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Re: LF: Some improvements in VLF Rx

To: [email protected]
Subject: Re: LF: Some improvements in VLF Rx
From: DK7FC <[email protected]>
Date: Thu, 11 May 2017 15:33:50 +0200
In-reply-to: <[email protected]cal>
References: <[email protected]cal>
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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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