Für die "Techniker" und Bastler unter uns. (Also leider nix für mich
)
Scheint übersetzt Spule o.a. zu sein?
The Hum can be detected and recorded using
coil detectors: 700 turns .010" diameter enameled wire wound on a 12" plastic bucket.
A 0.1uF capacitor in parallel tunes it to broad resonance at 200Hz.
Connect this to the MIC input of a battery powered cassette tape recorder
with 9ft of coax to separate the coil from e/m noise from the recorder.
70 turns of wire on a wooden frame 1 meter square, tuned with a
capacitor.
Ferrite rod 7" long, 1/2" diameter. Use .004" enameled wire and wind
a coil 1" diameter, 3/4" long in the center of the ferrite rod. Coil
resistance should be about 500 ohms. 0.1uF capacitor is connected in
parallel for tuning, vary the coils to tune either for 150Hz or 250Hz.
Coil output feeds an audio preamp with 100x gain, which feeds an op-amp
active filter tunable 30Hz to 300Hz. Filter output goes to an active
rectifier stage, which feeds a meter, chart recorder, etc.
Two ELF carrier waves are detected, 150Hz and 250Hz, amplitude
modulated with 0.5 - 1.5Hz.
The 150hz and 250hz signals do not rise and fall together, and the
modulation isn't the same. The field strength is *not* proportional to the perceived loudness of
the Hum. But if the modulation consists of sharp rises and falls
combined with a high signal level, this appears to produce a loud hum.
The perceived loudness may be proportional to rate of change of
modulation. The movement of a signal level meter seems synchronized
to the modulation of the hum.
The loop antenna indicates the
signal direction is on a North-South line.
On a 30mile East-West base line using the loop antenna for direction finding,
taking multiple readings along the line, no change in angle was
measurable, indicating a very distant source.
Taking a detector into a railway tunnel with 15ft - 20ft of soil and
rock overhead did not measurably attenuate the detected signal.[/quote]
Die eigene Website von John Dawes* exisitiert anscheinend nicht mehr
(Auszug ist von einer anderen Webseite):
http://amasci.com/hum/bristol.html(*Er befasste sich intensiv mit "The (Bristol) Hum" / UK)
Es hörten Hunderte, als es "abgestellt" wurde, wollten Regierende nicht die Ursache bekannt geben!
Auszug aus seiner damaligen Webseite:
Zitat:
On their return to Bristol the group contacted the local authority and Bristol Member of Parliament Arthur Palmer and persuaded them to investigate the matter. Arthur Palmer and the investigating team finally claimed to have traced the source and stopped the Hum,
however, the authority refused to reveal the source saying "we have stopped it, be satisfied with that"
