Re: VLF: DF6NM on 8970.002 - again tonight

[wolf_dl4yhf <dl4yhf@freenet.de>]

Hi Markus,

Maybe one of those annoying occasions where the soundcard (or its driver) decides to use a "slightly different" sampling rate for the ADC and the DAC, even if both are the same physical device (chip) ?

Here, for example, the sampling rate of an internal soundcard in a laptop makes a step change (!) when windows plays a sound through it, possibly with a different SR which is not an integer multiple (or fraction) of the sampling rate configured in spectrum lab.

If everything else fails, we'd have to route the output from the soundcard (line-out) back to one of the inputs, and form a control loop in software to eliminate phase glitches. With a GPS reference, we could (ab)use the soundcard to produce truly phase coherent signals, catching up to the original phase even after samples got lost for whatever reason.

73,
  Wolf .



Am 29.03.2012 12:48, schrieb Markus Vester:

My transmission on 8970.002 went off air at 6:35 this morning, and the antenna was taken down for the next couple of days because of windy wx.

 

Unfortunately, the LF harmonic showed that again my frequency was not correct during the first 90 minutes until about 22:30, with a similar behaviour as yesterday, and also during an earlier MFSK transmission (see attached). Immediately after starting SpecLab, the samplerate detector correctly measured the samplerate versus the DHO reference. The lock indicator turned green after the first three blocks, and plausible samplerates were displayed at all times. However the corrections were apparently not applied, and the carrier from the signal generator still drifted with the soundcard crystal. After more than an hour, the carrier suddenly jumped up by about 2 ppm, and within the next 20 minutes settled to the final correctly locked frequency. At first I thought it might be due to some glitch in my LF harmonic measurement or even at DHO38. But it seems to be reproducible so there may actually be a subtle error in the samplerate tracking function. I was using SL 2.77 b08, and will try to look more deeply into this - a simple workaround may be to start and lock SL a couple of hours before operation.

 

Thanks again for watching - it's fun to see the Dreamer's band so populated!

 

73, Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: Markus Vester <markusvester@aol.com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Do, 29 Mrz 2012 12:13 am
Betreff: Re: VLF: DF6NM on 8970.002 - again tonight

Thanks very much for the interest, and to Chris 'WCD for the excellent capture. As the WX is still dry and calm here, I have put the TX back on at 21 UT for another night, with the same parameters as before.

 

My ERP is a bit uncertain, as I haven't measured the effect of environmental shielding on antenna height at VLF. My best guess is somewhere around 7 to 9 meters, which would give around 90 microohms radiation resistance, or 10 µW EMRP at 0.34 A. 

 

The notion of corona being responsible for the noise was suggested by the threshold-like onset of both visual and acoustical emissions. I currently have only very rudimentary "corona rings", by bending the insulated wire into a couple of little loops at each end. I like Wolf's idea of hanging up garden decoration balls, but I'm not sure whether the landlady would find that an acceptable view ;-) Maybe I should look for clear semi-transparent ones, or even partly evacuate them to let them glow real pretty ;-)

 

BTW working back from the corona brightness one gets an optical power of about 1 µW in the visual range. Assuming that at this level the partial discharges are consuming on the order of 10% of the TX power, we find that the efficiency of light generation is only some 0.1 ppm - similar to te efficiency of the whole antenna for VLF radiation ;-)

 

Regarding the noise from the coil, I had originally thought that it might be caused by Lorentz forces in Earth's static field. This gave the idea to cancel the field and thus the noise by permanent magnets mounted appropriately in the coil's vicinity. But this never worked, the magnetic effect turned out to be much too weak to explain the level of 9 kHz noise. Now I think that it is more likely an electrostatic effect from the large AC voltage, combined with static charge buildup on the plastic surfaces. And there is a strong smell of ozone inside of the dustbin after transmitting a while, so there is certainly some degree of partial discharges around the coil buckets.

 

Best 73,

Markus (DF6NM)

 

-----Ursprüngliche Mitteilung-----
Von: Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mi, 28 Mrz 2012 10:27 am
Betreff: Re: VLF: DF6NM on 8970.002

Hi Markus,

Nice work! I can see you in 424 uHz, and traces in 4.5 mHz. You leave a strong trace in 47 uHz, at exactly 8970.0020 Hz! Very nice.
I can see QSB on your signal in that 174 km distance.
What is the ERP?

Go on! :-)

73, Stefan/DK7FC

http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html

PS: Lubos, really an excellent Grabber!!




Am 28.03.2012 09:08, schrieb Chris Dillon:

Hi Markus
Good signals here too in 424uHz and 125uHz (peaking 10dB over the noise) alongside Henny and Uwe.
Nice to see VLF busy!

73 Chris G3WCD


On 28/03/2012 07:50, Markus Vester wrote:

The carrier was on air continuously from 20:26 to 6:36 this morning.

 

Thanks very much to Lubos, as well as to all other live grabber operators. As far as I can see, traces appeared at DK7FC, G3ZJO, OK2BVG, and Paul Nicholson.

 

Best 73,

Markus

 

-----Ursprüngliche Mitteilung-----
Von: Lubos OK2BVG <bvgbob@hotmail.com>
An: _RSGB_LF <rsgb_lf_group@blacksheep.org>
Verschickt: Mi, 28 Mrz 2012 4:24 am
Betreff: RE: VLF: DF6NM on 8970.002

Hello Markus, VLF!

Your signal is nice visible on my grabber in QRSS6000 and traces in QRSS600. In the 6000 window is evident, that we did our VLF QSO in time, when the noise conditions were not the best. 

I have written an article about our qso in Czech. It will be publised in a ham magazine "Radioamater", common known in The Czech and Slovak republic. Some hams would be encouraged to find VLF band by the report. :-)

73!

Lubos, OK2BVG

---

To: rsgb_lf_group@blacksheep.org
From: markusvester@aol.com
Date: Tue, 27 Mar 2012 17:22:42 -0400
Subject: VLF: DF6NM on 8970.002

It's a beautiful night! At 20:25, I have started up a straight carrier on 8970.002 Hz (DHO locked). If all stays well I will leave it on until after sunrise.

 

An interesting observation on the side: In the first few minutes, I drove the amp up to 400 mA antenna current. A little corona became visible near the ends of two of the three topload wires - it wasn't very bright, not unlike 3rd magnitude stars when viewed from the ground 10 m below. But the 9 kHz sound from the antenna itself could be heard quite loudly, which is a potential cause for neighbourhood trouble.

 

Then I reduced the drive to 350 mA where the corona disappeared completely. So did the noise, the antenna became absolutely quiet! All that was left was a little noise from the coil in the dustbin on the balcony, and the transformer indoors. Thus the predominant cause for a squeaking antenna must be corona. The fact that it can be heard at 9 rather than 18 kHz demonstrates that the discharge must have an asymmetric dependence on the voltage polarity.

 

At the same time, wideband electrical noise on the nearby LF grabber antenna went down by 20 dB.

 

BTW If you like you can actually read my VLF frequency from an alias line on the LF TA grabber: It is created by the 24th VLF harmonic, intermodulating with DCF 77, thus appearing on 24 x 8970.002 - 77500 = 137780.048 Hz.

 

Best regards,

Markus (DF6NM)