Hi Luis,
Am 08.05.2017 10:57, schrieb VIGILANT Luis Fernández:
The VLF espectrogram has got
clearer, but still contaminated. Specially at night, probably due to
street led lights in the area
Yes the noise background is dominated by 'horizontal' traces, not by
vertical traces, i.e. QRM (unwanted) instead of QRN (expected in a
clean location). This domination is very expressed. So either your
ground is hopeless contaminated or maybe something is even wrong
connected?
I'm using a separate first Fet
at the probe, connected by aprox 15m TV coax. Would it be better to use
twisted pair or
keep all the preamp up, close to
the probe ?
Are you using the BF862 as the first FET? I observed VHF oscillations
in the past and would now suggest a ferrite bead as close as possible
to the gate of the JFET.
Are you sure the FET is working correctly? You can measure/calculate
the drain current by measuring the voltage across the drain resistor.
The TV coaxe is fine.
What is the length (or better: estimated capacity) of the probe now and
what is the height above the ground/roof/sourroundings?
Did you try to use a bettery for testing the effect on the QRM?
73, Stefan
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