[time-nuts] About HP10544A

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Mar 11 08:48:35 UTC 2009

Esa Heikkinen wrote:
> Bruce Griffiths wrote:
>> Attached circuit schematic illustrates how you could filter the harmonic
>> content of the 10544A below -50dBc.
> Ok that's something what I can't build from shelf parts anomore... What 
> kind of coils should be used here? The transformer may be tricky, I 
> think only way is to build it but first it's needed to find right kind 
> of core.

The inductors need to have a self resonance frequency (SRF) above 10MHz.
Try Farnell's EPCOS range (at least they specify the SRF).

The transformer is easy to do.
I used air core inductors but powdered iron toroids would suffice.

Just place a couple of windings on one core and adjust spacing turns,
etc until you get the required mutual inductance and then add an
additional inductor to the primary and secondary to pad out to the
required primary and secondary inductances. This is easier than trying
to wind on one air cored former and adjusting the spacings to achieve
critical coupling.

For 10MHz a #6 or #7 powdered iron core is appropriate.
Just choose cores with an appropriate A: with sufficient room for the
required number of windings.
I dont know how easy it is for you to get these.

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