[time-nuts] Another David Partridge frequency divider question

Chris Wilson chris at chriswilson.tv
Thu May 9 14:42:56 EDT 2013

> Azelio wrote:

>>Usually the external reference input of measuring equipment is
>>internally squared, so if you feed a square or sine wave there should
>>be no difference.

> Some external reference inputs may be DC coupled and zero-switching, 
> in which case unipolar logic levels will not work well.  I don't know 
> of any specific equipment to which this may apply, but if you try it 
> and it doesn't work well it is one thing to consider.  An external 
> coupling cap (or AC coupling the output internal to divider) should fix it.

> Also, 74AC logic level (~ 5 Vpp) may be a little hot for some 
> reference inputs.  Many reference inputs present a load impedance 
> higher than 50 ohms to the source (often ~ 1k ohm), so you may not 
> get the divide-by-2 attenuation from the open-circuit voltage that 
> you expect in a matched system.  In this case, an external 50 ohm 
> termination will reduce the level to ~ 2.5 Vpp.

> Best regards,

> Charles

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09/05/2013 19:42

Charles, Azelio. Many thanks, just what I needed, I am glad I asked,
info noted, all the best gentlemen!

       Best Regards,
                   Chris Wilson.

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