Hi Rik.
I take your point, but I did say that it was "non-technical"
The earth was the main station earth which is a short (1.5m) length of
22mm copper pipe to an earth mat and radials and was the same earth used
for both antennas.
The receiver was AC powered but there was no trace of a signal at all
between connecting the different antenna wires
But a question for the techs, when does a long "earth" antenna become a
Beverage antenna ?
Or, how short can a Beverage antenna be before it ceases to be any
practical use ?
73, Tony, EI8JK
On 12/08/2010 01:34, Rick Wakatori wrote:
Hello Tony,
Show us your RX earth terminal side and whether AC voltage supply or
DC battery did you use for the experiment. AC line can be a good long
antenna for receiving.
7L1RLL Rick
On Wed, 2010-08-11 at 16:16 +0200, Rik Strobbe wrote:
Hello Tony,
measuring voltages on untuned antennas is "tricky", in particular with
small electrical antennas (compared to the wavelength) as these tend
to have large reactive components.
On 60kHz the L-antenna you described has a reactive component of about
10000 Ohm while the resistive part will be some 10's to some 100's Ohm
(mostly loss resistance). So properly tuning the antenna will increase
the RX voltage by several S-points.
Ground loop antennas on the other hand seem more broadband.
Maybe that explains why they perform better at lower frequencies
( compared to the untuned L-antenna).
Anyway, your L-antenna should perform well on 500kHz.
73, Rik ON7YD
______________________________________________________________________
Van: [email protected]
[[email protected]] namens Tony [[email protected]]
Verzonden: woensdag 11 augustus 2010 14:05
Aan: [email protected]
Onderwerp: Re: LF: Earth antenna
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.
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM GQRP 1678 ISWL G11088
|
