Common Reference OSC for test equipment

[dnyberg2]

Can someone please explain to me what if any is the benefit in using one lab quality 10 MHz OSC to run all your bench equipment ref OSC inputs? And, what about this GPS thing? Why use an expensive GPS synced 10 Mhz OSC source to drive your test bench?

Thanks

 

[meBigGuy]

1 is Cheaper than buying ten?

Don't use GPS unless you need the accuracy?

Am I missing something?

 

[skeptic2]

At one time I wrote programs to test cellular phone circuit boards. One board had a 14 MHz oscillator that had to be tuned to +/-0.1 Hz. Using a frequency counter that meant tuning to within +/-1 Hz and then switching the frequency counter to 0.1 Hz precision which required 10 seconds per measurement to further tune to the 0.1 Hz requirement. Can you imagine how much time that took? This step was a real bottleneck in production.

Since all of our test equipment was tied to the same 10 MHz cesium reference, I was able to use a signal generator to mix the 14 MHz oscillator down to 300 Hz and use an audio analyzer to measure the 300 Hz. Audio analyzers use a different method to measure frequency than frequency counters. Audio analyzers count the number of 10 MHz cycles between zero crossings to calculate the frequency. The analyzer gave me a frequency reading accurate to 0.01 Hz, 300 times per second. This would have been impossible if both the signal generator and the audio analyzer hadn't been tied to the same reference.