Re: [amsat-bb] Fiber Optics at RF

[Galen Watts <gwatts@xxxxxxxx>]

> Date: Tue, 22 Oct 2002 00:05:47 -0700
> From: "Greg D." <ko6th_greg@hotmail.com>
> Subject: RE: [amsat-bb] Fiber Optics at RF


> Fiber optics ... hard to shielded well because
> you need a hole to stick the cable into.  We're talking signals in the
> microwave band here, typically.  Also, check out the fiber cable itself.
> Some have a metal runner that goes along side the glass for protection,
> and others have a high graphite content in the jacket.  Both can be
> problems with Rf fields.

I work at a radio observatory with a fiber computer network.  Imagine 
extending the 'hole to stick the cable into' out about a foot so it's a 
tube and you have what we do to shield our network electronics' fiber 
connections.  It's a waveguide above cutoff, the smaller the diameter 
the higher the cutoff. We typically get 60-90 dB of noise attenuation 
out to 15+ GHz, and if one stuffs some copper wool in the end it'll cut 
off out to 100+ GHz.  We're trying to keep the RF in as opposed to out 
but it works both ways and according to some of the most sensitive radio 
reception equipment on the planet it works quite well.  As for metal 
runners and graphite jackets we have both in many places and it makes no 
difference.

The network switch shielded enclosures look like little pipe organs with 
orange and yellow vines growing out of 'em.

73!
Galen, W8LNA
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