[time-nuts] External Frequency Standard Inputs on Counters

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Apr 3 20:17:28 UTC 2009


Magnus

Another option (useful when the source amplitude is such that
terminating isn't an option and there isn't a suitable amplifier
available to boost the source amplitude) is to trim the cable lengths to
eliminate such standing wave nulls at the counter inputs.

Bruce


Magnus Danielson wrote:
> John Ackermann N8UR skrev:
>   
>> 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.
>>     
>
> Not terminating could create a null at or near one of them... thus 
> resulting in no input signal for that box. Overcoming that would require 
> more drive level than the other boxes wants...
>
> Cheers,
> Magnus
>
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