elevated radials and stuff like that

[K8DO at aol.com]

I am in the process of converting my 2el 160 array to a 4 square, and adding
an 80m 4 sq... In preparation I re-reviewed the available articles and books
on this...  I found I was unhappy with the critical phasing lines (which are
very difficult to re-tune), power lost to the dummy load, multiple driven
 elements, strange matching sections for strange impedences... My thought
process was "if all-driven arrays are so good, why do we use parasitic arrays
for everything else?  Why are not all rotatable beams W8JK  beams or log
periodics, instead of Yagi-Uda?... So, I turned to my trusty computor and
modelled the all driven 4 square and compared it to a parasitic 4 square
(diamond configuration, of course)... The differences are minimal, with the
all-driven 4 square having the better FB (a really, pretty cardoid at one
frequency ) ... (at least, in my quick-n-dirty modeling... I'm talking
'achievable in the real world', here)

So, I am assembling mine as a diamond, with a single driven element and three
parasitic reflectors... A DPDT relay at each element and individual
feedlines/baluns handle the directional chores and impedence matching...  the
antenna is across the common terminals of the DPDT, the additional inductance
for the reflectors is across the NC contacts and the feedline/balun across
the NO contacts...

elevated radials, of course...

Rational discourse welcomed.... flames go to the curb with the kitty
litter...

Denn   k8do at aol.com

Denny

>From john.devoldere at innet.be (John Devoldere)  Wed Sep 25 10:55:58 1996
From: john.devoldere at innet.be (John Devoldere) (John Devoldere)
Date: Wed, 25 Sep 1996 09:55:58 +0000
Subject: elevated radials and stuff like that
Message-ID: <199609250958.LAA13167 at mail.be.innet.net>

hello bruce,

Forgive me for interfering. Let me give you my comments.

>Hi Jay,
>
>I seek your input as you seem to have a good handle on 4sq's with elevated
>radials. 
>
>I have a full size 160M tower, 25G, on an insulated base. About the base I
>have laid down nearly 30,000 feet of copper wire to form a ground screen of
>sorts. The wires, over 100 alone are #6 and #8 copper about 100' to 150'
>long. Also I have laid out 25 rolls of chicken wire each 2' wide and 150'
>long. As I added the wires, (all spare wire gets put to this purpose) I
>checked the feed point with my MFJ and as expected the feed point of the
>vertical dropped as more wire was added. This in an unsophisticated way told
>me that the ground losses I started with may have been eliminated, or nearly
>so. The feed point is now fed with a toroid un-un to match the 28-30 ohm
>antenna to the 75 ohm 3/4" hard line. It works very well on 160. :')
>
>Moving on....I recently (last summer) added an 80M 4sq array, supported from
>this tower. It is a 75 ohm system (ON4UN).


Donno why you call it a 75 ohm system? It uses 75 ohm feed lines because at
the end of the quarter-wave feed lines you get impedfances that give you
less lost power in the dummy than with 50 ohm feed lines.

 Each element is mounted on fence
>posts which put the feed points about six feet above the aforementioned
>ground screen. 

Six feet is pretty low. In my case the radials (1 per vertical) are 17 ft
high. the lower to the ground they are, the more capacitive coupling you
will have between the radials and the ground, and the more radiation loss
.My 1/2 inch 75 ohm hard line is supprtted between the poles and the
cetrally located tower by a nylon rope. I have had no hard line failure in
about 4 years now.              

The phasing lines are 1/2" aluminum hard line with W2DU
>current baluns at the ends. The thinking here was that I wanted to avoid
>having the 160 vertical see the 80m elements as turned up radials. 

your insulated 160 m vertical, if left floating is a 1/2 wave on 80, so it
will couple very badly with the 4 square. Best is to shorten the 160 meter
vertical to ground when you use the 4-square. Just install a relay across
the feed-point, and close it when on 80.

I would
>have elevated the 4 sq further, but couldn't figure how to make the harline
>survive swinging in the breeze.
> 
>The four 80m elements are spaced in a square 66' per side, straight vertical
>and parallel to each other. Each has four radials the same length as the
>vertical portion. (264/f) 
>
>The power at the dummy load with 1500W at the input of the phasing network
>is only about 20 watts at the design freq of 3.75mHz. 

That is excellent!

At 3.5 mHz, the power
>at the dummy load goes nearly to 400W. I can add a couple feet of RG-11 to
>the phasing lines and lengthen each radiator and radial and get the array
>resonant in the cw band easily. 
>
Use the loading system as described in my book, a piece of open wire 600 ohm
line that you insert in either the vertical wire or in the radial. I have
less than 50 watts in the dummy  on both 3.8 and 3.5!


>Hope this isn't boring you..... Given the current thread, what do you think
>the effect of the rather large 160m ground screen has on the elevated 80m
>radials? 

The effect is two fold:

1/ as your radials are rather low to the ground, you will have return
current flowing through the ground as well, and through the capacity between
radial and ground. Now, the better the ground, the lower the losses. So, the
radials will actuallky help you in reducing the ground losses due to a low
radial height. The general rule is: the worse the quality of the ground, the
higher the radial(s) must be. 

2/ the radials will aslo help you obtaining a better REFLECTION  efficiency,
especiallly if you have long radials. with 1/4 wave radials most of the
ground (Fresnel) reflection takes place within the first 1/2 wave from the
antenna.  

Maybe I would be better off is I just tied into this screen and fed
>the 80m verticals at ground level without the current baluns.


 I still worry
>that the 160 vertical would consider the 80m radiators as up-turned radials
>and spoil its performance. 


I have the 4 square around my full-size 160 m vertical, and could not see
any change in radiation resistance when the 4-square was installed. This
means there was no mutual coupling of any significance.  The 160 m vertical
works just as well as before (now 271 ctries on 160).

Well, I really don't have the time or
>instrumentation to investigate this system in depth. I was hoping you or
>someone else on the reflector that is in the know on these matters could
>offer some advice.
>
>On 80M the array is directive, but not so much as I had hoped before I built
>it. On the long distance stuff, sometimes I see f/b on the order of 20 dB.

I also mostly see 20 dB on DX, sometimes 15sB. Sometimnes very little on
close-in stuff, sometimes a lot. It all depends on wave angle. The 4 sqauer
has never outperformed my Beverages for listening. But the 5.5 dB gain over
a siongle vertical is really worthwhile!

>More often, 10 dB. Checking f/b, f/s on close in high angle signals, the
>differences melt away, 5 dB mostly.  I think the array is performing OK, but
>I sure would like to optimize it. Problem is, I don't quite know what to
>change and more importantly I don't know why. 
>
I don't think you can do much more to the 4-square.

>Once I hooked up a relay at the base of the 160 radiator so I could ground
>and unground it remotely. I could see no difference in performance of the
>80m 4-sq either way so I leave the tower element ungrounded. 


That is funny. Unless you mean by "ungrounded" that the feed line is still
connected to the base of the tower. In that case, depending on the length of
the feed line and matching systems you may have, the impedance between
ground and the base of the 160 meter vertical, on 80 meters, may be
"anything", like "grounded". The combination of what's connected may detuned
the 160 meter vertical enough for it to be transparent to the 80 m 4-square.
But if the 160 meter 1/4 wave vertical is left floating without anything
connected, I bet you it will couple like hell to the 4-square!

375' of 3/4"
>hard line away from the feed point is an Ameritron antenna selector box. The
>un-used antennas are grounded at that point. Both the 4-sq and the 160 vert
>are fed from this remote switch. Each with 375' of 3/4 hard line. 


Here is the answer. 375 ft of hardline and a short is what detunes your 160
m vertical!


>
>Sorry this takes so long to explain..... 
>
>73,
>Bruce
>AA8U
>
>
>

73  john

----------------------------------------------------------------------------
john.devoldere at innet.be
Call us in all major 1996 contests: ON4UN (OT6T in WPX)
John Devoldere (ON4UN-AA4OI)
POBOX 41
B-9000 Ghent (Belgium)


>From headrick at radar.nrl.navy.mil (Jim Headrick)  Wed Sep 25 19:25:56 1996
From: headrick at radar.nrl.navy.mil (Jim Headrick) (Jim Headrick)
Date: Wed, 25 Sep 1996 13:25:56 -0500
Subject: Radials and low angle radiation
Message-ID: <v01530500ae6f25c3fed9@[132.250.182.180]>

> If I could, I would put my radial wire under the ground.  But nonetheless
>I think Dick's
>work has value and it showed me that if I want to reduce the high angle
>radiation I had
>better make my radials 1/8 wave each and tune them to resonance with a
>single common
>inductor.
>

If your radials (ground screen) are going to lower the radiation angle they
have to be very long, order of tens of wavelengths.  The quarter wave or so
radials are to reduce ground losses and stabilize your antenna impedance.

73    Jim


******************************************************************
*      Jim Headrick (W3CPB) --->  headrick at radar.nrl.navy.mil    *
******************************************************************



>From snace at tdrss.wsc.nasa.gov (Steven Nace)  Wed Sep 25 20:45:34 1996
From: snace at tdrss.wsc.nasa.gov (Steven Nace) (Steven Nace)
Date: Wed, 25 Sep 1996 12:45:34 -0700
Subject: 2 radio ops- headphone questions
Message-ID: <v02120d04ae6f38a0e348@[192.77.86.212]>

My present 2 radio set-up stinks. This includes the way I listen to 2
radios at once. I am soliciting methods or preferences from those of you
that have success with 2-at-once.

One question is: If 1 rig is audible in each ear, do you have a serious
handicap when one radio is turned down all the way? Does this present an
'inbalance' in your head? Is there a way to counteract this inbalance?

Any advice and experiences shall be appreciated.

Thanks in advance

KN5H not KN5S

 ____________________________________________________________________
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