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Author Topic: What would you do with 215' at 70 feet?  (Read 2649 times)
KJ4RQV
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Posts: 130




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« on: March 31, 2013, 04:15:00 PM »

I like fooling with wire antennas and have a space that I would like to fill. In front of my house are two trees just begging to have an antenna hung from them. I could easily hang a wire at about 70-80 feet high and it could be up to 215-20' long.

If it were a dipole I even have a 25' tall  pine at the center point that could be used to stabilize a ladder line feed/balun with coax going to the shack. The coax would have to be somewhere around 150' long and I don't know if that would cause a RF problem at the radio.

I usually work QRP SSB with a K2 Elecraft though sometimes I light up the Kenwood TS520 and go up to 80-100 watts.

I'm open to opinions and suggestions as to something besides a CFD. I just hate to waste those trees and that space.
Don
« Last Edit: March 31, 2013, 04:17:59 PM by KJ4RQV » Logged
WB6BYU
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Posts: 13243




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« Reply #1 on: March 31, 2013, 05:07:40 PM »

What distances are you interested?  What bands?

How are the trees aligned relative to useful directions?

For local work on 80m you could put up a shortened colinear array.  For DX you could
use a Sterba curtain broadside to the trees or a delta loop hanging from a rope
between the trees in line with them.  For 80m DX you could rig up a Bobtail Curtain.

There are lots of options - first you have to decide what result you want to achieve,
then design an antenna accordingly.
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KJ4RQV
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Posts: 130




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« Reply #2 on: March 31, 2013, 05:18:57 PM »

I use a NVIS for local on 80 and 40.

A hanging delta loop probably is out because a farm road lies under the path of the antenna.

I had not considered a Sterba curtain so I must get my antenna book out to look at that.

The antenna would stretch from WSW to ENE. I will most like to work the western NA continent and work on 40, 20, 17  and 15 meters. I like to rag chew with people about their lives and am not so much into nets or contests.

My current antenna is a dipole at about 50-60 feet, cut for 80 meters in different trees and it runs S-N. It is great for South America and East coast stations. I am working some European stations with it also. I think it is working well and tunes well but I just want to try something else.
« Last Edit: March 31, 2013, 05:40:16 PM by KJ4RQV » Logged
KC4MOP
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Posts: 733




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« Reply #3 on: April 02, 2013, 08:41:04 AM »

The two tall trees are begging for a dipole. 70-80 feet high and 240 feet of dipole and open ladder line and look out!! The ends of the dipole can drape down at the ends and not harm anything. Antenna good for 160-40M. 80M will start to become directional.  40 definitely. 20 would be ok just some pattern distortion from being too high.
Hopefully the trees would be in a favorable direction or, because this is a hobby, stick one up and have at it.
You would need a nice antenna tuner for balanced line. Open Wire line. The OLD FASHIONED type with 6 inch spacing between wires (600ohm). Window line (450ohm) isn't stable when wet.
Here's a company that sells ladder line and antenna. One continuous length of wire. You can look at what they are doing and make your own. Buy the wire from them and make your own spacers. Their wire is very nice to work with. Or buy very flexible antenna wire from: The WireMan

http://www.thewireman.com/products.html

The Ladderline/Antenna folks:
http://www.trueladderline.com/

Geday
Fred
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K0CWO
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Posts: 418




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« Reply #4 on: April 02, 2013, 09:11:06 AM »

I second kc4mop.  I had a (http://www.trueladderline.com/) 260 foot flat top dipole 100 feet above the ground, no center support, fed with 175 feet of 600 ohm open wire line fed into the shack to a Ten Tec 238B tuner and an Al-80B amplifier.  The antenna was oriented E-W.  I was in Kansas at the time and on 160 and 80 it was an "easy" coast to coast antenna.  I even worked a bunch of SSB DX on those bands.  On 40 and up it was a barn burner.  I am not a "worked all" anything person so the directionality on those bands I really didn't notice because I worked anyone I could hear world wide.  I wish I could replicate that antenna in my current situation.  Best casual all band antenna I ever used!  I would not worry about 20 feet of flat top hanging down on each end if you choose to go this route.  I bet you wouldn't notice a difference between a flat top and a flat top with the ends hanging down given your dimensions.   

73, BJ
k0cwo 
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WB6BYU
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Posts: 13243




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« Reply #5 on: April 02, 2013, 12:40:57 PM »

Well, let's see what we can do...

The first stop is NS6T's Azimuth map page here: 

http://ns6t.net/azimuth/azimuth.html

It doesn't recognize Kelso, but entering "Fayetteville, TN" is probably
close enough for this purpose.  A distance of 4000km is a good starting
point.

That gives you a sense of what directions will be useful for radiation.

Due West (270 degrees) puts you straight through Arizona and New Mexico,
and just South of the bottom of California.  Also includes Hawaii (about 275
to 280 degrees.)  Meanwhile 310 degrees puts you through Montana and
Vancouver, BC, while 330 degrees gives better coverage of
the Dakotas, Saskatchewan, Alberta, and much of Alaska.  So a beamwidth
of 40 to 60 degrees should cover most of what you want:  any sharper and
you'll either cover a smaller portion of the area or need to rotate it the pattern.

Distances range from 1000km (Kansas, Oklahoma, Iowa), 2000km (Wyoming
and the 4-corner states) and 3000km (California, Oregon, Washington.)  That
gives you an idea of what vertical radiation angles are going to be best.  Most
of Alaska is in the 4000 - 6000km range, and Hawaii is 7000km.

Approximate vertical angles for various distances:

1000 miles requires 12 to 22 degrees (about the edge of Colorado).
2000 miles requires 0 to 8 degrees (about the West Coast)

Longer distances typically require multi-hop propagation or other modes,
but generally radiation angles below 20 degrees.  The vertical radiation
pattern from a horizontal antenna up 1 wavelength is maximum at about
15 degrees, with a null at 30 degrees, so you're at a good height.


Now, a wire running WSW to ENE puts it about at 68 / 248 degrees.  So
the requires shift from the direction of the wire is about 20 to 80 degrees.
The radiation pattern of a wire antenna 1 wavelength or more splits into
lobes and nulls, and, as you increase the length in wavelengths (by operating
at a higher frequency) the maximum will tend closer to the direction of the
antenna.  This is a very promising development: an end-fed full wave wire
has a maximum about 40 degrees from the direction of the wire, so an
antenna with two full wave sections fed in the center (or an 80m dipole
operated on 20m) will have a maximum through Colorado, Utah, Nevada,
and northern California.  The same antenna on 10m would have a maximum
at about 25 degrees to the wire,  pointing at Los Angeles and Hawaii.
On 40m such an antenna would point broadside, giving coverage of the
Dakotas and Canada.

Note that the lobes aren't pencil-thin beams - they have a beamwidth of
several tens of degrees, so you'll work stations well on either side of the
maximum direction.  But it does give you an idea of just where it is
pointed.

While you nearly have room for a 160m doublet, you may find that the
directional patterns are aimed too far to the South (except on 40m, where
it would be similar to the 80m dipole used on 20m described above.) The
simple 80m doublet probably gives a better azimuth pattern on most bands
relative to your areas of interest.  But if you want to be creative and try
something new you could put up two such antennas end-to-end (or use
shorter doublets to fit the space.)  With two of them using identical lengths
of feedline you can switch the phase at the feedpoint to make them in
phase or out of phase, which will shift the lobes and nulls in the pattern.
I'd need to run some simulations to confirm the patterns, but that would
give you more flexibility using the same amount of wire, with just the
addition of more ladder line and a reversing switch.
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KJ4RQV
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Posts: 130




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« Reply #6 on: April 03, 2013, 12:34:38 PM »

WOW!

How do you know all that stuff?!? I can see that I just need to get an antenna up between those trees and see what it will do. i need to build a true open wire feed line and get going.
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WB6BYU
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Posts: 13243




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« Reply #7 on: April 03, 2013, 01:02:52 PM »

Quote from: KJ4RQV

How do you know all that stuff?!...




I went through a similar analysis and presented it to our club for Field Day last
year.  From here in Oregon we just point our antennas due East, but several
members were putting up multiband antennas (OCFD, G5RV, etc.) that radiated
mostly in other directions when installed broadside.  In most cases a simple
dipole would do better.

NS6T's azimuth map was a Godsend, as I could plot radiation patterns on top of
it to show the relative coverage in various directions.  Data on vertical angles
vs. distance were pulled from various reference books and articles (they can be
calculated based on the height of the ionosphere).  The antenna patterns for
doublets of various lengths are available in a number of books and web sites,
and are simple to generate with any antenna modeling software.

In my case, I happened to have a copy of my PowerPoint presentation handy
and pulled it up to check the radiation angles of the antennas, etc.  I had run
the models in EZNEC for various bands, and overlayed the plots for the different
antennas on a background of the NS6T azimuth map centered on our Field Day
site.

This important thing in your case is to look at the desired directions from your
location, and their relative angle compared to the antenna you propose to put up.
Anyone can do this analysis - the data are available somewhere for almost any
antenna type if you don't want to do your own modeling.  Ideally you want to
consider both the horizontal and vertical angles required for any specific path,
because the pattern of many antennas will show maxima in different directions
as you change the elevation angle.

What made this case particularly interesting was that the desired directions are
neither broadside nor inline to the direction of the antenna, and the lobes in those
directions vary with frequency.  With long straight wires (long in terms of wavelength)
there are many lobes and nulls, and sometimes it is difficult to keep them aligned in
the desired direction as you change bands.


Oh, and don't be too worried about using "True Ladder Line":  it won't give you
a significant improvement over several other options.  Use whatever you have
available.  (Sometimes you may specifically want to use different wire materials,
such as Copperweld(R) for the horizontal section and solid copper for the
transmission line.)  As long as you provide sufficient stress relief at the feedpoint
it shouldn't make any difference whether the antenna and feedline are constructed
of a single continuous piece of wire or not.
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KC4MOP
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Posts: 733




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« Reply #8 on: April 04, 2013, 01:56:50 PM »

The True Ladder Line link was a reference to show the OP how to string something pretty basic and simple quickly. If he is really serious about chasing DX, then the direction of the antenna becomes important. A dipole needs to be either 1/4 or 1/2 wave above ground before a direction is noticed.
Beverage antennas used as auxiliary RX antennas are needed to get into the serious DX.
My thought of a True Ladder Line approach can be done at home. Youtube has some good vids how to construct ladder line. All that's needed is a balanced tuner. And you have multiband operation. What I liked about the continuous wire with no splices, is to reduce the possibility of bad solder joints.
I was plagued with bad solder joints many times with previous antennas. I haven't had to pull my present dipole down for any connection issues for 3 years. It is a challenge to get a nice solder joint working outside in cold WX. The soldering gun (electric) never seems big enough to over come the cold and make a nice flow of solder. And Mother Nature wrecks your typical solder connection over time. Silver solder is a lot better in the elements, now you need a hotter iron/flame to melt silver solder.
Using a blowtorch (MAPP gas), really makes an ugly solder joint and burns the insulation. That was my problem on many dipoles in the past. Any soldering outside takes a lot of extra precautions.
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W4VR
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« Reply #9 on: April 05, 2013, 12:51:49 PM »

With a span that long between the two ends you would end up with very significant droop at the center of the antenna if that's where you feed it with your transmission line.  Anything longer than 100 feet I use a center support to get away from the droop problem.  Also, you have to consider the tree sway, so you really can't pull the wire too tight...the supporting ropes or wire will stretch and break under high wind conditions.  I once used a center-fed wire 178 feet long (extended double zepp for 40 meters) and fed it with 90 feet of window line; it worked great on all bands, including 160 meters.  I used 90 feet of window line to avoid getting a voltage max on the transmit end.
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KC4MOP
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Posts: 733




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« Reply #10 on: April 06, 2013, 04:49:05 AM »

I agree with span and droop. It's not that bad. I have 240 feet of wire up 65 feet. One end is on the very top of a pine tree and the other is on my 70 foot utility pole. High winds make a lot of movement, and when the WX settles down I will add a marine type pulley on the pine tree end and whatever weight is needed to keep reasonable tension on the antenna without excessive pulling.
I used WireMan antenna wire that has many many strands and very flexible.
My setup has been up for 3 years and survived 60 mph winds and a close call with a twisting type wind that was almost a tornado. My wx station recorded gusts near 90 mph. I thought it was a gonner, but still standing.
The continuous wire design that is the ladder line held together with black flexible PVC, and then becomes the antenna is not that bad of a wind load. The ladder line that leads to the shack is 175 feet long. My Dentron 3KA tuner is very happy from 160M - 15M. I use my Yagi for 20M and up.
Fred
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W5LZ
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Posts: 477




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« Reply #11 on: April 13, 2013, 10:38:01 PM »

What would I do with 215 feet at 70 feet?  I don't know, but I'd sure love to try it!  Can't predict how it would work on most bands but I'd bet I could make it work better than most antennas I've ever had.  Add a few feet (as already suggested) to make it a 1/2 wave on 160 and I think I could have a ball with it.  I think I'd center feed it with ladder-line through a tuner (also suggested), and 'make do' with whatever it does.
 - Paul
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KC4MOP
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Posts: 733




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« Reply #12 on: April 14, 2013, 04:07:50 AM »

The multi-band dipole I have been commenting about is almost 65 feet high and same length.
It is a fair DX antenna on 160M. An inverted "L" is much better for DX.
on 80-20 I have had very good success with very good DX. I wasn't concerned about what direction it was pointing. I just threw it up.
It is fed by 150 feet of OWL to a nice Dentron 3KA balanced tuner.

Fred
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N6AJR
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« Reply #13 on: April 15, 2013, 12:10:15 PM »

a fan dipole, or a big loop.
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NR4C
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Posts: 308




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« Reply #14 on: April 16, 2013, 11:17:08 AM »

"Get it up!"
"Hook it up!"
and
"Light it up!"

have fun...

...bill  nr4c
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