[time-nuts] Fury Interface Board: 5MHz needed?

Magnus Danielson magnus at rubidium.dyndns.org
Wed Nov 7 19:01:40 EST 2007

From: Bernd T-Online <BNeubig at t-online.de>
Subject: Re: [time-nuts] Fury Interface Board: 5MHz needed?
Date: Thu, 08 Nov 2007 00:04:19 +0100
Message-ID: <47324473.8050403 at t-online.de>

Hi Bernd,

> In fact the impact on stability is mostly neglectable under stationary 
> operation conditions with rather constant environmental temperature.
> For applications where temperature changes are an issue _and_ highest 
> stability is required, there is no other way than having two separate 
> grounds.
> > Are they running temperature tests with the EFC pin open so they don't see 
> > any problem as the heater current changes?  (or something like that)
> Indeed, many (if not most) OCXO manufacturers run OCXO temp tests (and 
> aging tests with the EFC pin grounded. The undesired ground loop effect 
> can be reduced if the connection is made very close to the pin, and if 
> the inside connection to the PCB ground has low impedance.

If ground loops is indeed a concern, you can reduce the effect relating to the
PCB layout by putting a voltage sense point at the GND pin and run it over to
the EFC buffer op-amp and add that voltage. That way the buffer op-amp drive
the EFC to ground-pin voltage rather than the EFC to signal ground (whatever
that is at whatever point you have).

It isn't the same but if you think of it, the only real solution would be to
have a diffrential EFC input. But then again, you can't win them all, and the
relevance may be very low except for a few odd cases.


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