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Author Topic: Reflectors and Horizontal Wire Loop questions  (Read 7595 times)
WALTERB
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« on: May 10, 2013, 06:27:44 PM »



I have a couple of questions, and I’m hoping someone can help.
(1)    Does the Reflector of a Yagi only help during Receive or does it “Reflect” during Transmitting as well?

Has anybody tried putting up a Horizontal Wire Loop (Skywire) with a reflecting wire inside the driven wire?  (Delta inside a Delta) 
Or is that just a stupid idea?  :-)

thanks
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AC5UP
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« Reply #1 on: May 10, 2013, 06:41:02 PM »

(1)    Does the Reflector of a Yagi only help during Receive or does it “Reflect” during Transmitting as well?

The directional characteristics of a Yagi are the same for both TX and RX so reciprocity applies to the reflector and director elements...

Has anybody tried putting up a Horizontal Wire Loop (Skywire) with a reflecting wire inside the driven wire?

Work out the dimensions and you'll find there isn't enough room for a useful spacing in terms of wavelength. Nor would the internal reflector be anywhere near the size (or resonant frequency) of the driven loop. It's mechanically impractical.
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WALTERB
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« Reply #2 on: May 10, 2013, 06:50:36 PM »

thanks.

would making the inner delta wire driven be helpful?  I'm thinking something like a Fan Dipole, except a series of two delta loops, one inside the other.  I looked at the design of a HexBeam, and forgetting the "beam" part for now,  its a series of various length wires all connected to common feed point.  Could you do something similar with a delta loop, or yet another dumb idea?

(similar to this )
http://www.mds975.co.uk/Images/amateur_radio/sandpiper_gm3.jpg

thanks.
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AC5UP
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« Reply #3 on: May 10, 2013, 07:06:39 PM »

Do a web search on the words " cubical quad " and see what comes back.................  Wink
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WALTERB
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« Reply #4 on: May 10, 2013, 07:10:56 PM »

cool, thanks.
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WB6BYU
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« Reply #5 on: May 10, 2013, 07:19:36 PM »

Quote from: WALTERB

would making the inner delta wire driven be helpful...



It depends what you are trying to accomplish.  You can certainly build an antenna
like that, the question really is does it give any improvement in performance.  And
to answer that question you have to know what aspects of performance you want
to improve on.

On the band where the loop is full wave resonant, it won't add much.  That's
because maximum radiation is broadside to the loop (straight up if the loop
is horizontal) and the reflector isn't in the right place.  Not only that, but there
isn't room for a loop of the same size - or larger - to be placed inside the first
one.  If you want gain in one direction with such an antenna you would need
to turn it into something like a Moxon (or the forerunner VK2ABQ beam).  But
then it isn't a full wave loop, and won't work well on harmonics.

One reason the horizontal full wave loop is popular is because because the
radiation pattern moves more towards the plane of the loop on the harmonics:
for an 80m loop used on 20m or 40m there is a null overhead and more radiation
at the lower angles (useful for DX) than overhead.  In fact, the longer loop (2 or
4 wavelengths in this case) will have a better pattern for working DX than a full
wave horizontal loop at the same height.  That's why you don't often see
nested loops in the same way you see dipoles, except in multiband quads
where they use a separate set of elements for each band.  (There is also the
problem that, if you put a 80m loop and a 40m loop with the feedpoints in
parallel, the 80m loop will take a significant percentage of the power on 40m,
unlike the case with dipoles.)


You still can't add a reflector loop easily, but you could add a series of wire
reflectors tied end-to-end with lengths of rope and bent into a loop inside the
outer one.  By choosing how to position these you could probably get a bit of
gain in certain directions at  the expense of others.  There are a number of
other arrangements, but I don't think any of them will make a big difference.  
(Hmmm...  maybe if the inner loop had some folded stubs to reduce the
physical length while increasing the electrical length...)

One alternative is to add an identical loop below or above the first, to get
some broadside gain on those bands where the spacing is 1/2 wavelength or more.
This probably requires more height than many hams can accommodate with their
loops, since generally you don't get worthwhile gain by stacking two antennas
until the lower one is at least half the height of the upper one.  (Implying a
minimum height of about 60' to get useful gain on 20m, with the second loop
at half that height.)  Both loops would be fed in parallel in that case.


But the first step is to be clear about:
1) is this for operation on just one band or multiple bands?
2) are you concerned with gain in just one direction, or in all directions?
3) what other objectives are you trying to achieve?

You certainly can build such an antenna, the real question is whether there is
any benefit to doing so.
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WALTERB
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« Reply #6 on: May 10, 2013, 07:56:47 PM »

Wow, thanks so much for the response. this answers a lot of my questions.

Currently I have an OCF Dipole up at about 45 feet.  It works fine, but you know how it is, you are always looking for something a bit better without spending a lot more money. :-)

I have the location for the perfect horizontal delta loop at the same height (I was thinking a 40 meter, but there is room for an 80 meter).

I'll have to drop the OCF Dipole and cannibalize the support cords for it for the delta.

Most of my HF work is on DX 20 meters with the OCF.  I don't go on 40m or 80m much, but if a 2x or 4x wavelength would help my DX, then great!!!

I can also make the Delta closer to a square (more like a trapezoid)  if making the inner area of the loop large would help significantly?

I currently have this Balun on my OCF Dipole.
http://www.balundesigns.com/servlet/the-78/4-cln-1-dual-core-current/Detail
Can I use this on the Delta loop, or should I use a 1:1 choke or nothing at all?

thanks
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K8POS
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« Reply #7 on: May 10, 2013, 08:44:43 PM »

Answer your self this one question.
"What do you want your antenna to do?
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WALTERB
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« Reply #8 on: May 10, 2013, 08:54:34 PM »

Answer your self this one question.
"What do you want your antenna to do?

work better than the OCF Dipole I currently have in the same location. :-)
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K8POS
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« Reply #9 on: May 10, 2013, 09:30:37 PM »

I think you will find that any "Multi band single wire antenna is a compromise.  They will work great on a few bands and OK on others.  I went the same route as you are now going.  I ended up putting up a full size 80 meter horizontal loop  in a diamond configuration.   For me it gave me the all band (my TS-2000 can tune it 6-80 meters) that I wanted.  Works great on my favorite bands and very functional on the others.  It is not a beam, not the the best DXer, but gets me on all the bands and I have worked plenty of DX with it.  I do not have the funds, or the real estate to put up towers and multiple antennas.
You have partially answered the question.  Do you have trees to erect a loop with?  The picture you showed is kinda like a multi-band loop, AKA fan dipole in a loop set up.  Can be a real bear to get each loop tuned to the resonate frequency, let alone properly supported.  Which way is your OCF oriented?  The wire running North/South will be way different than if it is East/West.
As someone pointed out, a quad antenna for HF is huge, and directional, if you could properly erect it in a horizontal plane,  it would either be a good cloud burner or a ground pounder.  You may just want to play around the the orientation of the wire you have, it could make a great improvement, or make it worse.

Just remember, what ever you put up WILL WORK, how well depends on the band, design, mounting, and conditions.

Just my 2 cents
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WALTERB
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Posts: 528




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« Reply #10 on: May 10, 2013, 09:52:16 PM »

I think you will find that any "Multi band single wire antenna is a compromise.  They will work great on a few bands and OK on others.  I went the same route as you are now going.  I ended up putting up a full size 80 meter horizontal loop  in a diamond configuration.   For me it gave me the all band (my TS-2000 can tune it 6-80 meters) that I wanted.  Works great on my favorite bands and very functional on the others.  It is not a beam, not the the best DXer, but gets me on all the bands and I have worked plenty of DX with it.  I do not have the funds, or the real estate to put up towers and multiple antennas.
You have partially answered the question.  Do you have trees to erect a loop with?  The picture you showed is kinda like a multi-band loop, AKA fan dipole in a loop set up.  Can be a real bear to get each loop tuned to the resonate frequency, let alone properly supported.  Which way is your OCF oriented?  The wire running North/South will be way different than if it is East/West.
As someone pointed out, a quad antenna for HF is huge, and directional, if you could properly erect it in a horizontal plane,  it would either be a good cloud burner or a ground pounder.  You may just want to play around the the orientation of the wire you have, it could make a great improvement, or make it worse.

Just remember, what ever you put up WILL WORK, how well depends on the band, design, mounting, and conditions.

Just my 2 cents


thanks for the feedback. very interesting.

What are you feeding your loop with?  Ladder line? 600ohm Open Wire ladder line?  Coax?
my OCF dipole (Long end pointing due east, short end pointing south west.  An overhead view it would like like 5PM on a clock.  Not perfect, but normally on JT65 at 20 watts 5 continents can hear me. Actually I'm just finishing with a Japan station as I'm typing this.  I'm near St. Louis Missouri.

I would only be running the rig barefoot.
I have plenty of trees in the backyard to erect the sky-wire loop 80meters would be about the size limit.
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K8POS
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« Reply #11 on: May 10, 2013, 10:15:26 PM »

My loop is fed with 150' of 9913 coax, most of it underground, to a 4:1 balun, feed point is at 65', another at 30', and the third about 40'.  It is what I could best configure in my yard.  I want to take it down summer and try to double the length, just to see how much of a difference it makes.
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WALTERB
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« Reply #12 on: May 10, 2013, 10:23:39 PM »

My loop is fed with 150' of 9913 coax, most of it underground, to a 4:1 balun, feed point is at 65', another at 30', and the third about 40'.  It is what I could best configure in my yard.  I want to take it down summer and try to double the length, just to see how much of a difference it makes.

very cool!  thanks.
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WB6BYU
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« Reply #13 on: May 10, 2013, 11:15:56 PM »

Either a diamond or triangle loop of about 280' should give a low SWR on 20m
with a 4 : 1 balun at the feedpoint - probably good enough to cover the whole
20m band at under 2 : 1 SWR.  (Minor length adjustment may be needed to
center it in the 20m band, of course.)  Actual feedpoint impedance is around
250 ohms.  (If the 4 : 1 balun is too heavy to put at the feedpoint, then use a
balanced feedline that is a multiple of 1/2 wave to wherever you can mount
it, and you should still have a low enough SWR that you don't need a tuner. 
Note that this method narrows the SWR bandwidth.)

The pattern depends on the shape:  with a diamond the major lobes are off
the corners, with nulls in the directions of the sides.  The strongest lobe is
away from the feedpoint (assuming it is fed in one corner.)

With a triangle the strongest lobe is still away from the feedpoint, but there
are now 6 lobes rather than 4.  The nulls between them aren't as deep, so
it tends to be more omnidirectional, but the peak gain is about 2 dB down
from the diamond.

By contrast a 40m loop used on 20m still has a 4-lobbed pattern off the corners,
but broader lobes than the 80m loop and > 4dB less gain in the main lobe.

As long as you can aim the 4 lobes in useful directions, the 80m diamond will
probably give better performance for what you want.
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KE3WD
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« Reply #14 on: May 11, 2013, 06:26:25 AM »

Feeding your Delta Loop with Balanced Line and appropriate balun/tuner combination would likely yield improvement over coax feed in terms of being able to cover more bandwidth efficiently. 

Attempts at reflecting, while possible, would require a lot more space and also could eliminate signals that aren't in the direction of the reflections. 

A big horizontal loop w/balanced feed and tuner to match worked very well for me when I had the space.  I cut it long, to favor the CW portions of the 80 meter band, but found that using a big manual tuner (the old Heath bigbox at the time) allowed coverage from 80 on up to ten, to include the SSB portions of the bands. 

73
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