Hi Mal.
It is most definitely directional or at least my permanent earth dipoles
are.
I have two at 90 degrees laid out as a cross with the radio shack at the
centre. Both have wires 80m long laid on the ground in places and draped
over shrubs in places and rises in one place to about 7 ft where it goes
over a gateway. The total length of each dipole is 160m and one wire
goes to the centre of the coax and the other to the screen ... no
station earth used and no resistors at the far ends.
They are laid out north/south and east/west and a station due east of me
is 12 dB down on the N/S and vice versa, from VLF to HF.
They are also very quiet and fairly immune to local QRM especially
compared to the inverted L which is pretty much unusable for weak
signals at night and weekends to to computer and TV hash from the
grandchildren playing games.
73, Tony, EI8JK.
On 15/12/2010 17:00, mal hamilton wrote:
Hi Tony
Nice to see you join in on the discussion.
This is an interesting experiment and my first thought would be that it is
behaving like a Beverage antenna. Direction might indicate something for
instance rotate it 90 degs and check the signal strength
One experiment I thought might be interesting is to resonate a low long wire
height say 20 ft and 200 ft long earthed by a spike at the far end and feed
the near end with a signal. The signal source sent via coax, the centre pin
to the wire and the earth shield to a ground pin.
then
put an atu between the coax shield and the near ground pin and resonate it
if possible ie a tuned ground as well as a tuned/resonated wire.
This antenna would really be a Grounded quad loop, the 200 ft wire plus 20
ft height x 2== 240 ft total and the earth/ground would be the other half ie
total length 2 x 240 == 480 ft. The theory is that the ground would provide
a mirror image of the wire above it. So for vertical quad loops, delta loops
you only need build one half above ground and the ground provides the other
hal
There was an article years ago in QST magazine by Belrose that explained the
theory for an 80m grounded delta loop.
Natural resonance should be 2 Mcs
Resonate the wire at a frequency of choice
This is all interesting but I prefer to use a more convential antenna system
that I know will work
73 es gl de mal/g3kev
----- Original Message -----
From: "Tony"<[email protected]>
To:<[email protected]>
Sent: Wednesday, December 15, 2010 3:07 PM
Subject: Re: LF: Re: Earth Antennnas - General question
Hi Mal& LF
Your comments prompted me to carry out some simple tests today.
I layed out a 25m length of Thompson RG 214/U double screened coax on
the lawn and connected the centre conductor at the far end to a
stainless steel rod abt 300mm long pressed into moist soil.
In the shack I measured the signal strength of DHO-38 at -51 dB with the
coax screen connected to the station earth.
I then disconnected the station earth and still measured -51 db and then
I strapped screen and conductor together and still measured -51dB
Then I added an extra 10m of coax and elevated it all to an average of
2m above the ground and carried out all the above again with absolutely
no difference in signal strength.
Finally I pulled the earth rod out of the ground and the signal dropped
to -94 dB and then I disconnected the coax totally from the earth rod
and the signal dropped to -102 dB.
Make of that what you will.
I also out of interest connected my MFJ antenna analyser and found that
the SWR was fairly flat across the whole spectrum (between 2:1 and 8:1)
from 1.8 MHz to 150 MHz, although I don't think I will hear much on 2m
73, Tony, EI8JK.
.
On 14/12/2010 23:47, mal hamilton wrote:
Gerhard
Yes the antennas described by Stefan and Roger and others are of the
LOSSY
variety and similar to Beverages.
I have made this observation before. I cannot see how these elevated
antennas can be considered Earth Mode since they propagate a signal into
the
ether to be received at a distance by another elevated antenna several
metres above ground.
de mal/g3kev
----- Original Message -----
From: "Gerhard Hickl"<[email protected]>
To:<[email protected]>
Sent: Tuesday, December 14, 2010 9:06 PM
Subject: LF: Earth Antennnas - General question
Hi all !
I was following the whole discussion about the so called "earth-mode"
and the used antennas with interest.
Mal told us that he sees those antennas as "lossy dipoles" while others
stated they are "true" earth-antennas.
I don't have the theoretical background to tell you why but out of my
feeling, all those antennas described remind me on the well-known
Beverage-Antenna system.
Two wires of any layout, diameter, height and length terminated by a
"resistor"...the soil.
Could that be a way we could look at this kind of antenna?
And if so, what would it explain?
73
OE3GHB
Gerhard
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