|
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
|
