[time-nuts] External Frequency Standard Inputs on Counters

John Ackermann N8UR jra at febo.com
Fri Apr 3 12:07:52 UTC 2009


I think you guessed it, Ed.  There are a number of applications where 
you want to drive at least two devices from the same reference so using 
a moderate input impedance facilitates that.

I've done some goofy things like trying to drive 3 or more 5334A 
counters or 3586C VLF receivers from a single reference.  My feeling as 
a result is that you can safely daisychain two devices, but three may be 
tricky.

Ideally, you should terminate the end of the chain with 50 ohms, but 
depending on the drive level you might not be able to get away with that.

John
----

Ed Palmer wrote:
> I see that on many counters (e.g. SR620, HP 5370, HP 5372) the external 
> frequency standard input has an impedance of 1Kohm.  Why such a high 
> value?  Are they implying that it's acceptable to daisy-chain a single 
> reference to multiple devices like an old 10Base2 ethernet network?  
> Should such a link be terminated in 50 ohms like a 10Base2 network?
> 
> Ed
> 
> 
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