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.edu>wrote: > 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 > ------------------------------------------------------- > > _______________________________________________ > psas-avionics mailing list > psas-avionics@lists.psas.pdx.edu > http://lists.psas.pdx.edu/mailman/listinfo/psas-avionics >
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