Hi Mikhail, Good question!
I have some background with both devices you were asking about, I was
part of the design team for Vector Network Analyzers (VNAs) at HP
(8510B/C), and for Spectrum Analyzers at HP, Agilent, Keithley, and
National Instruments.
A VNA always has a built in signal source. The Spectrum Analyzer can be
equipped with a signal source by way of an optional tracking generator.
A VNA has dedicated hardware that allows it to directly measure it's
signal output level at the same time it measures a returning signal, and
it ratios the two measurements, so it's ratioed measurements tend to be
quite accurate. Those real-time source output level measurements
compensate for imperfect device match and other real-world realities
that can affect the output signal level. This extra hardware also adds
to it's cost. The VNA also has sophisticated calibration routines and
calibration devices that can further improve the measurement accuracy.
The Spectrum Analyzer tracking generator may or may not be calibrated
over frequency, and it's output level may not be measured as the
spectrum measurement is being made. The tracking generator output level
may also be affected by the signal match of the device under test. So
it's relative ratio measurement might not be as accurate.
These are the general cases for each type of instrument; depending on
the model a Spectrum Analyzer might have additional calibrations that
can make it's tracking generator more accurate.
Those differences aside, as Lee mentioned, either one will give you a
good enough answer for making a power system impedance measurement. The
accuracy needed for this measurement is met by either type of
instrument.
Hope this helps!
Chuck
Chuck Corley
National Instruments
On 2015-11-03 15:39, Lee Ritchey wrote:
They both give you the answer you need. The VNA is much more expensive------------------------------------------------------------------
and,
yes, it is more versatile if you need more than the SA does.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Orin Laney
Sent: Tuesday, November 3, 2015 2:06 PM
To: matusov@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: PDN impedance measurements
Spectrum analyzer + tracking generator is essentially an S21-only
scalar
network analyzer. The VNA is a more complete and versatile instrument.
Orin
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Mikhail Matusov
Sent: Tuesday, November 03, 2015 1:31 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] PDN impedance measurements
Hi gurus,
Please forgive my ignorance, but could someone enlighten me on what are
the
limitations of the PDN impedance measurement method using a spectrum
analyzer and tracking generator as described by Lee Ritchey in his
"Right
The First Time" book compared to using a VNA as described for example
in
Istvan Novak's "Frequency-Domain Power-Distribution Measurements - An
Overview" paper? I don't have practical experience with network
analyzers
but very familiar with the spectrum analyzers hence the question.
Thanks,
/Mikhail
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