On 7/18/12 1:49 AM, Ian White GM3SEK wrote:
> A few points from this and earlier postings....
>
> 3. True Vector Network Analyzers that do offer - and indeed, require -
> OSL calibration at the exact location where the measurement is being
> made. The instrument then compensates for its own inaccuracies and
> presents the user with a much truer result. This is a defining feature
> of the true VNA that kicks it into a totally different league of
> accuracy.
>
> (For example, there is almost no difference in accuracy between the
> home-built N2PK VNA and a high-end laboratory VNA. The only significant
> differences are in extremely difficult measurements where it is highly
> likely that both analyzers are wrong.)
>
I would suggest that there is a significant difference between two
subflavors of the latter, depending on whether they used a tuned RF
detector or not. The TAPR VNA, for instance, has a broadband detector
scheme, so while it's great at measuring something like S21 of a filter,
if there's out of band interfering signals (e.g. measuring S21 between
two antennas), then there's a potential problem.
I think, also, that the lab VNA will probably have somewhat better
dynamic range than the less expensive kilobuck ones. For the vast
majority of uses (as you point out), whether you can accurately measure
the gain and phase of an S21 of -60dB is probably not a big deal. Most
of what you get with the lab box is better user interfaces, built in
computational features, and better remote control/export of data. I
don't think there's any LabView or Matlab drivers for the kilobuck class
VNAs.
The latter sort of thing is what you get when you spend the 10-20k for
the latest Agilent, R+S, or Anritsu portable boxes, which performance
wise are comparable to any of the tuned detector kilobuck boxes.
Oh yeah, you can also get an E-Cal widget for your Agilent, which is
pretty convenient. One could build such a thing pretty easily, though.
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