Re: External Analog to Digital Converters

Meindert Sprang wrote:
"Richard Crowley" <rcrowley@xxxxxxxxx> wrote in message
news:558cmrF24cgrvU1@xxxxxxxxxxxxxxxxxxxxx

Do you mean 25 feet of the cheap plastic extruded stuff,
or 25 feet of proper optical fiber? I don't think the cheap
plastic extruded stuff is defined for use longer than 1m
or so, is it?


Over 15 years ago, when plastic fiber was pretty new, I did some experiments
with transferring an HF signal. The original transmitters could do up to a
couple of MHz over up to 30 feet. I tuned one transmitter with some extra
components and I also polished the ends of the fiber exactly perpendicular
to the the fiber. Instead of using the supplid polishing paper I used a sort
of lime stone block normally used to hone chisels (think grit 16000). All
this resulted in a limit of 12MHz over 250 feet of fibre.

What I learned from this is that simply cutting the fibre with a sharp
Stanley knife with a new blade is not enough to get maximum performance.
Polishing the ends shiny and exactly perpendicular to the fibre is doing
great things for the maximum bandwith. This effectively gives the digital
audio signal steeper flanks and less clock jitter. Oh and sharp radii
smaller than 1" just ruin the cable. It produces microscopic fractures at
the surface of the fibre, ruining the reflection.

Meindert

Sounds like what we were tought back in 85, when I worked at a danish fibre optics communications business. I don't have the course material any longer, and it's a long ago, so..
Of cause, we had specialized tools for cutting and polishing fibres; pretty much needed for achieving gigabit speeds.

--
Kind regards,
Mogens V.

.

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