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Re: LF: Re: Comparing earth-electrode v. Marconi antenna on 472kHz

To: <[email protected]>
Subject: Re: LF: Re: Comparing earth-electrode v. Marconi antenna on 472kHz
From: "Graham" <[email protected]>
Date: Wed, 9 Jan 2013 01:10:57 -0000
Importance: Normal
In-reply-to: <8EFF74C5288B4CC1B0776D52DBE13A77@gnat>
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Could  be  on the  grounds  of  part of a  magnetic  loop  , where  the  circuiting  current  is  bolstered  by the  'diffused '      return  path ,  I was thinking of the  high  level  of  circulating  currant   causing  the  radiation as  opposed to  a 'wave  size'  array    
 
G..

From: Alan Melia
Sent: Wednesday, January 09, 2013 12:10 AM
Subject: LF: Re: Comparing earth-electrode v. Marconi antenna on 472kHz

There is nothing wrong with the "science" of doing simple experiments Roger ......The bad science is if you try to read too much into them......which you have not done. Your results do align with the books in the subject though most are for ELF. It doesnt work this way for everyone it depends on local ground conditions.....thats why there is always so much discussion :-))
 
I cant remember the detail but the skin depth of your ground at 500k is probablty quite shallow but it probably could still be several feet  giving a reasonable area loop, and the conductivity must be quite good.
 
Graham's idea of a TWA is feasible but I think it is too short(normal requirement 300 to 900 m) to have directionality, not  terminated, and too low ar this frequency. TWAs usually work best on receive over poor ground and would very inefficient as transmitting aerials. But any bit of wire will act as an aerial and there is no guarantee there is a single mode of operation :-))
 
 
Alan
G3NYK
----- Original Message -----
Sent: Tuesday, January 08, 2013 9:06 PM
Subject: LF: Comparing earth-electrode v. Marconi antenna on 472kHz

This evening I've been noting my WSPR S/N reports from stations across the country and nearer Europe using my 9m long Marconi antenna (an average arrangement for a small garden plot like mine - but not the best) and comparing these with the reports last night when I was using just the 15m baseline earth-electrode "antenna". I crudely plotted the "improvement factor" in dB on a polar plot. Each dot represents a station reporting my signal with the dB improvement over the earth-electrode antenna plotted on a 0-20dB scale out from the centre. This is not good science, it is G3XBM science I'm afraid, but it give a fair idea of the difference and how direction affects this (see attached rough polar plot).

Although in some directions the difference is very little, in other directions the reports are up to 14dB better on the (omni-directional) Marconi.

My conclusion is that the earth electrode antenna is behaving somewhat like a loop with some directionality along the line of the earth-electrode baseline and a null off the sides. With stations receiving me off the sides there is most improvement with the Marconi, and less difference with stations end-on who were getting a reasonable signal with the earth-electrode antenna.

CONCLUSION: the simple, stealth, earth-electrode antenna is a VERY useful antenna on 472kHz as long as one is prepared to accept a 2-14dB loss compared with a "small garden" Marconi. In all honesty, I am getting better reports on the Marconi but few new stations are copying me: most could copy me on the earth electrode antenna.

I shall run WSPR overnight to see if any more distant stations copy me, then probably put away the 472kHz gear and Marconi for a while to find another interesting challenge - possibly something on 10m or VHF.

These last few days have been fun, and that is really what this hobby is about.

73s
Roger G3XBM
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