Between test setups, Glenn gave an excellent explanation
of Smith charts (part of the VNA results), then
we found a nice poster tacked up on a wall, which we liked.
I found a copy (pdf) of the poster on Agilent's site:
http://cp.literature.agilent.com/litweb/pdf/5989-6924EN.pdf
Watching the results change on the VNA as Glenn alternated
between placing his hands on the Al shell of the rocket below
the antennas and letting go was a dramatic demonstration
of how easy it was to affect the results. In this case, by changing
the (effective?) dielectric constant of the antenna system.
(Longer, more accurate explanations may be available.)
As it turned out the VNA results were consistent with measurements
at a PSU lab with a different VNA, in what was assumed to be a higher RFI
environment.
--
Side note:
Spectrum analyzer parameter VBW (video bandwidth) is a factor combined
with RBW to determine sweep time and is used to reduce noise. RBW
(resolution
bandwidth) 'is the minimum bandwidth over which you can separate
two signals and still see them.' (ref: Agilent). So, RBW is
what we thought it was.
More info on spectrum analyzers:
http://cp.literature.agilent.com/litweb/pdf/5952-0292.pdf
-K
On Sat, Aug 13, 2011 at 1:34 PM, Andrew Greenberg and...@psas.pdx.eduwrote:
Hi everyone!
We tested our antennas at NW EMC on Friday morning; it went very well.
http://psas.pdx.edu/news/2011-08-12/
The first thing we found is that our antennas are all about 3% too low
on resonant frequency. Not terrible, but much worse than the 0.1% we
were aiming for. This is probably due to the new UHMW PE batch that we
have. Now we know.
Propagation wasn't as good as the last batch: we're about -4 to -5 dBi,
which is about the same amount below the last batch. We think this is
some kind of mistake in our new CPA design, which we'll investigate and
try to fix before our launches in 2012.
So: they do work, just not great :)
Glenn, Jen, Nathan, K: please feel free to add comments.
Andrew
--
---
Andrew Greenberg
Portland State Aerospace Society (http://psas.pdx.edu/)
and...@psas.pdx.edu P: 503.788.1343 C: 503.708.7711
---
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