Hi Eloy, Is there a goal in mind for the flatness of the passband? At the moment it looks fairly dominated by the ~60MHz (16ns) ripple but its kind of hard to tell if there is faster stuff in there at a smaller level.
Cheers, ~Danny On Wed, Oct 7, 2015 at 7:50 AM, Eloy de Lera Acedo <[email protected]> wrote: > Hi John, > > Do you mean the feature at 100 MHz? That one is not predicted by the > modeling and indeed it is very strange because it does not show up in the > other polarisation. We will check with our Australian colleagues, see what > they think. That should not be there. > > The reason why the A/T measurements give larger values than the model can > be related to this: > > "For Hydra A, our model predicts the flux density at 300 MHz to be ∼1/3 > that at 74 MHz. However, detailed measurements specifically targeting Hydra > A at 74 and 330 MHz [35] show that the flux density of the compact central > region reduces less steeply with frequency, and would be only ∼1/2 that > at 74 MHz. Unlike the surrounding diffuse emission, the compact central > region is not spatially filtered at the higher frequencies, thus our > modelled "known" flux density causes an underestimate of the actual flux > density, resulting in a higher than actual A/T . In future processing of > measurement, we expect significant convergence as the models of calibrator > sources are improved for the MWA and other wide-band low-frequency > telescopes." > Regarding A/T, in this paper (Fig. 15) you have our best estimates for A/T > calculation for SKA before re-baselining (before halving the number of > elements). > > http://rd.springer.com/article/10.1007/s10686-015-9439-0 > > Cheers, > Eloy. > > On 7 Oct 2015, at 15:31, Jonathan Pober <[email protected]> wrote: > > I'm not used to thinking about A/T this early in the morning, but are > Figures 14 and 15 what we've always wanted to see from the SKA? Measured > (and simulated) frequency responses? > > http://arxiv.org/abs/1510.01515 > > (There seems to be a prevalance of 15's here, which numerology.com tells > me corresponds to "Loving, forgiving, tolerant" -- for those of you perhaps > looking for guidance in your relation to the SKA.) > > In Figure 14 there are a few sharp features beyond what the model > predicts. I need to read the paper in more detail to figure out exactly > what the measurement is. Those could be due to sidelobes from other > sources affecting their spatial filter, although they are using the full > 128 tiles of the MWA for cross correlation, so the PSF should be good. > They're also stitching together the band from several 30.72 MHz chunks, so > those could be artifacts at band edges. > > Maybe Eloy and/or Nima have some thoughts on these results? Very nice to > see this work taking place and moving ahead. > > Cheers, > > Jonnie > > > -- > *Dr. Eloy de Lera Acedo* > > *Senior Research Associate* > Astrophysics Group > Cavendish Laboratory > University of Cambridge > JJ Thomson Avenue > Cambridge CB3 0HE > > *Teaching Associate and Bye-Fellow* > Downing College > Regent Street > Cambridge CB2 1DQ > > Telephone: (+44) (0)1223 (3)37365 > Fax: (+44) (0)1223 337563 > Email: [email protected] > Webpage: http://eloydeleraacedo.weebly.com > > -- National Science Foundation Fellow Arizona State University School of Earth and Space Exploration Low Frequency Cosmology Phone: (505) 500 4521 Homepage: http://loco.lab.asu.edu/danny_jacobs/
