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RE: LF: Some improvements in VLF Rx

To: <[email protected]>
Subject: RE: LF: Some improvements in VLF Rx
From: "Clemens Paul" <[email protected]>
Date: Sat, 13 May 2017 15:17:21 +0200
In-reply-to: <[email protected]>
References: <[email protected]cal> <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Thread-index: AdLLGi1+N757m3D8Qf6Y62hWW9ciogA0CI1g
 Hi Luis & Stefan,

>>...ill try also a twisted pair instead of the coax
>>...Then you can clearly hear the hum of the QRM noises

>...There will be no improvement. I would stay at coax.

Hum means H-fields.
Coax shield is completely transparent i.e. without any effect to H-fields.

The question is where the hum is being picked up.

73
Clemens
DL4RAJ 



>-----Original Message-----
>From: [email protected] 
>[mailto:[email protected]] On Behalf Of DK7FC
>Sent: Friday, May 12, 2017 2:19 PM
>To: [email protected]
>Subject: Re: LF: Some improvements in VLF Rx
>
>Hi Luis, 
>
>Am 12.05.2017 11:43, schrieb VIGILANT Luis Fernández: 
>
>        
>       I can add an SMD ferrite bead (0805) in the gate
>
>Worth to try.
>
>
>       
>       
>       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
>
>Yes it is 8V/390R = 20 mA. That's a bit much. You could 
>increase that resistor to get about 10 mA, maybe 680 Ohm is a 
>good value.
>
>
>
>       
>       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
>       
>https://dl.dropboxusercontent.com/u/7162072/fotos%20varias/MF/I
>MG_20170430_125017.jpg
>
>Looks like a good place. The 1m probe should be fine. The 
>capacity is given by the probe, about 5 pF/m is the rule. 1m 
>should be fine when the antenna is at this location.
>The only problem seems to be the contaminated ground. You just 
>need to experiment and find the best results.
>Maybe it helps to isolate the probe ground from the mast and 
>feed the cable down to the ground where it has its own earth 
>and an isolation transformer between the TV cable and 
>soundcard... You know...
>
>
>
>       Yes. Using the battery there was no difference, once 
>the ground loop was removed.
>
>Sounds good!
>
>
>
>       That will be fine ! File is here
>       
>https://dl.dropboxusercontent.com/u/7162072/fotos%20varias/MF/V
LF_Soundcard_32KHz.USR
>
>Modified file in attachment. 
>
>
>       Will try also a twisted pair instead of the coax
>
>There will be no improvement. I would stay at coax.>
>Good luck for getting a cleaner background...
>
>73, Stefan 
>



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