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

[Bob Camp]

Hi

I really should learn how to read the whole message ....

==== 

Cancel the second request on vibe info.

-----

The gotcha with vibration isolation is that it will stop working at some
lower frequency. Aircraft have plenty of vibration running around at low
frequencies. 

That all sounds like bad news. Actually it's not. Since the phase noise
isn't going to be all that good below the cutoff of the isolation, the amp
doesn't need to sweat super low phase noise very close in. That can make the
choice of transistors easier.

Bob

-----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
amplifier(Clay)

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

Hi

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

Bob

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.

Bruce

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.

Clay

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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