I second Nithya here. I have been digging deep into the reflectometry measurements and cable reflection, cable loss as well as the backend input mismatch is going to be big issue. Accurate localisation of cable effect in both magnitude and phase is very difficult. So it is better to have one of such scale involved instead of multiple length scale.
On Tue, Apr 12, 2016 at 2:25 PM, DAVID DEBOER <[email protected]> wrote: > Let’s put this on the agenda for tomorrow. We could keep as is, except > put in 25m everywhere we can (so have 25m and 35m)… > > Dave > > On Apr 12, 2016, at 2:22 PM, Nithyanandan Thyagarajan < > [email protected]> wrote: > > Part of me favors having one cables of one kind (it this is an option) > than two - better to lose one mode than two besides other complexities > which we may not fully grasp yet that come with multiple cable lengths. > > From: <[email protected]> on behalf of DAVID DEBOER < > [email protected]> > Date: Tuesday, April 12, 2016 at 1:54 PM > To: danny jacobs <[email protected]> > Cc: hera <[email protected]> > Subject: Re: cable lengths > > I was going to suggest the same thing. We could have an ‘active’ long > cable (i.e. a pre-post-amp right at the balun). And how long do we need — > 150m is already uncomfortably long… > > On Apr 12, 2016, at 1:50 PM, danny jacobs <[email protected]> wrote: > > What about making most of them short and then some of them really long? > > On Tue, Apr 12, 2016 at 1:49 PM, Adam Beardsley < > [email protected]> wrote: > >> My concern would be pushing any cable reflection contamination to modes >> in the window. Currently only a small subset of MWA antennas have 150 meter >> cables, but the reflection line shows up very clearly. 45 meters puts the >> delay right at 0.2 h/Mpc, which is where we do a lot of our sensitivity >> forecasts. I doubt moving to 0.3 would change sensitivity much, but just >> food for thought. >> >> -Adam >> >> On Tue, Apr 12, 2016 at 1:26 PM danny jacobs <[email protected]> >> wrote: >> >>> The 35m length has been worrying me a little lately. Would there be any >>> downsides like having a different spectral response for the longer cables? >>> >>> ~D >>> >>> On Tue, Apr 12, 2016 at 1:24 PM, DAVID DEBOER <[email protected]> >>> wrote: >>> >>>> Hi - I was thinking about the analog cable lengths a bit. We have a >>>> spec at 35 m (30m+the vertical part to the feed). This puts the delay at >>>> about 0.15h/Mpc. Would it be advantageous to have, say, most of the cable >>>> lengths at 25m and a smaller subset at 45m? >>>> >>>> Dave >>>> >>> >>> >>> >>> -- >>> ================================================================ >>> Daniel C. Jacobs >>> KE7DHQ >>> 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/ >>> MWA: mwatelescope.org >>> HERA: reionization.org >>> PAPER: eor.berkeley.edu >>> >> > > > -- > ================================================================ > Daniel C. Jacobs > KE7DHQ > 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/ > MWA: mwatelescope.org > HERA: reionization.org > PAPER: eor.berkeley.edu > > > > -- To see a world in a grain of sand And a Heaven in a wild flower, Hold infinity in the palm of your hand And eternity in an hour
