At 10:49 AM +0000 5/15/12, time-nuts-requ...@febo.com wrote:
Date: Tue, 15 May 2012 08:59:04 +0200
From: Attila Kinali <att...@kinali.ch>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: Re: [time-nuts] wwvb weak on east coast especially when the
pre-amps under water.
Message-ID: <20120515085904.19669d7edd8b95454f176...@kinali.ch>
Content-Type: text/plain; charset=US-ASCII
On Mon, 14 May 2012 18:01:01 -0400
Joseph M Gwinn <gw...@raytheon.com> wrote:
Modern outdoor enclosures use a filter of some kind, but the underlying
principle is the same.
I don't know what other types are around, but we use vents with
a gore-tex foil over them. Keeps water out but lets the case breath.
This prevents any pressure build up, which would then start to suck
water in from the seal.
Gore-tex blocks liquid water (and dust), but allows water vapor to
pass, so one can still get pumping and the accumulation of condensed
water. Where are your enclosures used, and how exposed are they?
As for the other methods, so far the following have been discussed:
Box with long tube, where the tube volume exceeds the tidal volume of
the enclosure, so outside air never manages to get to the enclosure.
Typically, the tube is plugged with some cotton wool, to keep insects
out.
Box with short tube and filter/dessicant. The Gore-tex film is a
filter, but not a dessicant. A box with medium tube and filter plus
dessicant at the box end can be very effective, the medium tube
reducing the rate at which the dessicant is exhausted.
Box with short tube that opens on conditioned space.
Totally hermetic box. Very effective, but very hard to do in
practice, unless the box is small and strong.
Box where positive pressure is maintained using dry air, so all leaks
are outward and the dew point is never reached inside the box.
Joe Gwinn
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