Hi Roger.
The soil here is well drained peaty topsoil about 400mm - 500mm deep
on a mixture of slate and shale and although I am 500m from the sea,
I am 75m above the water.
I have no idea what the electrical conductivity is but I imagine
it's probably lower in the winter when my windows get a covering of
salt during storms. It would be interesting to pick on one reliable
ground wave transmission and monitor it through various weather
conditions. It would also be interesting to see how it works lower
in frequency (sub 50 KHz), which is something that I will definitely
look into.
73,
Tony, EI8JK
On 11/08/2010 11:32, Roger Lapthorn wrote:
Thanks for this Tony.
Do you know what sort of soil/rock you have beneath you there?
Here I am on relatively low conductivity chalk/clunch with clay a
few miles to the north west under fenland peat.
If the earth electrode antenna is behaving as a loop (a debated
theory) then it is most effective is the "loop in the ground" is
as large as possible, which would be the case with low
conductivity soil/rocks underneath: the return path between
electrodes would be forced to take a longer route deeper into the
ground. If the soil between the electrodes has good conductivity
then the return current would flow directly making the effective
loop size small.
In the last few days we've had a lot of rain here and the results
on 500kHz last night with the earth electrode antenna suggest the
rain made little difference to performance with reception several
times by PA0A. This is counter-intuitive to me, as I would have
expected levels to be weaker if the soil was wet (loop formed
being smaller etc.). Of course it could have been that the contact
resistance of the earth probes was lower and overall the two
effects cancelled?
Whatever the theory says, the earth electrode "antenna" has some
mileage especially when, like me, there is little space for large
"in the air" antennas. Sure, a big vertical or large loop in the
air would be better (I think), but this is about experimenting and
discovering the limits of possibilities.
Good luck and keep everyone posted if you do further tests.
73s
Roger G3XBM
On 11 August 2010 10:34, Tony <[email protected]> wrote:
I have finally found the time to get some
(radio) work done here and got my 2nd tower finished and I
erected an inverted L, 10m vertical and 30m top rising to 15m
at the far end. I still have the "earth antenna" which is just
a length of wire laying on the ground 80m long and terminated
directly to an earth stake and laying roughly in the same
direction as the top wire of the L .
Comparing the two gave some very interesting results.
10 MHz CW L = S7 earth = S1
7 MHz CW L = S9 earth = S3
R. Bristol 1566 KHz L = 0 earth = S2
Donebach 153 KHz L = S6 earth = S8
DCF77 77.5 KHz L = S3 earth = S5
MSF 60 KHz L = S4 earth = S8
All very non-technical I know, neither antenna was matched or
tuned in any way and was all done about 13:00z.
There was no noticeable difference in the noise level but when
I tried it before the earth antenna was very much quieter
after dark. I will try and repeat this tonight and see what
the difference is then.
Tony, EI8JK.
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