[time-nuts] Stepping up the output of an OCXO

Don Collie donmer at woosh.co.nz
Sat Feb 3 00:15:57 EST 2007

Why not use an optocoupler as an isolation amplifier? - to the best of my 
knowledge it would provide infinite isolation.
Cheers,.......................................Don Collie

----- Original Message ----- 
From: "Dr Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Saturday, February 03, 2007 12:29 PM
Subject: Re: [time-nuts] Stepping up the output of an OCXO

> Ulrich Bangert wrote:
>> Bruce and Didier,
>> i had the opportunity to measure the output to output as well as the
>> output to input isolation of a diy MAX477 based distribution amplifier
>> very similar to the TADD-1 (but not identical). The output to output
>> isolation was in the order of 75 dB while the output to input isolation
>> was in the order of 90 dB. This is not too bad for this simple design
>> and perhaps more than adequate for most of us time nuts. I have not been
>> able to measure the increase in terms of noise figure but this statement
>> must be read as: The increase in noise figure was less than the noise
>> floor of my equipment. Nevertheless my statement of beliefs is the same
>> as Bruce's one: A single transistor stage may be more easily optimized
>> than a multi-transistor-design.
>> Best regards
>> Ulrich Bangert
> Ulrich
> Since the MAX477 has an input noise of around 5nV/rtHz at 10MHz compared
> to around 1nV/rtHz for a low noise bipolar transistor, the MAX477 may be
> expected to be have a phase noise floor of up to 14dB higher than that
> of an optimised discrete transistor amplifier. This however may not be a
> concern unless one has an OCXO with a phase noise floor approaching the
> state of the art (-180dBc/Hz).
> There are wideband opamps with lower noise than the MAX477 available.
> One could always use 4 MAX 477s inparallel to lower the phase noise
> floor by about 6dB.
> Bruce
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