Re: ULF: New experiment on 970 Hz, 2/3

[Markus Vester <markusvester@aol.com>]

Hi Stefan,

the screenshot generally looks good. There are some 50 Hz harmonics as well as modulated 33 Hz harmonics but neither seems to contaminate the desired frequency range around 9.70 hectoHz.

However to my eyes, the nighttime spherics seem to be much stronger at low frequency (< 1.2 kHz) than I had expected, though I have to say I'm not at all sure whether that should be so or not. I would speculate that they could be artifacts from higher frequency spherics energy, which may be AM-demodulated by some quadratic nonlinearity in the receive circuitry (e.g. the FET at the input), producing a low-frequency envelope component.

You could check this in a benchtop measurement by feeding a two-tone signal (e.g. 5 and 5.5 kHz, with PEP level approximating that of the strongest spherics) to the receiver, and measuring second-order intermodulation (IM2) at the 500 Hz difference frequency. If this indeed turns out to be significant, you could possibly improve your recording a posteriori by subtracting an appropriately weighted squared signal component. Perhaps this could even be done on the fly using SpecLab's built-in multiplier and adder functions.

Best regards,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Cc: Renato Romero <contact@vlf.it>; Андрей Климов <rd4hu@MAIL.ru>
Verschickt: Mo, 22. Mai 2017 22:37
Betreff: Re: ULF: New experiment on 970 Hz, 2/3

Hi ULF,

So far the recent 970 Hz experiment went very well:

-The transmissions were done as planned. I slightly modified the transmission plan and sent 2 EbNaut messages. The TX was running almost 4 days without interruptions, despite the heavy rain and local thunderstorms.
-When coming back to the RX site, everything was in its right place. The 4x 7 Ah lead gel accus were discharged to 12.1 V only. The recording process was still running.
-I have now a 30 GB .dat file on the USB stick. This file will be analysed in the coming days. I hope to extract a clear carrier and maybe even decode the EbNaut messages?

A first image showing the 0...3 kHz spectrum without filters and blanker: https://www.dropbox.com/s/26bbkfb8q0hs20h/First%20two%20days%20from%20the%20recording.%20No%20filters%20and%20blankers.png?dl=0 (there is a bug on the timescale)

Does this look normal for the experts? Any comments/ideas?
Unfortunately there was a microphonic effect on the E field antenne. I can hear bumblebees from time to time!! ;-)

73, Stefan




Am 17.05.2017 12:07, schrieb DK7FC:

Hi all,

Yesterday it was a perfect day here, sunny all the time, about 26 °C, the forests have a fresh green :-) ...and i put a ULF E-field RX somewhere into JN49LN :-) It will record about 4 days at 24 kS/s.
It is the next experiment on the 309 km band. Since 16.May.2017 a plain carrier is running on 970.005 Hz. I'm again using the modified mains transformer which generates just 5 kV on the antenna. In SpecLab i'm keeping 15 mA antenna current constant, as well as the phase of the signal. That results in an ERP of about 3 nW.

The active E field probe is a 1m vertical and 3m horizontal wire, lifted about 10m above ground.
The attempt is to reach a 27 km distance! First i searched for a 25 km distant location but when i arrived there, there were loads of electrical fences.
In the new location i took a short recording which can be analysed now. The spectrum contains relatively high levels of mains hum, but all in all it looks fine.
So far the QRN levels are relatively low, which is good.
I made a few adjustments to the receiver, hopefully it performs nicely.

I expect maybe a very faint trace in 424 uHz when QRN is low but it should be a clear trace in 47 uHz.

The transmission plan is to keep the carrier on the air until midnight, i.e. 33 hours for the carrier. Then Thursday 0 UTC an EbNaut message (N=5, CRC=4, 100s, 16K21A , 24:00:00 hh:mm:ss) will start at 970.005 Hz. Friday and Saturday will be for a carrier at 970.0025 Hz.

So far the carrier runs very well. Hopefully it will be a successful experiment again :-)

73, Stefan