[time-nuts] Fast frequency counting question

Henk ten Pierick henk at deriesp.demon.nl
Sun May 4 16:08:49 EDT 2008


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  


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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