[time-nuts] Advice on 10 MHz isolation/distribution (Clay)

[life speed]

Message: 6
Date: Thu, 11 Feb 2010 12:38:58 -0500
From: "Bob Camp" <lists at cq.nu>
Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution
    amplifier(Clay)

Hi

I'll grab the one on the hybrid.

In this case hybrid is referring to a construction technique.

The circuit shown was originally fabricated in a TO-8 package with chip and
wire construction. It was certainly made using thin film or thick film
technology on a substrate. Based on the number of components and size of the
part, I'd bet that the resistors were printed on the substrate. 

When you are using that kind of construction approach there are some good
things that happen and some bad things. The circuit topology is modified to
work with the construction technique. In this case the Ft's of the
transistors are quite high. Taming them on a substrate (alumina or glass) is
a very different thing than doing it on a PC board. 

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Is your OCXO vibration isolated?

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Bob

OK, you're talking about chip-and-wire, or hybrid construction.  Really, at 10 MHz, that seems unnecessary.  Of course, PCB construction will introduce some parasitics.  Transistors with lower Ft could be used.  Additionally, there are bandwidth-limiting techniques like adding feedback capacitance.  I suppose this would come at the expense of high-frequency isolation.  But for my application isolation is important in the 10's of MHz, not much higher.  Having built a couple transistor circuits over the years, I am aware of what can happen when a transistor in a low frequency circuit has an Ft of multiple GHz.  Usually oscillations.  I imagine a high Ft enables the isolation to extend to very high frequencies.

Yes the OCXO is vibration isolated or the system wouldn't produce good phase noise in operation.

Clay