RE: [PSUBS-MAILIST] retractable buoy

["Jens Laland" <laland@artematrix.org>]

Jay

In order for a cable's characteristic impedance to make any difference in
the way the signal passes through it, the length of the cable must be
closer to a wavelength long for the particular frequency it is carrying.

Most wires will have a speed of travel for AC current of 60 to 70 percent
of the speed of light, or about 640 million feet per second. A narrow
audio frequency band between 300 Hz and 3000 Hz would therefore represent
wavelengths ranging from 213,000 ft and up to 2,132,000 feet - so a cable
would have to be extremely long (and expensive) before it even began to
have an effect on the frequency of a good old-fashion, analog telephone
conversation.

That's why the characteristic impedance of audio interconnect cables is
not something for us to worry about.

Normal video signal rarely exceed 10 MHz. That's just a few inches more
than 65 feet for a wavelength. Those frequencies are getting close to
being high enough for the characteristic impedance to be a factor. High
resolution computer video signals and fast digital signals easily exceed
100 MHz so the proper impedance matching is needed even in shorter cable
runs.

Best regards,
Jens Laland

PS. Did you ever receive my off-list email?

** Coax cable necessary to transmit and receive a radio signal through is
** subject to compression due to depth.  The insulation between the signal
** wire
** and the outer shield is usually a foam, as it collapses signal strength
** will
** fall off.  If shorted, keying the mike on a radio can cause the radio to
** be
** destroyed.  When I was looking at working with the tourist sub SubCat, one
** of the problem areas was a surface float for maintaining VHF
** communications
** with the surface.  It looks like both the hull interface and the antenna
** cable were under constant need of repair.  This sub didn't even dive very
** deep.
**
** R/Jay





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