[time-nuts] Advice on 10 MHz isolation/distribution (Clay)
lists at cq.nu
Thu Feb 11 18:19:02 UTC 2010
There's a quick and dirty phase noise to vibration spread sheet here:
You may want to plug in some numbers and see what you get. A lot is going to
depend on your oscillator's sensitivity, vibration isolation setup, and the
operational (as opposed to survival) vibration profile.
The added noise may take you into an area where a high speed op-amp based
design is quite adequate. Some topologies might also help with generating a
balanced output feed.
One downside to op amps would be power. Most of the circuits that have been
tossed around are already a bit outside the original budget you came up
with. That may or may not be significant in your case.
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of life speed
Sent: Thursday, February 11, 2010 1:05 PM
To: time-nuts at febo.com
Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
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
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.
Is your OCXO vibration isolated?
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.
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