[TowerTalk] 4 square for 80

Sat Sep 24 02:13:00 EDT 2016

My mistake - yes it's N6LF.  From QEX March/Apr 2012.  A 2-part issue 
dealing with elevated radials specifically.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

-----Original Message----- 
From: Joe Giacobello, K2XX via TowerTalk
Sent: Friday, September 23, 2016 3:09 PM
To: Jeff AC0C
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] 4 square for 80

Jeff, that appears to be an article by N6LF and not N6BT.  I wasn't able
to download the article, but on N6LF's website
(http://rudys.typepad.com/files/qex-ground-systems-part-3.pdf) he shows
the results of an experiment with elevated radials on 7.2 MHz.  He
compared four elevated radials to 64 ground mounted radials and found
the elevated system had equivalent gain if the radials were elevated a
minimum of four feet above the ground.  I know I had at one time
considered an equivalent 160M vertical and was planning on elevating
them at 18 feet.

73, Joe
K2XX

> Jeff AC0C <mailto:keepwalking188 at ac0c.com>
> Friday, September 23, 2016 3:00 PM
> I see this a lot - need to get the elevated radials up xx feet or 
> whatever. But I don't know how to square that with the N6BT QEX data which 
> shows a improvement in efficiency as the radial is lifted up just slightly 
> from the ground (per QEX Mar/Apr 2012 page 39, figure 16, it's 0.0005 WL 
> approx) - with the slope of improvement flattening out beyond that.
>
> Either the QEX data is wrong, or it's not applicable for some reason in 
> the special case of a 4-square (the article is about a single vertical 
> with elevated radials), or the claims of "moving the radials up made a big 
> difference" are subjective.
>
> 73/jeff/ac0c
> www.ac0c.com
> alpha-charlie-zero-charlie
>
> -----Original Message----- From: Jim Brown
> Sent: Friday, September 23, 2016 1:46 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] 4 square for 80
>
>
>
> Excellent post, Tor. I'm not so sure that I agree with this paragraph
> though. While elevating radials DOES reduce the effective height of the
> radiator, and thus radiation resistance, elevating radials reduces
> ground losses for the same number of radials. In essence, efficiency is
> the voltage divider ratio between Rr and Rg + Rr, where Rr is the
> radiation resistance and Rg is the ground loss. So it can be a tradeoff,
> depending on what's practical at your QTH and how good your soil is.
>
> Based on my 160M experience (4 radials up about 20 ft on a full size
> vertical), I'd guess that 8 ft is pretty good for 80M. Those 4 radials
> at 6 ft had way too much ground loss. On advice from N6BT, raising them
> to 20 ft helped a lot. The feedpoint for those verticals is about 2-3 ft
> high, and the radials rise quickly as they go away from the feedpoint in
> a "gull wing" configuration.
>
> 73, Jim K9YC
>
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> Jim Brown <mailto:jim at audiosystemsgroup.com>
> Friday, September 23, 2016 2:46 PM
>
>
> Excellent post, Tor. I'm not so sure that I agree with this paragraph 
> though. While elevating radials DOES reduce the effective height of the 
> radiator, and thus radiation resistance, elevating radials reduces ground 
> losses for the same number of radials. In essence, efficiency is the 
> voltage divider ratio between Rr and Rg + Rr, where Rr is the radiation 
> resistance and Rg is the ground loss. So it can be a tradeoff, depending 
> on what's practical at your QTH and how good your soil is.
>
> Based on my 160M experience (4 radials up about 20 ft on a full size 
> vertical), I'd guess that 8 ft is pretty good for 80M. Those 4 radials at 
> 6 ft had way too much ground loss. On advice from N6BT, raising them to 20 
> ft helped a lot. The feedpoint for those verticals is about 2-3 ft high, 
> and the radials rise quickly as they go away from the feedpoint in a "gull 
> wing" configuration.
>
> 73, Jim K9YC
>
> _______________________________________________
>
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> RT Clay <mailto:rt_clay at bellsouth.net>
> Friday, September 23, 2016 2:15 PM
> Interesting comments re 4-squares. I currently have up a "wire compromise 
> in the woods" 4 square for 80 that seems to work quite well. Here's what I 
> have done:
>
>
> In the center of the 4-square is a 69 foot R25 tower with non-conducting 
> guys. On the tower are two 15m yagis and a 6m yagi. My 4-square verticals 
> are wires. They go vertical for 48 feet and then head towards the top of 
> the tower- like inverted L's, except the horizontal part of the L slopes 
> upwards. There are ropes tied out to trees to keep them up. Radials are on 
> the ground. I use a Comtek hybrid coupler.
>
> I detuned the tower by dropping a wire from about 20 feet up on a sidearm. 
> This loop is tuned to resonance with a capacitor. I see about a 1 ohm 
> difference in the resistive part of each vertical's Z with the detuning in 
> vs. out.
>
>
> As far as performance, the 4-square is always better than a dipole (nearly 
> flat) at 90 feet for dx stations. For the USA west coast the 4 square is 
> also quite a bit better than the dipole (the dipole favors NE/SW). Even 
> for working W1 from my qth (MS) I often use the 4-square.
>
>
> Various comments:
>
> The reason I chose inverted-L-like elements was that they are easy to make 
> exactly identical, and I get the maximum height possible. With this 
> geometry, the pull-out ropes going to trees don't have to all be at the 
> same height.
>
> In my opinion, if you are height limited, you want to stay away from 
> elevated radials. If you elevate your radials, you are giving up valuable 
> vertical distance which will further lower the feedpoint Z and increase 
> ground losses.
>
>
> I don't think the advice to model the central tower is very helpful. 
> Modeling the typical tower is nearly impossible. Just getting the 
> effective diameter of a triangular tower is nontrivial. Plus add stacked 
> yagis, insulated/noninsulated yagi elements on top, etc. Just plan on 
> detuning anyway.
>
>
> I thought that the hybrid-type controllers (at least the Comtek I have) 
> were really meant to work at 50 ohms. Then for a fullsize vertical, 36 
> ohms + some ground loss is not too far from 50. Obviously they seem to 
> work ok over a reasonable range.
>
> Tor
> N4OGW
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