While congratulating to Joe, Dex and Paul for the achievement :-) I'm
getting intrigued from the "tinnitus" mentioned from Markus and Dex.
I don't guess is the RF giving this effect but could be simply the
coil vibrating like a trasductor trasmitting an audio frequency which
although is in the "audible" field is not audible with easy but
recordered from the brain.
An 8kHz audio frequency could be easily cured with some open cells foam
and a thin (say a couple of cm thick) panel around the coil should
reduce or delete the effect. Due to the high voltage on the coil my
suggestion is to try to use white foam (the black one has some carbon
black inside..) and place the panel 10 cm away from the coil: it could
also be a sort of weather shield for the coil.
Has anybody already tried?
73 Marco IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 3-dic-2017 14.22
A: <[email protected]>
Ogg: Re: LF: W4DEX at 8270 Hz - and VO1NA
Hi Paul,
superb! This is absolutely amazing work.
We can now clearly see the southwesterly origin of nighttime QRN,
presumably South America. A similar effect is apparent on the wideband
twin cardioids at DL0AO, with generally higher noise background from
the west than the east. I am wondering if we are seeing the
nonreciprocity here, suppressing distant QRN from Asia more than from
the Americas. But it might also be related to absorption over a land
versus sea path.
Regarding the spectrogram implementation, three questions crossed my
mind:
- The directional lobe seems rather sharp (also on the old two-loop
spectrogram), slewing the pointer by say 45 ° lets a signal completely
disappear. Linear cardioid magnitude
|B| = mu0 * | Ez/Z0 + Hx cos(phi) - Hy sin(phi) |
should be much smoother, so I presume you are calculationg brightness
using some nonlinear function of angle?
- What is the latency between the end of a one-hour buffer and the time
the latest spectrogram comes online? Could downconvert-and-decimate be
used to speed up FFT calculations for the narrow spectrogram?
- For the three input channels, are you still using three separate
stereo soundcards with individual timing corrections, or one of the
newer multichannel soundcards (e.g. Octo on RasPi)?
Best 73,
Markus
-----Ursprüngliche Mitteilung-----
Von: Paul Nicholson <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: So, 3. Dez 2017 13:06
Betreff: Re: LF: W4DEX at 8270 Hz - and VO1NA
Have a look at
http://abelian.org/vlf/fbins2.shtml
and swing the compass round to 280 degrees.
I've made no alterations to the display settings other
than to use 3-axis signals instead of 2-axis.
Compare with the 2-axis spectrogram
http://abelian.org/vlf/fbins.shtml
to see the difference the extra channel makes.
Still processing data in background to fill in the spectrogram.
It will slowly back date to 2017-12-01 14:00, in batches, you'll
have to refresh from time to time. It'll take a day or two to
catch up.
--
Paul Nicholson
--
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