also gain 75m or 80m too. I know that 75 or 80 will be very narrow bandwidth.
Question is:
Skip making the above 20m, 40m and added coils for 75m or 80m and just put up a 102ft G5RV.
My only problem is I will need to drop down the last 10ft or so on each end because I do not have the room.
Is this a better choice?
Will the G5 have better bandwidth?
I also think the G5 would be much cheaper to do.

thanks Nick


Hi Nick,
  Have you thought of a vertical trap antenna?
My 4 band vertical covers 10, 15, 20, and 40 meters edge to edge, CW to phone.
I have an 80 meter resonator that is tuned for the phone portion.
My vertical is ground mounted, and I have 125 radials 30+ feet long.
It was work, but it works!
BTW, no tuner...
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KF7NUA
Member

Posts: 153




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« Reply #20 on: September 19, 2012, 06:47:55 AM »

Yes I do have a vertical trap antenna, I have a R7 that will be going back up in a few weeks, I bought a tilt base and need to install it first. I had the R7 up until June when the Monsoon season hit this area. The R7 was the tallest thing around here next to the FM radio tower 1/4mi away and Lightning is always so intense that I decided to take it down for fear of a strike on it.
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KF7NUA
Member

Posts: 153




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« Reply #21 on: September 19, 2012, 06:54:37 AM »

On the doublet - where would I get one to purchase or the supplies to make one?
What supplies as in wire size or twinlead should I get?
I am hoping the smaller the wire the better for me.
I do have 2 Jackite 31' poles I could use to mount the wire as a horizontal as long as the weight of the wires is small enough.
These poles are so small at the top they will bend over with 14gauge and make them useless.
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KF7NUA
Member

Posts: 153




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« Reply #22 on: September 19, 2012, 07:10:57 AM »

So I want to get this correct.
My concerns are I want to have these bands for sure, 20m and 40m.
80m is an extra I do not have and would like to check out.
30m and 60m are just a bonus.

Easy to put up and down when I want to use.
I do have 2 different manual Tuners, I hope one of them is right for this, Palstar AT1KD and a MFJ941E.
Is there anything else I need?


I will most likely when I get time, which may never happen, make a 17m or a 15m dipole at another time!
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WB6BYU
Member

Posts: 12977




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« Reply #23 on: September 19, 2012, 08:09:00 AM »

One advantage of a doublet with a tuner is the same antenna works on all bands
40m through 10m, and possibly 80m to some extent if it is long enough.

Wire can be quite small actually.  I've used #24 or #26 for 80m dipoles where the
center was supported, and it is nearly invisible at a distance (even more so if you
use something with a matt finish so it isn't shiny.)  Once you get down to about
#32 the birds can't see it in time to avoid it, so you end up with more breaks.
Black stranded, insulated hookup wire may be a good choice - the common PVC
insulation will tend to crack after a year or two in the sun, but that would at least
give you an opportunity to get on the air and see how it works in the meantime. 
Besides, if you are taking it down all the time, replacing the wire wouldn't be a big
problem.  If you can't find something suitable, I have plenty out in the barn.

Choice of feedline depends on what is available and how much you have to hide it.
TV twinlead will work.  I've also made my own just using a pair of mostly parallel
wires stretched between two points.  You could, for example, use two lengths of
the same "invisible" wire spaced about a foot apart at the feedpoint (and perhaps
continuous lengths for each side of the doublet) running down to a point out of
view, with a commercial twinlead from there to the shack.  So, for example, you
could take two pieces of wire and measure about 40' or so in from each end.
Use a piece of black braided fishing line or similar cord to tie to each wire at
that point with about a foot or two of cord between them.  That becomes your
antenna.  The rest of the wire becomes your feedline.  At the bottom, tie off the
feedline wires 6" to 12" part, with enough tension so that, when the antenna is
installed, the wires don't flap around a lot.  Then connect regular commercial
twinlead to the bottom of the feed wires and run that into the shack.

That's just one of many ways you can do it with a minimum of weight and visual
impact.


Part of the problem with giving advice in an internet forum is that there are many
ways to do things, and there might be a perfect solution in your case that we
can't see.  The best we can do is to give you a number of options and let you
choose the one that seems the best fit. 
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KF7NUA
Member

Posts: 153




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« Reply #24 on: September 19, 2012, 08:58:13 AM »

Because I have a Vertical going up in the back yard also, what precautions will I need to make on the location of the Doublet and feed line in relation to where the Vertical will be installed?
Also does the Doublet twin lead need to be kept away from touching anything from the feed point to the tuner (this would be difficult I think)? Can it lie on the ground? I would also need to bring it into the home, I am thinking through a window that has a screen attached, will I need to buffer the lead from the metal window frame?
At any point should a 4:1un be used or just let the tuner handle it?
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KF7NUA
Member

Posts: 153




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« Reply #25 on: September 20, 2012, 08:29:10 AM »

Dale - I understand the concept of using a continuous wire as the feed line from the center point downward to a point where I connect a 300 line. What I do not know is does the vertical leg of the wire act as part of the antenna also which extends the length from 44’ per side to 74’ per side if the drop was 30’ long? The reason I ask this is because after reading many articles last night on the Doublet, I have realized that even though a length of 88’ will work, if I could just extend the length to around 100-110 it would be so much more efficient.
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WB6BYU
Member

Posts: 12977




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« Reply #26 on: September 20, 2012, 10:37:46 AM »

I was trying to give others an opportunity to comment rather than monopolizing the
conversation...

With the antenna wire running East/West, I think the longer (~100') wire would give you
a more useful radiation pattern on 20m.  The 88' will maximize radiation North/South:
there isn't much to the South of you, and, while you might get great satisfaction out of
working Idaho and Alberta, paths to India and Kazakhstan will be difficult due to passing
through the polar region.  The additional lobes of a 3/2 wave antenna should improve
performance into New Zealand, Africa, parts of Asia, and much of the Northeast US.

That's in addition to the improved efficiency on 80m.


Radiation from the feedline isn't a major problem.  As a rough guide, the radiation from
a balanced transmission line is about the same as that from a dipole with a length that
is the same as the width of the line, that carries the same current.  Even a 2' dipole
isn't going to radiate much, and the high impedance feed means lower current.  Besides,
if you are aren't trying to beam your signal to one specific location, feedline radiation
just contributes to the overall pattern.  So using wider spacing usually isn't a problem
on HF (especially if you keep the spacing below 0.1 wavelengths, which usually isn't
hard to do.)

I recommend the wider spacing at the feedpoint to reduce the chance of the feeder
wires getting twisted around each other.  That doesn't stop the antenna or the feedline
from working, but it will change the characteristic impedance and cause the SWR to
vary when it is windy.  That can be annoying.  By using wider spacing and a bit of tension
on the wires they should be better behaved.

Two parallel wires with a balanced load and fed out of phase will act as a transmission
line regardless of whether there is a splice at the feedpoint, or whether the wires were
sold for that purpose originally.

So, in this case, the feedline doesn't extend the antenna from the perspective of the
radiation patterns.  It does affect the impedance seen at the tuner, of course, just
as any feedline would.


Routing balanced line to the shack requires a bit more care than coax.  Because the
electric field extends beyond the wires (by a few times the wire spacing) you don't
want to lay it on the ground or other conductive or lossy surface.  Crossing metal
objects isn't too bad, as long as you try to keep the feedline wires equidistant from
it to avoid imbalance.  I had one feedline that came in through the holes in a vent
screen in the attic (which may require some additional insulation slipped over the
wire at that point) and through the attic until it spliced into a piece of TV twinlead
that dropped down through the ceiling to the shack.  6" to 12" spacing away from
metal or lossy objects is usually adequate.  I think I still have some of the old
stand-off insulators sold for 300 ohm TV twinlead, but you can usually improvise
something for the larger lines.  (Running it along a fence is often convenient.)

While it is often good to space antennas reasonably far apart, it won't be the
end of the world if one end of your wire antenna comes within 5' of your vertical:
coupling will be relatively low because they will be cross-polarized.  You do what
you can manage.

Send me an email (my call at a-double-r-l dot net) with your address and I'll
build an antenna and send it to you.
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W9GB
Member

Posts: 2579




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« Reply #27 on: September 20, 2012, 11:18:53 AM »

Quote from: kf7nua
I bought a tilt base and need to install it first. I had the R7 up until June when the Monsoon season hit this area.
The Cushcraft R7 was the tallest thing around here next to the FM radio tower 1/4mi away.
Lightning is always so intense that I decided to take it down for fear of a strike on it.
DOUBLE CHECK, that you have a GOOD RFC1 in the black matching box, MN7 of your R-7 vertical.

RFC1 is there to drain atmospheric static charges from the vertical element.  
Radio Spares (UK), part number, 213-1932, 470uH, 0.3A (costs just under one UK pound).

Nearby Lightning strikes have been known to OPEN (no static drain function, but R-7 usuable) or SHORT (R-7 not functional, high SWR) RFC1.
http://www.iol.ie/~bravo/r7_vertical.htm

==
w9gb
« Last Edit: September 20, 2012, 11:23:46 AM by W9GB » Logged
KF7NUA
Member

Posts: 153




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« Reply #28 on: September 21, 2012, 06:41:16 AM »

Quote from: kf7nua
I bought a tilt base and need to install it first. I had the R7 up until June when the Monsoon season hit this area.
The Cushcraft R7 was the tallest thing around here next to the FM radio tower 1/4mi away.
Lightning is always so intense that I decided to take it down for fear of a strike on it.
DOUBLE CHECK, that you have a GOOD RFC1 in the black matching box, MN7 of your R-7 vertical.

RFC1 is there to drain atmospheric static charges from the vertical element.  
Radio Spares (UK), part number, 213-1932, 470uH, 0.3A (costs just under one UK pound).

Nearby Lightning strikes have been known to OPEN (no static drain function, but R-7 usuable) or SHORT (R-7 not functional, high SWR) RFC1.
http://www.iol.ie/~bravo/r7_vertical.htm

==
w9gb

Thank you for the link  Grin
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AE5JU
Member

Posts: 223




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« Reply #29 on: September 22, 2012, 09:54:08 PM »

My previous suggestion was to add the 80m loading coils and extension wires to
the 20m wires rather than the 40m wires.  You can then get all three bands in
the same space as a 40m dipole.

Here is an example (though you don't need to follow all the details):

http://www.hamuniverse.com/ae5jufielddayantenna.html

I was just about to mention that...  ;- )

BTW, Field Day before last, we made contacts from here on the Louisiana Gulf Coast from NY to San Diego, CA with two of these antennas, on 20 and 15 meters with 50 w SSB from a Ten-Tec Scout, and FL, GA, SC, FL, AL, MS, OK, TX on 40 m with 100 w SSB from an Icom 718.  Also have checked in on LA and TX nets on 75 m operating from a nearby school yard with the 718 and 100 w SSB, using batteries.

The 75 m / 20 m portion is about the same span as the 40 / 15 meter portion.

Paul - AE5JU
« Last Edit: September 22, 2012, 10:04:19 PM by AE5JU » Logged
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