----- Original Message -----
Sent: Wednesday, January 09, 2013 1:10
AM
Subject: Re: LF: Re: Comparing
earth-electrode v. Marconi antenna on 472kHz
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..
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
