[time-nuts] External Frequency Standard Inputs on Counters

[Bruce Griffiths]

Hej Magnus

I wasn't recommending this method for anything but a possible solution
when no other method was feasible.
Of course the other solution is to use a sufficiently short total cable
length.
The only questions are:
How short ?
How does the counter reference input impedance (R and C) affect the
maximum total cable length?

Daisy chaining via the reference output signal provided by some counters
will increase the noise of the reference for counters further along the
chain.
The significance of this depends on the application and the performance
of the reference frequency buffers inside the counters.

Using a high performance distribution amplifier reduces interaction
between counters and the potential degradation due to each counter's
reference output buffer.

Bruce

Magnus Danielson wrote:
> Bruce Griffiths skrev:
>   
>> 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.
>>     
>
> Certainly, but consider the frequency of 10 MHz, 100 ns. 1 ns is 2 dm 
> one-way, so a full-wave is 20 m, a half-wave is 10 m and a quarter-wave 
> is 5 m. It is certainly possible, but a lot of cable.
>
>   
Thats true only for cable like RG58 with a solid PE dielectric.
For cables having gas injected PE or PTFE foam dielectric the
corresponding lengths are a little greater.
> I'd think this is when I would recommend tossing a distribution 
> amplifier on it or rely on the outputs to form chains that way.
>
> Cheers,
> Magnus
>
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