MF,
I just came back from a field experiment, using the short active dipole
which is resonated to 475 kHz (4.7 mH and 10 mH fixed inductors in
parallel plus a few pF (<10) for fine adjustment), with fiber optic cable.
Tests were done in JN49HK94RW, a distance of 2.3 km, see
http://no.nonsense.ee/qthmap/?qth=JN49HK94RW&from=JN49IK00WD Since it
was 17 AM local time i assume there was no skywave component. The
location is an open field without trees or houses in a radius of at
least 30m and without electricity in a radius of at least 100m.
Some results were interesting for me. However i have to do the test
again because my own signal was so strong that some measurements
overloaded the soundcard. I have to reduce the power by 30 dB or so in
the next test, or i have to choose another location.
The signal levels were shown in my battery powered netbook using SpecLab
Software. Noise measurements were done in 1 Hz NBW.
I do not have a high and stable plastic pole so it was just possible to
do the test in 1.75 m above the ground. Tests were done in a horizontal
and vertical position of the dipole. For the horizontal test i tried
both, poiting of the dipole to the TX location and 90 deg rotated to it.
There was no difference. The tests were done with a floating and a
grounded dipole (grounded to a local earth rod, just 10cm into the soil).
Images:
https://dl.dropboxusercontent.com/u/19882028/MF/20130714_165114.jpg
(Receiver)
https://dl.dropboxusercontent.com/u/19882028/MF/20130714_170616.jpg
(Vertical)
https://dl.dropboxusercontent.com/u/19882028/MF/20130714_165421.jpg
(Horizontal)
Results are attached in the image.
Now we can discuss about the results, or not :-)
As i said, i have to repeat the test because a few of the measurements
were to close to the soundcards ADC limit and caused nonlinearity...
73, Stefan/DK7FC
MFtest2.png
Description: PNG image
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