To: | [email protected] |
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Subject: | Re: VLF: DF6NM on 8970.002 - again tonight |
From: | Markus Vester <[email protected]> |
Date: | Thu, 29 Mar 2012 06:48:03 -0400 (EDT) |
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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 <[email protected]> An: rsgb_lf_group <[email protected]> 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 <[email protected]> An: rsgb_lf_group <[email protected]> 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
df6nm_vlftx_mfsk_unlocked_120316_1030.jpg |
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