Spec An for phase noise measurements
I decided to get a new spectrum analyzer rather than an 11729 at this
time. I bought an Advantest R3267 to replace the HP 8596E. It seems
to have phase noise performance in the same neighborhood as the
8560-series, for about half the price. In case I ever need anything
better, I can get an 11729 and use it with this analyzer, since it
goes down to 100 Hz, unlike the 8596 which only went to 9kHz.
I am seeing the following performance when measuring the built in 30
MHz reference:
100 Hz -81dBc
1 kHz -108 to -110
10 kHz -117
100 kHz -125
1 MHz -131
All of those are 3-8dB better than the spec, except for at 1 MHz where
the spec is -135. The measurements do jump around a bit.
I would really love to have PN.exe drive the analyzer so I can do real
phase noise plots. I have an electronic copy of the manual, which has
all the GPIB info, but the last time I dove into the PN code (in an
aborted attempt to port it to Linux), I had a very hard time grokking
the code, plus I don't have a Windows development environment. Is
there any way we can work together on getting this analyzer supported?
Several other Advantest machines are compatible with it, so any work
would cover multiple models.
Sure, send me the GPIB .PDF, either via Didier's site, ftp.ko4bb.com, user
manuals, password manuals) or via my GMail account at jmiles@gmail.com. It
looks like a great spectrum analyzer considering the prices they seem to
fetch on eBay. Should be a nice upgrade from the 8596E, all right.
The only requirement is that I need to be able to count on you to test the
code carefully. This can be a trying process, because PN.EXE has to carry
out a lot of interaction with the spectrum analyzer, and it's tough to write
code for one that isn't sitting on my workbench.
The ideal scenario is one where I have a remote-desktop account on a WinXP
box at your end, with an NI or Prologix board connected to the R3267. That
takes you out of my edit-compile-test loop. :) That's not vital, but it
really helps speed things up.
-- john, KE5FX
Are you using a noise marker that yields dBc/Hz values? The FFT window
function has its own required noise-response correction value, so if you're
just looking at a marker and doing the log10(RBW) subtraction yourself, that
could account for the difference.
Also, if there is a noise marker, check to see if it reads dBc/Hz or dBm/Hz.
Most of them read dBm/Hz values, which are obviously only equal to
conventional dBc/Hz values if you're measuring a 0-dBm carrier.
-- john, KE5FX
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com]On
Behalf Of Matt Ettus
Sent: Wednesday, January 23, 2008 4:08 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Spec An for phase noise measurements
I am seeing the following performance when measuring the built in 30
MHz reference:
100 Hz -81dBc
1 kHz -108 to -110
10 kHz -117
100 kHz -125
1 MHz -131
All of those are 3-8dB better than the spec, except for at 1 MHz where
the spec is -135. The measurements do jump around a bit.
If I change to "Digital mode for <100 Hz RBW", and turn on averaging,
I get much better results from the analyzer --
100 Hz -100dBc
1 kHz -110
10kHz -120
100kHz -129
1M -135
This, of course, makes me question all the measurements....
Matt
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Sure, send me the GPIB .PDF, either via Didier's site, ftp.ko4bb.com, user
manuals, password manuals) or via my GMail account at jmiles@gmail.com. It
looks like a great spectrum analyzer considering the prices they seem to
fetch on eBay. Should be a nice upgrade from the 8596E, all right.
Great! I sent the manuals to your email account. Loks like
everything GPIB is in chapter 5 of volume 1.
The only requirement is that I need to be able to count on you to test the
code carefully. This can be a trying process, because PN.EXE has to carry
out a lot of interaction with the spectrum analyzer, and it's tough to write
code for one that isn't sitting on my workbench.
I can do that.
The ideal scenario is one where I have a remote-desktop account on a WinXP
box at your end,
I can look into doing that, but I've never tried it before. I'm a
Linux guy, so point me in the direction you need...
with an NI or Prologix board connected to the R3267. That
takes you out of my edit-compile-test loop. :) That's not vital, but it
really helps speed things up.
I've got it hooked up on an NI GPIB-USB-B adapter.
Matt
On Jan 23, 2008 4:26 PM, John Miles jmiles@pop.net wrote:
Are you using a noise marker that yields dBc/Hz values? The FFT window
function has its own required noise-response correction value, so if you're
just looking at a marker and doing the log10(RBW) subtraction yourself, that
could account for the difference.
Also, if there is a noise marker, check to see if it reads dBc/Hz or dBm/Hz.
Most of them read dBm/Hz values, which are obviously only equal to
conventional dBc/Hz values if you're measuring a 0-dBm carrier.
I used the analyzer's phase noise function. It won't make a plot, but
will do measurements at a few spot offsets. It's not entirely clear
how it is calculating these, though.
Matt
Usually the built-in noise marker will average some nearby trace points
(behind the scenes), convert the result from dBm to dBm/Hz by subtracting
10*log(RBW), and add the filter/detector noise-equivalent-bandwidth
correction.
The latter factor makes the DUT look 2-4 dB worse than the 10*log(RBW)
calculation would indicate by itself. If it's not being applied by the
marker function you're using, that could explain why the results appear a
bit better than specified.
Similarly, if there are spurs present, or if the marker is positioned on or
near a steep slope in the trace, the averaging process can yield misleading
or inconsistent numbers.
-- john, KE5FX
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com]On
Behalf Of Matt Ettus
Sent: Wednesday, January 23, 2008 4:44 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Spec An for phase noise measurements
On Jan 23, 2008 4:26 PM, John Miles jmiles@pop.net wrote:
Are you using a noise marker that yields dBc/Hz values? The FFT window
function has its own required noise-response correction value,
so if you're
just looking at a marker and doing the log10(RBW) subtraction
yourself, that
could account for the difference.
Also, if there is a noise marker, check to see if it reads
dBc/Hz or dBm/Hz.
Most of them read dBm/Hz values, which are obviously only equal to
conventional dBc/Hz values if you're measuring a 0-dBm carrier.
I used the analyzer's phase noise function. It won't make a plot, but
will do measurements at a few spot offsets. It's not entirely clear
how it is calculating these, though.
Matt
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