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Author Topic: A 40 meter acute angled inverted Vee Log periodic antenna question.  (Read 2850 times)
WA2TPU
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Posts: 218




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« on: December 31, 2012, 04:28:11 PM »

1st off...A Healthy, Happy, and SAFE 2013 to all my ham Brothers and Sisters.

Well....its antenna hanging time here in Upstate NY....It was a balmy 14 degrees this morning with nearly 2 1/2 feet of snow on the ground. No, I don't put the antennas up anymore...My only son does. He actually likes putting them up in the Winter months because he can see where they're going- no leaves.
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WA2TPU
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Posts: 218




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« Reply #1 on: December 31, 2012, 04:44:32 PM »

1st off...A Healthy, Happy, and SAFE 2013 to all my ham Brothers and Sisters.

Well....its antenna hanging time here in Upstate NY....It was a balmy 14 degrees this morning with nearly 2 1/2 feet of snow on the ground. No, I don't put the antennas up anymore...My only son does. He actually likes putting them up in the Winter months because he can see where they're going- no leaves.
 The question I have for those who might know the answer is...I built a 4 element mono band 40 meter log periodic that is about 70 feet long taken from the April 1980 Ham Radio magazine. Where I'm going to have my son install this antenna is a swath about 20 feet wide and 100 feet long more or less and up about 35 feet constant height strung on a rope or wire between 2 trees.
My question is since the inverted Vee elements are going to have about 20 ...maybe 25 degrees angle to the ground...will this log periodic antenna be vertically polarized? Should I also slope these elements ahead since they'll be about 30 feet extra left in this swath or should the elements be straight down from the rope/wire the antenna's hung on. Also any thoughts on possible radiation pattern of this antenna? It will be pointing towards ZS land. Thanks for your thoughts.
Best regards and many 72/73.
Don sr. --WA2TPU --
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WB6BYU
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Posts: 13461




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« Reply #2 on: December 31, 2012, 04:58:26 PM »

Quote from: WA2TPU

My question is since the inverted Vee elements are going to have about 20 ...maybe 25 degrees angle to the ground...will this log periodic antenna be vertically polarized?



Do you really mean 20 degrees to the ground, or 20 degrees to vertical?

20 degrees to the ground is close to flat, and should work well.  It will mean
that the wires extend well beyond the 20' cleared path, however.

20 degrees to vertical is a very steep angle.  Not only is that going to mess
up the feedpoint impedance of the Log Periodic, but it won't be very efficient,
either, because much of the radiation from one side of the dipole will be
cancelled out by that from the other side.  I think it is unlikely to work well.

No, that doesn't make it vertically polarized.  Both wires will have horizontal
and vertical components.  If you look at the directions of the currents on
each half of an element the horizontal components will be in phase and the
vertical ones out of phase (and will mostly cancel each other).  That leaves
you with primarily horizontally polarized radiation.
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WA2TPU
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Posts: 218




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« Reply #3 on: December 31, 2012, 05:45:20 PM »

WB6BYU Thanks for your knowledge.....

If you put the finger past your thumb and then your middle finger in the shape of a "V" with your hand pointing down to the floor....that's how all the elements would be with maybe 25 degrees between the two wires per element. I thought possibly that it would still be a vertically polarized antenna even at the acute angles of each element. Makes sense what you stated Dale. I also thought about a 40 meter vertical mono-pole log periodic but the swath isn't wide enough for the radials needed per vertical element. I'm trying to build a antenna specifically for 40 meters to work my long time friend Mike-ZS1RJQ. I was hopeful this "swath" I now have due to the loss of some trees from a severe thunderstorm would work out because its directly the correct path to ZS Land.

again, THANKS DALE.
I hope you're feeling better now...A HEALTHY, Happy, and Safe New Year to you.
Best regards and many 72/73.
Don sr. --WA2TPU --
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WB6BYU
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« Reply #4 on: December 31, 2012, 08:10:36 PM »

Such an inverted vee would be horizontally polarized, which isn't going to
be very good for DX at such a low height.

A better approach might be to use elements shaped like an upper-case "I",
using the top and bottom wires for loading.  These can run along the
support ropes.  I tried modeling such an antenna and got about 5dB gain
over a dipole (in free space, before accounting for ground losses) and
15dB F/B, but I used a total height of 32', which might put the bottom too
close to the ground in your situation.  I ended up using loading coils in each
element to provide a convenient means of adjustment.  There will be some
coupling between the ends of the elements (as with a Moxon), so it may
take some experimenting.  The amount of top loading required will affect
the minimum spacing between elements:  I used 3 elements with 24'
spacing, but obviously the array could be made longer.

Another solution would be to use "C" shaped elements, with the top and
bottom loading wires running perpendicular to the support ropes.  Or you
may be able to use the log-periodic monopole design with some creative
form of radials.
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WA2TPU
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Posts: 218




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« Reply #5 on: December 31, 2012, 08:55:44 PM »

To WB6BYU

Thanks Dale. 7 minutes to the New Year here....I'll re-consider my options on the vertical mono-pole log periodic for 40 meters with artistic designed radials.

Again, thanks so much. BE WELL...STAY HEALTHY. My BEST to you and yours for 2013.
regards,
   Don sr. --WA2TPU --
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N4JTE
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Posts: 1158




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« Reply #6 on: January 01, 2013, 03:50:53 PM »

Don if you are thinking wide band 40 antenna with substantial gain and amazing front to back please see my qrz page.
Bob
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WA2TPU
Member

Posts: 218




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« Reply #7 on: January 01, 2013, 04:13:56 PM »

To N4JTE

Bob,
I'm looking for a specifically aimed antenna to fit my swath described that is towards ZS Land. I was hopeful that the wire log periodic I had built would fit the bill as a vertically polarized gain antenna shooting at South Africa. However, after reading Dale's logical explanation I know he is absolutely correct. My swath isn't wide enough for a couple element Delta Loop 40 meter antenna which would be my next choice.
Thanks for your reply Bob.
Best regards and many 72/73. Happy New Year.
Don sr. --WA2TPU --
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