[Lowfer] 600MRG> Why put a coil under the top hat ???

[P.E.Hamel]

Andy and all,
First Merry and Blessed Christmas wishes to you all.

My justification for putting the loading coil right under the top hat is the 
belief that H-Field radiation should be stretched out as high as possible to 
maximise the radiated power.
The top hat voltage (E-Field) will be the same in any case.

But my top hat is five feet wide and about 120 feet long. (Across the back 
of my lot).
With family and Christmas, I don't have time to dig out the book for exact 
measurements, but what I did was to take my 60 cycle capacitor checker and 
measure the indicated capacity between the eleven wire top hat and unloaded 
downlead to ground (My original 160 meter antenna).
I took that capacity and figured the reactance necessary to resonate at 507 
KC.
I then played with a spreadsheet to give me the best "Q" coil shape.
I even tried to make a spiral coil five feet across (big mistake).

I decided not to make the coil support the weight of the uplead, just run 
weed-eater-line from the ends of the spreader to a point below the coil.
The weight of the 18 wire-uplead on the weed-eater line is enough to keep 
the top flat.
With brass bolts and left-over "white-board" I wound the flowerpot coil.
Two plastic flowerpots and number 10 house wire was heavy, so I found a 
cardboard barrel and laid one layer of fiberglass cloth up on it.
When the epoxy was cured, water loosened the cardboard.
I used the copper tape because another local experimenter had used it 
successfully.
I added two extra turns (just in case) and gave it a coat of green paint.
With good pulleys up and down, I removed turns and found resonance.
With our expansion, I had to add a roller coil in the tuning box to get to 
495KC.

The 600 meter coil makes a good RF choke to 160 and 80 meters.
The resonant point is just above the 80 meter band.
I have relays in the tuning box to switch over to 80 meters for the state 
traffic nets.

On my lot, with almost all radials going southeast, I think this is the best 
I can do.

Does anyone know any DX'er in West Africa ?
If the idea that the direction the radials point helps the signal is right, 
I should have a good signal there.
Again, Merry Christmas and good signals.
Pat W5THT & WD2XSH/6

---- Original Message ----- 
From: "Andy - KU4XR" <ku4xr at Yahoo.com>
To: <lowfer at mailman.qth.net>; "600 meter group" 
<SHMRG at piobaire.mines.uidaho.edu>
Sent: Thursday, December 24, 2009 2:11 PM
Subject: 600MRG> Why put a coil under the top hat ???


> Greetings all:
>
> A few things I have learned over time; What works for one; may
> not work for another, Theory is just that, it works on paper,
> but not always in the real world as it did on the paper.
> ***   AND !!  ***    Don't argue with sucess !!
>
> Thus my question.
>
> For Base applications only, what is the benefit of putting a
> coil directly underneath a top hat ??
> What value should the coil be in reference to the Inductance
> needed for resonance ( a known value ), and still have a
> tunable coil at the bottom  for changes in the antenna due
> to weather and such ??
> Weight considerations and wind load; how should the coil be
> constructed ?? ie; what form material, wire size, etc.
> Is there an optimum placement in the vertical radiator line ??
> such as 1/3rd up, 1/2 , 3/4ths , or right at the top hat ??
> ****   Where can I read up on this ? good information,
> multiple websites will have multiple answers and opinions.
> I would like some good solid information on the topic.
>
> Thank for replies, and Merry Christmas to everyone ::
>
>
>
> Andy - KU4XR - EM75xr - Friendsville, TN.
> LOWfer Beacon " XR " @ 185.29866 KHz ( QRSS-60 )
> Coordinates:  N:  35* 43' 54" - W:  84* 3' 16"
> http://www.myspace.com/beaconxr
> http://webpages.charter.net/ku4xr/
>
>
>
>
>
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