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Author Topic: how to: 80m 4-square with ELEVATED radial(s) - interaction of the radials?  (Read 1924 times)
DL2OBO
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Posts: 5




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« on: July 08, 2011, 03:57:05 PM »

I used the search function and read many interesting articles for an hour or so. I didn't find the right thread to "my question"....  maybe it is there, but I didn't find it, sorry.

One of the important questions when building a vertical is:   ground or elevated radials......    this is discussed in many forums, I don't want to start this here again......but:

Q:    In a 4 square with elevated radials - how many radials of what lenght and in which shape should one install to have the best performance?

some of us building a 4 square do not have the chance using ground radials. So we MUST use elevated radials.

I am one of those who "believes" that "4 elevated radials can come VERY close to a 60-120 ground radial system"  or at least I must hope because I have no other chance.
If I could lay down 30 to 60 ground radials per vertical I would do it......
Because I can't I  have to find out, which is the "best way to go" to install elevated radial(s) in a 4 square (phased array).


ON4UN is using 1 elevated radial per vertical but he also has the 160m radials under his 80m 4 square which definately helps.
Using only one radial results in "some" high angle radiation and he like's to have this. I think it is for better F/B ratio of high angle signals and so for attenuating unwanted European signals.  But maybe it is also because with one radial per vertical, there is no problem with interaction between the radials.

So if using two radials in line, the radiation from it would be cancelled and there is less high angle radiation. As far as the radials from one of the three other verticals are not interacting and messing up the system. I would prefer avoiding the high angle radiation. I think without the gorundscreen of that 160m vertical I am loosing enough efficiency, don't want to loose even more.....

Is it better to use non-resonant radials ?  I know it is better to use common coils for each feedpoint ( not a single coil per each radial)(so you need 4 coils for the 4 square)
I have seen a system where the radials ( 2 per vertical ) where folded inside the four square ( like Moxon-Style).

If you have the following possibilities to set up your  ELEVATED radials, which would you choose? (remember: Groundradials are NOT possible)  Any URL to a homepage of someone using it or a call sign I can google for ?

a.)    One quarterwave radial per Vertical   (aka ON4UN)  (but without any 160m ground radials.....)
b.)    two 14m long radials per vertical with a high-Q coil ( 1 coil per feed point) (radials going from the feedpoint 14meter inwards to the center of the 4 square and 14m outwards)
c.)    four 1/8 wavelenght radials per vertical with a high-Q-coil ( 1 coil per feedpoint)  ( which shape ?  x+     or   ++    or     XX
                                                                                                                                                     +X           ++            XX

d.)   two quarterwave radials per vertical aka Moxon ( folded to fit INSIDE the 20m x 20m square)
e.)   one quarterwave radial per vertical -  folded back to cancel the radiation from it, so NO horizontal(high angle) radiation - ( think also the fewest interaction between radials of other verticals ?)

like this:                               O= feedpoint                                   O-----------------|      
                                                                                  ----------------------------------|
not to scale (  see page 57 at  http://www.oevsv.at/export/oevsv/download/QSPArchiv/2009/QSP200910.pdf )


I have 4 fullsize verticals, the feedpoint are at about 9ft above the ground. The radials will be 9ft or I can even rise them to 12ft. I think to remember that the higher the elevated radials, the better.
I think 15ft is a good height for 80m elevated radials

I will set the resonance frequency of each vertical  to 3520khz minus 5% = 3344khz. When all 4 verticals are set up, the resonance will shift up to 3520.
When using the DX-window 3790-3800 I want to use a relay at each each feedpoint to insert a capacitor to shorten the vertical radiators.
Or when using coils for the nonresonant radials changing the tab point of the coil.

I had a lot of RG59 coax which is 75 Ohm and 0,66 velocity factor, so I used 3*quarterwave lenght of it  (measured not calculated!) for each of the 4 feedlines. The advantage is, I have the DF6QV-Hybrid    (like Comtek-Hybrid)
http://www.ov-n15.de/joomla/images/zoom/VFHZZJ/df6qv_final_eng.pdf

and the Dummy load with the Dump-Power-Meter in the shack, not outside in the 4 square center, where it is raining :-) )


It is not the question if elevated radials will work or not or how much better groundradials could be.
Also with elevated radials it is better to have more than just one (I think)

So the question is: In a 4 square with elevated radials - how many radials of what lenght and in which shape should one install to have the best performance?

please have a look at www.dl2obo.com and click on ANTENNA and/or  MY 4 SQUARE INFO


Thanks for reading this, thanks for any help in advance.

please send me / post here  some links to homepages/forums where this is published or post some calls I can google for.
I havn't found too many dispcriptions on 4 squares with ELEVATED radial(s).

73 Tom   DL2OBO / T88DL          www.dl2obo.com



Hotel Hellers Krug***
Altendorfer Str. 19
37603 Holzminden
Tel. 0049-5531-2001
Fax 0049-5531-61266
mail@hellerskrug.de
www.hellerskrug.de

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N4JTE
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Posts: 1147




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« Reply #1 on: July 08, 2011, 10:02:14 PM »

Tom, first place to look is N6LF for the best info. I also used elevated radials on my phased verticals, the best option is TWO, or Four to retain symetry, you are quite right about ON4UN using one with some direction gain due to his already fantastic, in place, ground system that most of us will never achieve. Never built one for 80 meters but from experience I suggest 2 or 4 for best ground return as high as possible. Check for around 38 ohms on each vertical and you will be in the ballpark if using homebrew phasing system.
Best of luck,
Bob
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DL2OBO
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« Reply #2 on: July 09, 2011, 01:37:34 AM »

My feeling also says:   two or four ist the best way to go.   So which shape to choose ?
We know, when using a good high-Q coil to load shortened radials, losses can be very low.
So are shortened radials a way to avoid the interaction of the radials ?
My feeling is: yes.   Anyone ever tried ?
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K2DC
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Posts: 1340


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« Reply #3 on: July 09, 2011, 07:40:13 AM »

Tom,

  I have no experience with a four square, but I have a friend nearby with an 80M four square at about 4m above ground.  He has 6 resonant radials on each vertical, pretty much evenly distibuted in angle.  You will need at least some resonant radials on each.  And you could also shorten the radial lengths with linear loading, rather than using a coil.

73,

Don, K2DC
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DL2OBO
Member

Posts: 5




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« Reply #4 on: July 09, 2011, 02:28:12 PM »

 if one is using a single vertical with elevated radials, it is said that the more radials, the better it is.  OK on that.

But if you are in an array of 2 or more antennas ( 4 square ) then you might get into trouble.... so you try to get better performance with MORE radials but you easily could LOOSE performance because the radials couple into each other an mess up the directivity.........

yet I have not got any URL or direct mails....

I think, I wil try with 2 radials per vertical in line. both 14m long and loaded with ONE coil. with a relay I can choose between to taps on the coil to move from CW to SSB. 
with the two inline radials I have (hopefully) no high angle stuff in the system and two radials seems to be better than just one....

hopefully after the contest weekend some of the big array owner will find the time to have a look at eham.net and fin my question  :-)
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