[sdiy] Patchable polyphonic synth with FM or AM transmission idea

Michael Zacherl sdiy-mz01 at blauwurf.info
Sat Dec 29 04:08:26 CET 2018

> On 29 Dec 2018, at 01:06, john slee <indigoid at oldcorollas.org> wrote:
> Multimode fibre has a lower bound on the cable length. I haven't found a solid reference
> for what that actually is, and I expect it differs across transceiver parts, but I've found a
> LOT of stories of people being unable to get short runs to work and the solution being
> longer fibres. One thread mentioned a Cisco recommendation of 2 metres — something
> about needing a certain amount of attenuation to avoid damaging the hardware at the
> receive end — which would be irritatingly long even in something the size of Keith
> Emerson's Moog

that’s entirely correct: the sensitivity of the receiver is designed to deal with a certain amount of light being received. Good multimode fibres have a typical attenuation of 0.5dB/km (@1310nm).
So the receiver’s just getting “blinded” if you shorten the cable. 
And then you either still use patching fibres with attenuators or add separate attenuators (choose between 5dB and 15dB).
The shortest (networking!) patch cable I found in the catalogue here is 1m, BTW.
And that’s going to be expensive anyway.
Then again, it’s moot because either I don’t understand the idea or “multimode” is just a misconception:
It’s still just one optical fibre with delicate joining technology involved, designed to carry digital signals.
And without appropriate back and forth conversion of the originally analogue signal for each and every connection…
(the rest has been said numerous times here, already)

> Also glass fibre patch leads are pretty fragile.

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