John Miles wrote:
Javier Herrero wrote:
Hello,
I will need to measure the phase noise of a 35MHz oscillator in the
range of 1 to 100Hz (well... and also at a higher range but this is no
problem), and I would like to know about the different alternatives. I
would like not to have to mess too much with mixers and soundcard
sampling, if possible :)
You probably need to find someone with an HP 3048A or similar outfit. A TSC
5125A will also do the job. The requirement to go below 100 Hz takes a lot
of the 'easy' solutions like the 11729C out of contention.
I think that the HP 5372A with opt 040 is able to do that, is this
right and worthy? If so, opt 040 is a pure software option or requires
also additional hardware? Would be possible also with a 5370A and
software processing of the raw data? Any other alternatives?
Thanks! Regards,
Javier
The 5372A or 5370A will only suffice if the phase noise is sufficiently
high.
They are likely to be too noisy by several orders of magnitude for a
good crystal oscillator.
That was my first thought as well, but the 5370 might be OK for measuring
TCXOs and the like. An HP paper from the mid-1970s suggests that it's
possible to reach ~-150 dBc/Hz at 1 Hz with contemporary hardware
(5345A-based, 2-ns resolution):
http://www.hparchive.com/seminar_notes/a-114.pdf
They mix down to a low IF before measurement, which they appear to vary in
order to get a lower floor at close-in offsets.
If nothing else, it should be possible to back the PN spectrum out of an
ADEV graph plotted with data from a counter, taking the noise slope into
consideration. It would take a lot of hacking (not to mention the effort
needed to get hundreds of measurements per second out of the counter, which
I also haven't looked into.)
There's a more user-friendly app note here:
http://www.ko4bb.com/Manuals/HP_Agilent/1%29_HP_App_Notes/HP_AN225_Measuring
_Phase_Noise_with_HP_5390A.pdf
Could be a reasonable way to measure PN at offsets below 10 or 100 Hz, at
least until the higher-order noise slopes invalidate some of the assumptions
baked into the software. It wouldn't scale very well to broadband offsets
in any event.
-- john, KE5FX
To take full advantage of the resolution of a 5370A it may be necessary
to use an external zero crossing detector to reduce the trigger noise to
a sufficiently low level with the relatively low beat frequency signal.
Bruce
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