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Author Topic: 80 meters vertical delta loop vs dipole...any help.  (Read 2478 times)
VA2NA
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Posts: 26




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« on: November 22, 2012, 04:12:15 AM »

Hi,

I looking for a better performer than my 40 foot high flat top dipole for 80 meter.  I do some research and try severel design in EZNEC and it's look like the Vertical delta loop feeded 1/4 lamba on the side can perform very well for low angle...

Yesterday, i put the vertical delta loop in my tower..apex at 55 feet and side at 8-10 feet high...first difference between eznec and reality...impedance was not as low as supposed..  ( ground loss??) i finally end with 1/4 75 ohms transformer to match the loop..

On air result was not as good as i sould be..  High angle rejection is exactly what is supposed to be..  A/B test agains the dipole show 10 and more dB of difference for high angle...

Low angle now....no difference..i barely show 1/2 db some time but can't confirm...  switching between the 2 antenna show no real improvement on low angle....

I think is related to ground quality of my soil but can someone give some tricks or experience...

Thank

VA2NA
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K3VAT
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Posts: 709




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« Reply #1 on: November 22, 2012, 04:33:49 AM »

Hi,

I looking for a better performer than my 40 foot high flat top dipole for 80 meter.  I do some research and try severel design in EZNEC and it's look like the Vertical delta loop feeded 1/4 lamba on the side can perform very well for low angle...
Thanks VA2NA

I had this exact antenna and successfully used it for several years (150+ DXCC).  The (important) difference was that my mounting point was at 85' - this kept the bottom section high enuf (~35') above the ground so that I wasn't being effected by excessive ground loss.  Additionally, the antenna was out in the open, over 100' away from any house.  Finally, the earth soil condx were good to very good.

Another important consideration about your testing is that your tests are being conducted when the Solar Flux is around 140 with noise levels listed on the QRZ page riding around the S1 or S2 level - not necessarily the best condx for the testing lowband DX.

...  can someone give some tricks or experience...  

This is my experience.  As for 'tricks' - well, we often expect too much out of our new antennas; sometimes later surprised by their performance like when we work the VK9X on 80M.  One has to do the best they can with what their condx are.  Height above ground and far field ground condx (because it is a vertically polarized signal) are perhaps the most influential parameters on antenna systems that we're talking about.  ON4UN's book LowBand DX'ing covers this antenna and reviewing the material may lead you to a better performing 80M delta loop antenna.

GL, 73, Rich, K3VAT
 

« Last Edit: November 22, 2012, 04:40:17 AM by K3VAT » Logged
VA2NA
Member

Posts: 26




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« Reply #2 on: November 22, 2012, 06:54:00 AM »

Hi Rich,

Thank for your input...

My loop is pointing Europe and there a hill no very far away in that direction...i don't know how it will affect low angle radiation VS high angle in that direction... 

I have already done a lot of reading about the Delta loop on the ON4UN book...

My guest is poor performance come from poor ground and the hill...

Next year, i have a 120 foot tower that will be up, and putting the loop higher will be the test.


Guillaume
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K3VAT
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Posts: 709




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« Reply #3 on: November 22, 2012, 07:19:57 AM »

...
Next year, i have a 120 foot tower that will be up, and putting the loop higher will be the test.
Guillaume

Guillaume, Very good.  So just hang in there until next year - then you'll be able to construct a phased 80M delta loops (2) array which will provide you with the potential for worldwide DX on 80M.

73, Rich, K3VAT
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WX7G
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Posts: 6035




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« Reply #4 on: November 22, 2012, 09:09:13 AM »

Guillaume.

The pictures of your station and antenna farm are most impressive!

An EZNEC simulation of your Delta Loop and a dipole up 40' over "medium" ground show the Delta Loop being better at take-off-angles below 24 degress. At 10 degrees it has 6 dB more gain broadside. However, if the hill is more than 20 degrees above the horizon there should be little difference between the two antennas.

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VA2NA
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Posts: 26




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« Reply #5 on: November 22, 2012, 10:02:58 AM »

Here the location here.....the hill is "maybe" the main problem hihi

http://s271.beta.photobucket.com/user/turbogui/media/Hill.jpg.html
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WB6BYU
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Posts: 13234




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« Reply #6 on: November 22, 2012, 10:15:48 AM »

The fact that the measured feedpoint impedance is about double the modeled value
is a clue that something is significantly different in the installation.  My guess is that
the loop is interacting with the tower.

Modeling the loop gives a feedpoint impedance between about 60 and 65 ohms
over a wide range of ground conditions.  Adding a 70' tower shifts the feedpoint
impedance up to about 107 ohms, very close to what you are seeing.  The actual
effective tower height will depend on what you have mounted on it, but that is
a likely source of interaction.


The performance of a vertically polarized antenna is highly dependent on the
earth characteristics out to 50+ wavelengths from the antenna - far further
than most hams do anything to improve it (other than move to a small island in
the middle of the ocean.)  Because of this, an antenna that works well in one
location may not in a different one.
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VA2NA
Member

Posts: 26




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« Reply #7 on: November 23, 2012, 04:23:40 AM »

Yesterday evening, result still the same.

I will turn the antenna on the clearer path and check with station in this direction...  If it's the hill, the loop will be better in this direction..


VA2NA
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WX7G
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« Reply #8 on: November 23, 2012, 05:38:24 AM »

How far horizontally is the top of the hill from the antennas? If 260 meters the hill is a 20 deg obstruction.
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W4VR
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Posts: 1194


WWW

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« Reply #9 on: November 23, 2012, 08:55:24 AM »

I use a bottom-fed inverted delta loop on 40 meters as a driven element.  I use a straight horizontal parasitic reflector and director spaced 20 feet from the loop.  This thing beams towards EU and works like a charm with 30+ dB f/b.  I modeled this antenna using a dipole for the driven element and the f/b is not as good.
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VA2NA
Member

Posts: 26




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« Reply #10 on: November 23, 2012, 02:21:13 PM »

How far horizontally is the top of the hill from the antennas? If 260 meters the hill is a 20 deg obstruction.

221 meters is at 2000 feet of the base of the antenna...convert it in feet...look like i have a 290 feet hill 2000feet away from my antenna....

I don't included the tower in...
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