Re: VLF: VLF at different locations and QRN as a function of daytime

[Daniele Tincani <danieletincani@yahoo.com>]

Hi Stefan, VLF,

 

I agree with you. With 60 seconds/plot I think > 12 hours are possible on my screen (1280 pixels max horizontal size, 1024 used normally). Say 5.00 UTC to 17.00 UTC for example. Please send me the .usr file to load.

 

Currently my loop is connected to a zero-impedance (ideally) pre-amplifier (a design by Renato Romero IK1QFK and Marco Bruno IK1ODO, build around the LT1028A op-amp).

The cutoff frequency should be (in theory) fc = R/(2 x pi x L). If my measures were not wrong some time ago, for my loop I should have R=3,7 ohms, C=186pF, L=2,9mH which give an fc of about 203Hz (theoretically). The resonant frequency should be > 200KHz, so I hope the response curve is fairly constant over the VLF range. A low-pass filter with about 50KHz cut-off is included in the pre-amplifier circuit.

 

I'm planning to add some shielding to the loop by means of metal tape to see if I can get an improved balancing and better rejection of common-mode noise (quite a quick and unexpensive attempt). I also thought about adding a switchable passive high-pass filter with say 5KHz cut-off before the amplifier, but an analysis of my signal made by Renato months ago showed that there wasn't any input saturation at low frequencies, so a filter will probably help poorly in reducing local noise in the dreamer's band. Anyway, I will try and see what happens :-)

 

Regards

Daniele

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From: Stefan Schäfer <schaefer@iup.uni-heidelberg.de>
To: rsgb_lf_group@blacksheep.org
Sent: Tue, October 5, 2010 1:19:56 AM
Subject: Re: VLF: VLF at different locations and QRN as a function of daytime

Hello Daniele, VLF,

Yes, sharing the same usr file could be useful. My grabber is currently covering about 13 hours in the wideband window but 24 hours makes sense i think. The sampling rate should be 48 kS/s since most amateurs have no 'special' and expensive soundcards.

If you want i will arrange a suitable usr file? But the time that is covered is a function of the size of your monitor so we should define the capture size in pixels. I am using 980 pixels on my grabber...

The next question is the frequency response of differnet RX antennas (due to the design). If the lower cut off frequency is above 6 kHz, it might be difficult t compare. Maybe it is best you and others who want to take part of this idea, just show a capture from 0...24 kHz and some hours (> 10) to get a first impression?

73, Stefan

Am 04.10.2010 23:56, schrieb Daniele Tincani:

Hello Stefan, VLF,

 

would a wide-band capture over 24 hours from my QTH/receiver be of some interest for you? If so, I think I could be able to send the results to you by the end of this week or so (hoping batteries last enough :-)). Probably it could make sense to share the same .usr file for SpecLab so that to ensure a bit of consistency when comparing figures from different locations.

My sound card support 96KHz sampling at 24 bits/sample, but I found that card's noise looks much better when sampling at 48KHz.

 

Best regards

Daniele

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From: Stefan Schäfer <schaefer@iup.uni-heidelberg.de>
To: rsgb_lf_group@blacksheep.org
Sent: Mon, October 4, 2010 11:20:33 PM
Subject: Re: VLF: VLF at different locations and QRN as a function of daytime

Hi Daniele,

No problem about the callsign ;-) On VLF you don't even need one for transmitting, hi.

Oh, you are in JN53EM, i haven't known that. The distance is 707 km! This is the 3rd best distance at all! Unbelivable, for a antenna in that location, very fine!!!

I hope cou can improve your RX situation if this is your goal.

And i hope i can transmit more meaningful messages the next time ;-)

73, Stefan/DK7FC

Am 04.10.2010 14:57, schrieb Daniele Tincani:

Hello Stefan, VLF,

 

frankly speaking, it is still unbelievable to me that I was able to catch a faint trace of your signal and see it appearing on my PC. This is because of the intense hum at my location and the unsophisticated reception system that I use. Anyway, I'm glad to read your opinion that the screenshot I captured was really showing your tx :-)
I'm also interested in supporting your idea of collecting information about local QRN at different locations. I'm aways looking for simple-to-build solutions for improving my setup. May be some helpful information could emerge from this data analysis you are proposing.

For the time being, these are the information you have requested: the locator is JN53EM. As for the callsign, I'm sorry, I haven't one. I'm only "registered" as a SWL and my identifier is I0169LI (http://www.qrz.com/db/I0169LI/).

 

Cheers

Daniele