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RE: LF: Some improvements in VLF Rx

To: "[email protected]org" <[email protected]>
Subject: RE: LF: Some improvements in VLF Rx
From: VIGILANT Luis Fernández <[email protected]>
Date: Fri, 12 May 2017 09:43:03 +0000
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Thread-topic: LF: Some improvements in VLF Rx
Hi Clemens and Stefan
Thank you for the ideas to improve Rx in VLF
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?
Will recheck this sunday if possible
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.
Using SMD SOT23 BF862,215
I can add an SMD ferrite bead (0805) in the gate
Are you sure the FET is working correctly? You can measure/calculate the drain current by measuring the voltage across the drain resistor.
The voltage in the coax down in the shack after the 390R is 6V. Power supply is 14V. So there must be some current trought the FET
Will measure the current
What is the length (or better: estimated capacity) of the probe now and what is the height above the ground/roof/sourroundings?
This is the picture of the 5m mast, which is metal. The last section is a PVC pipe which holds the MiniWhip. The VLF probe is hold in a plastic box
containing the FET and attached to the metal mast using a metal adaptor. So it is quite close to the metal mast, which can provide high capacity ?
Probe lenght is 1m
Did you try to use a bettery for testing the effect on the QRM?
Yes. Using the battery there was no difference, once the ground loop was removed. I did also used a simple way to notice the noise, which is to
route the soundcard to the speakers. Then you can clearly hear the hum of the QRM noises and the clicks which should be QRN
PS: There are a number of settings you could improve in this wideband spectrogram. If you send me your usr file i would send you one back with some changes, if you like.

That will be fine ! File is here
Also it may be worth to start a second spectrogram now, centered on 8270 Hz. It could run in 424 uHz
Is not in the grabber, but I'm running a 283uHz with the 11904 Alpha. It is slow enought to see the improvement when the ground loop was removed
last sunday. And it also shows the shutdown of the Alphas which happened yesterday ;-)
The 32uHz instance in 8270 has been also running for some time. You can also see the noise improvement here
If I get the time, will test the probe in a different place. Not so high but mounted in a totally isolated (PVC) pole
Will try also a twisted pair instead of the coax
Will keep you updated
73 de Luis
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