[time-nuts] Another David Partridge frequency divider question
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,
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Charles, Azelio. Many thanks, just what I needed, I am glad I asked,
info noted, all the best gentlemen!
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