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I got a complaint from the neighbourhood about
acoustic radiation from the coil! So I interrupted the carrier for a few
minutes around 12:35 and improvised a foam package for noise
mitigation.
BTW It is quite remarkable that an air coil
vibrates at 9 kHz and not 18 kHz, as Lorentz forces between windings should
be a purely quadratic effect. I presume that the vibration is induced by the
earth field - at only 50 uT it's amazing how strong the effect still is! The
loudest part of the setup is the ferrite transformer, probably due to
magnetostriction, with bias from some remanent core
magnetisation.
Best wishes for a quiet Sunday,
MArkus (DF6NM)
----- Original Message -----
Sent: Sunday, October 10, 2010 12:02
AM
Subject: Re: VLF: Transmit hardware
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...
XYL has warned no coils on the roof here!.............
hee. |
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