Can one can get any cheaper than we have right now on PAPER? On Tue, Apr 12, 2016 at 2:45 PM, Chris Carilli <[email protected]> wrote:
> solution: buy cheap cables (ie. cable with a lot of intrinsic loss). > attenuation in the cable cuts down on the return loss dramatically (3 > passes down the cable from the FE instead of 1, and attenuation multiplies > exponentially. or something like that). > > you just have to crank up the power into the cable at the FE. or add some > gain at the receiverators. > > the VLA had a horrendous standing wave problem in the waveguide IF system > for years, until we put in attenuators. fixed. > > cc > > > > > > On 04/12/2016 03:32 PM, Aaron Michael Ewall-Wice wrote: > > I think it’s also worth considering that long cables may have > sub-reflections in them at delays smaller than the cable length due to > inhomogeneities in the dielectrics and bends. I think our reflectometry > measurements suggested that sub-reflections may be at the ~-50dB level > which could still be a problem for 21cm measurements. That said, we may > gain from the fact that these sorts of sub-reflections should be > uncorrelated between cables to different antenna elements. > > cheers, > > -Aaron > > > > > > On Apr 12, 2016, at 5:25 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]>[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]>[email protected]> > Date: Tuesday, April 12, 2016 at 1:54 PM > To: danny jacobs < <[email protected]>[email protected]> > Cc: hera < <[email protected]>[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]> > [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]>[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]> >> [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]> >>> [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/> >>> 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/> > 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
