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Re: LF: Capacitive top hat question

from [Andy Talbot] [Permanent Link][Original]
To: [email protected]
Subject: Re: LF: Capacitive top hat question
From: Andy Talbot <[email protected]>
Date: Wed, 4 Nov 2015 21:11:09 +0000
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16 US units of length ~ 4.9m, so that means it's a bit more than half the height of mine.  The top hat is near-enough infinite to all intents and purposes, so its real height is 4.9m.     
My antenna is only 7m high, with much smaller top hat. That amount of top capacitance will drastically reduce the ground resistance, so all more than likely all quite an efficient vertical radiator.   If there is enough buried metal in the ground it could be very good indeed.
so we're probably talking about a similar performance - perhaps an efficiency of -40dB on 137kHz.  That's what mines comes out as, anyway.

Horizontal radiaitors don't when they are close to a reflector.   And the same good ground system that makes it radiate vertically stops the horizontal bit doing anything.   If the ground were very poor, sand for instance with littel wire underneath, then perhaps the horizontal part may generate some ExH, but then efficiency would no doubt be so poor that teh Hpol contribution would be insignificant.

Not sure why you talk about wire separation, he said they are strapped so its just a two wire, fat vertical.  Which is exactly what I use - two paralleled conductors of a twin feed.

Vertical antennas really are quite straightforward to analyse / measure

Andy  G4JNT



On 4 November 2015 at 20:21, Graham <[email protected]> wrote:
I dont think its  that  simple Andy ,
 
16 ft is  not  much  for  136 ,  and the  loop  runs  up from  the  feed  point , which I think  is  a  corner ,, so  at  what  point  is  it a radiating  element  and  which  point  is it   top  loading 
 
Ae could look like a sloping  Y  at  some  point , the  wire  separation  must be  too  much to  act  as  one  ?
 
G,
 
 

Sent: Wednesday, November 04, 2015 8:00 PM
Subject: Re: LF: Capacitive top hat question

A pretty thoroughly top loaded vertical, Heff = Hactual

'jnt


On 4 November 2015 at 19:50, Graham <[email protected]> wrote:
(about 16 fee thigh, strapped together at the base only)

I wonder  what  exactly  is  radiating Chris ?

what  to  you  estimate the  beam  pattern to  be ,  I have the  idea , south  to  SV is down , compared to  say  North TF ? , the  levels  into Iceland  are significant ..

73-Graham



--------------------------------------------------
From: "Chris Wilson" <[email protected]>
Sent: Wednesday, November 04, 2015 4:29 PM
To: <[email protected]>
Subject: LF: Capacitive top hat question

04 November 2015


On my 136khz set up I have a short piece of ladder line (about 16 feet
high, strapped together at the base only) feeding the corner of my
horizontal quad loop, which is about 460 feet in circumference. If I
am TX'ing with WSPR I can walk around under all of the loop and a
fluorescent tube at waist height will light quite brightly. Should the
loop also radiate as well as the vertical section? Sorry for the
probably naive question, I am not sure whether it's normal or not,
thanks.



--


Best regards,
Chris                            mailto:[email protected]





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