[time-nuts] External Frequency Standard Inputs on Counters
bruce.griffiths at xtra.co.nz
Fri Apr 3 20:17:28 UTC 2009
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.
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
>> 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...
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