Hi Daniele,
OK, i will set up the usr file. But it is nothing special, since we
want to display the sferics, we won't have a blanker and/or clipper and
no filtering and no sample rate drift correction is necessary. Just the
same time steps and color palette and so...
Yes, the shielding may be useful, it is worth a try, as long as you
make no closed loop out of the shielding foil arround the loop ;-)
And yes, if no saturation occurs in the soundcard you can do all the
filtering within SpecLab. It works perfectly! Here it makes more sense
to send you a usr file if you want. If you have recorded your reception
of saturday as a audio file, you can re-process the waterfal display
with different settings and may achieve some improvements. You can
totally exclude the band below 5 kHz and above 12 kHz if you want. This
makes the noiseblanker much more effective, as shown last week by the
reception of Michael Oexner on 8970 Hz.
73, Stefan/DK7FC
Am 05.10.2010 07:56, schrieb Daniele Tincani:
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
From:
Stefan Schäfer <[email protected]>
To:
[email protected]
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
From:
Stefan Schäfer <[email protected]>
To: [email protected]
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
|
|
