|Subject:||Re: ULF/VLF: Tweek resonances - also on 50 Hz harmonics?|
|From:||Markus Vester <[email protected]>|
|Date:||Sat, 15 Jun 2019 09:14:20 +0000 (UTC)|
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Hi Stefan, all,
as you say, the fact that the enhancement is also visible on 1550Hz makes it unlikely that the 1650 Hz boost is really due to an ionospheric resonance. This is corroberated by a plot showing both lines through several nights:
So we still don't know why the 50 Hz harmonics are stronger at night. but probably not due to a resonant reflection.
Another counter-argument is an observation from 2017 where we used colour-DF mode to plot the phase between the twoo orthogonal loops (attached). Due to Earth's magnetic field, in the northern hemisphere tweek resonances come down with pure left-hand circular polarization (magnetic field rotating east-north-west-south). Due to the 90° phase shift the resonances show up in deep red colour. However the 1650 Hz mains harmonic appeared yellow-green, implying linear polarisation with 180° phase between loops.
Regarding the best frequency for a tweek-mode experiment: It looks like there is some variation of ionospheric height from night to night. In some nights the resonance maximum goes down all the way to 1600 Hz, in others it rarely reaches 1670 Hz. Also there is some upward shift with distance to the source. One might speculate that cloud-to-ground lightnings (like an E-field-antrenna) emit less energy upwards, and would tend to come in from further away, with moderate elevation and less time delay between consecutive hops. Note that the resonance usually has a sharper cutoff on the low-frequency side, so that transmitting a few Hz too low may be worse than too high.
Von: DK7FC <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Di, 11. Jun. 2019 17:56
Betreff: Re: ULF/VLF: Tweek resonances - also on 50 Hz harmonics?
Thanks for the images. Interesting!
I checked the spectrograms (i've produced another one from last night) and found that my hum filter was actually NOT enabled, so i do not see a 50 Hz harmonics at 1550 or 1650 Hz, at least not strong enough to measure it's S/N without sferic blanking. Strange...
Also the decribed effect seems to be present at 1550 Hz too, which is unexpected.
Could it be the actual spectrum of the current in the HV power grid? It could be answered by using a stereo soundcard, one channel showing the ULF H field, the other one coupled to a mains transformer (using a resistive divider, dividing down to say 50 mV rms).
>From the observation from last night, which was dominated by cloud-earth lightnings, not by cloud-cloud lightnings, it looks like to cloud-cloud lightnings produce a much narrower maximum near 1640 Hz whereas cloud-earth lightnings have their maximum at higher frequencies, like 1670 Hz, and this maximum is much less narrow. So for amateur tests using H field antennas on both sides, 1640 Hz is the best choice i think.
Am 11.06.2019 17:30, schrieb Markus Vester:
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