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

Bob Camp lists at cq.nu
Thu Feb 11 17:38:58 UTC 2010


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?



-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of life speed
Sent: Thursday, February 11, 2010 12:27 PM
To: time-nuts at febo.com
Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution

Message: 2
Date: Thu, 11 Feb 2010 07:54:40 -0500
From: Bob Camp <lists at cq.nu>


Implementing that circuit without using a hybrid would be a bit of a


Message: 6
Date: Fri, 12 Feb 2010 04:09:08 +1300
From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>

Yes implementing an exact copy without using a hybrid would be difficult.
However for 10MHz use, its probably not too difficult since that 
isolation amplifier is intended for a 100MHz signal and the requirement 
is for 10MHz operation.

If the transistor ft's are reduced by a factor of 10 or so it shouldn't 
be too much of a problem.
At 10MHz 2N3906 and 2N3904 transistors should suffice.


Hi Bruce,

Thanks for the tips.  I've been trying to follow the circuits you posted. 
The first one, in .PNG format, looks like a common-base complementary
(push-pull) stage followed by a common-emitter complementary stage to
provide the low impedance output.

The second circut in .GIF fromat I am having a bit more trouble
understanding.  I see that V6, 7 are at the outputs and just used for to
simulate isolation.  V1 is the input? Are Q5,6 used to set the bias point of
Q4?  Are V2,3,4 just there to bias the transistors for simulation purposes,
and this would be accomplished another way in a real implementation?

Please explain the comment regarding the hybrid.  Are you and Bob referring
to a 90 degree hybrid coupler, or other quadrature method like a
transmission line transformer?  What would be the purpose of such a device?

Would it be too much to ask for a description of these circuits?  I suppose
we all have our areas of expertise, and transistor isolation amps are
somewhat new to me.

Thanks again for all the help.


PS - yes, the OCXO is vibe isolated.  And you are certainly correct about
long runs of single-ended coax being susceptible to noise.  The system
designer has accepted this and allowed for some degradation.  But I will
look into the practicality of implementing a differential line for the long
run of 10 MHz cable.  However, I will still need to implement traditional
coaxial isolated 10 MHz outputs.


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