are there dropouts or resonances at higher spectral resolution? what is
the resolution of the measurements?
thanks
chris
On 10/07/2015 09:25 AM, Eloy de Lera Acedo wrote:
Hi Danny,
We are looking into that requirement now. The 60 MHz ripple is due to
the nature of the LPDA antenna, it gives us very high sensitivity
across band at the expense of that ripple. It is important to keep in
mind though that this effect gets averaged out if you integrate the
whole field of view as it is a pattern dependent and we are talking
about a +/- 45 degrees FoV here.
Eloy.
On 7 Oct 2015, at 16:21, danny jacobs <[email protected]
<mailto:[email protected]>> wrote:
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] <mailto:[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] <mailto:[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 <http://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 <tel:%28%2B44%29%20%280%291223%20337563>
Email: [email protected] <mailto:[email protected]>
Webpage: http://eloydeleraacedo.weebly.com
<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/
--
*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] <mailto:[email protected]>
Webpage: http://eloydeleraacedo.weebly.com
