ULF,
It was a clear, cold and sunny day again and finally i was testing the
new large 2.97 kHz coil on the roof:
https://dl.dropboxusercontent.com/u/19882028/ULF/20161204_153126.jpg
Not a good idea on MF or LF, but on ULF is can be a good idea to put a
resistor in series to the coil. I put 500 Ohm in series. This helps to
attenuate eventual HV transients, makes the resonance curve a bit
flatter, so the peak is easier to hold.
500 Ohm and 0.1 A, that just a loss of 5W, quite affordable.
https://dl.dropboxusercontent.com/u/19882028/ULF/20161204_153113.jpg
Unfortunetely i found that the actual resonance region is adjustable
from 2993...3130 Hz. So the inductance is still to low :-( I've been
quite sure that my antenna replacement capacity for resonance tests in
the shack has the right value. So maybe other effects like an
additional capacitive load by the things standing arround in the shack?
Or a different behaviour of the residual antenna + frozen ground
capacity on 2970 Hz?
At least it was possible to get 100 mA anyway, just by applying some
more voltage to the antenna. The PA is now running at 20V and less than
1A, most of that are PA- and transformer losses. Anyway i have 12 kV on
the antenna! That's ULF!
I was planning to bring the coil down to the shack anyway, after the
65km experiment which will start in a few days i think. Then i can add
more turns to come closer to 2970 Hz.
With 70 uOhm radiation resistance the resulting ERP is now entering the
microwatt range: 1.2 uW on the 101km band.
A stable carrier at 100 mA was sent from 12:50 UTC to 14:24 UTC.
I tried to measure the antenna current with a true rms digital
multimeter, shielded by aluminium foil, measuring on high potential.
But the measurement was wrong anyway. The permanent installed analog
amperemeter and SpecLab gave a correct measurement. Tomorrow i will
check the antenna current measurement on high potential with a
calibrated analog amperemeter.
For the 65km experiment i want to transmit some DFCW-12000 again as
well as an EbNaut message. The RX site will be in JN39VH :-)
73, Stefan
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