[time-nuts] Fast frequency counting question
Henk ten Pierick
henk at deriesp.demon.nl
Sun May 4 20:08:49 UTC 2008
Hi,
My first choice would be the HP533130A. The HP533130A is a
interpolating counter with a scope-like display. It has the
resolution you need. The resolution is determined by the time/div
setting and the vertical scale. It divides the horizontal display
time in 250 or 450 time slots, depending on time or frequency
measurements. In a slot, the first sampled edge is timed, the rest
counted. edge timing is done as 5370 and 53131/2. Sampling can be set
manual or automatic. If you understand the working principle, it is a
fantastic instrument. If time/div is to long you are losing
bandwidth, if it is to short noise increases. Read the manual. The
reference is very clean. Also available is the HP53305 software via
gpib.
Henk
On May 4, 2008, at 21:16, Murray Greenman wrote:
> Hi all,
>
> We have a problem at work where one of our engineers needs to measure
> the start-up chirp in an oscillator destined for a GPS application.
>
> We are looking for ppb level frequency resolution with sample periods
> around 10 - 20us (yes, that's us, not ms!). The chirp is all over well
> inside 1ms.
>
> The measurement is on a 40MHz oscillator, which is mixed down to about
> 198kHz to improve resolution. We can count the down-converted
> frequency
> in a conventional manner with no problem. The problem is of course
> that
> at 198kHz the period is ~5us so even an interpolating counter will
> struggle.
>
> Preliminary tests with a Pendulum CNT90 counter give results that
> deviate +/- 16Hz when the gate time is reduced to 10us. We are using
> GPIB to capture multiple repeated samples, and trigger the counter
> when
> the oscillator is powered up. We also have an Agilent 53181A counter
> available.
>
> Any suggestions (a) how to make the measurement; (b) what is
> causing the
> counter result to degrade in this way?
>
> Thanks,
> Murray Greenman ZL1BPU
>
>
>
>
>
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