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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