PSN-L Email List Message

Subject: Re: detector design
From: Ron Thompson rlthompson@.................
Date: Sat, 08 Sep 2001 14:17:08 -0230

    I better clarify this, and BTW my job depends on people breaking
things, someone must keep up the good work :-)

    The device is not looking for a phase angle, but simply once the
receiving antenna is moved out of dead centre between the two radiating
plates (where the two fields from the two radiators should produce a
null point) it will capacitively couple to the closest plate and have a
voltage on it that is in phase with the closest plate.  The amplitude of
the signal on the receiver is inversely proportional to the distance to
the nearest plate, and the phase of this signal is either 0 degrees or
180 degrees with respect to the reference.  Vibration magnitude then is
determined by the induced voltage on the received antenna, and the phase
relationship tells us if the receiver plate moved to one side or the
other, but not how far.  I believe that this should work at a frequency
where the length of the coax to the receiving plate should not introduce
a significant phase shift itself, and within the range of cheaper
digital IC's.

Tom Leiper wrote:

> The problem with that approach is the wavelength of the
> RF signal you are nulling is probably thousands (or millions)
> of times the excursion of your detector, so you would have to
> get well up into the SHF range to have short enough wavelengths
> to permit some kind of rational experimentation with tuned
> elements and phase detection. The other detectors to which
> you refer take advantage of the inverse square law and are largely
> frequency independent. You could do it with light just the same,
> except the RF doesn't need to be kept in the dark.

    I was also concerned about the current draw of the lamp in the Opto
2000 design (with respect to solar panel / battery powering the
detector), and that the bulb is the component with the lowest mean time
before failure.  RF oscillators can be built to draw under 5 ma.


> But hey, keep twisting away at'll get it broke yet :-)

 Given half a chance I could get it to work - the wrong way :-)


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Larry Cochrane <cochrane@..............>