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Donít Trust the Indicators

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zeeglen
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Re: Cabletron
zeeglen   8/4/2014 1:05:33 AM
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@David 3 dB of optical loss is equivalent to 6 dB of electrical loss.

With optical the power is directly proportional to the current in the led or laser (the voltage remains almost constant), and the same happens in the photodetector at the receiver in that the current is directly related to the incoming optical power.  Therefore half the optical power (-3dB) results in half the current which results in half the voltage at the output of the transimedance stage.


But electrically half the voltage and current is -6dB since electrical power is related to the square of the voltage or current.  With optical there is no square in the relationship, the power is linearly related to the current.

I used to get a chuckle years ago when all the FDDI hype was for that newfangled optical fiber and the magazine articles compared fiber to copper and breathlessly announced "...only 3dB per kilometer..." when in reality it was 6dB/Km once converted back into electrical terms.

David Ashton
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Cabletron
David Ashton   8/4/2014 12:09:23 AM
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Hi Glen.   I have used some cabletron gear before - though not the same as above - and in general it was reliable, good gear.  But that link indication is definitely a bit dodgy.

I am puzzled by your last remark: "Note: 3 dB of optical loss is equivalent to 6 dB of electrical loss."  How so?  3 dB is half power, why should optical be different?

MeasurementBlues
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No more Cabletron
MeasurementBlues   8/3/2014 12:50:25 PM
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Cabletron was based in Rochester, NH. They used to run emplyments ads in the Boston Globe. cabletron.com now goes to Extreme Networks.

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