[time-nuts] About HP10544A

Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Mar 10 19:27:19 UTC 2009

Esa Heikkinen wrote:
> Hi Bruce...
>  > The required parts shouldn't be too expensive, however you may need
>  > to wind your own inductors for the series tuned LC circuits.
>  > Air core or powdered iron core inductors should be OK as long as you
>  > use shields between filter sections etc.
> Sounds like hard. How it's possible that lower grade ocxo's (like in 
> thunderbolt) output so much better spectrum? Is it all about ocxo output 
> driver circuit? Would it be easier to modify the 10544A itself than 
> trying to clean the distortion? Has anyone tried that kind of modification?

Attached circuit schematic illustrates how you could filter the harmonic
content of the 10544A below -50dBc.
If the output stage is elaborated somewhat its possible to get below
-60dBc or so.
Input stage is a simple cascode which has lower distortion that the 10544A.
The double tuned transformer has a primary inductance of 4uH, a
secondary inductance of 8uH and a coupling coefficient of 0.1.
The output stage consists of a common base stage plus a common collector
stage capable of driving an open circuit load, a 50 ohm load or a short
circuit load.
The output impedance of the output stage is nominally 50 ohms, its input
impedance is also nominally 50 ohms.

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