[back on-list] On Monday 06 June 2005 14:58, Marcus Leech wrote: > >As to the DBSRX, I mentioned to Charles Matt's statement of the 'less than > > 8dB noise figure' and Charles wasn't real impressed; need pretty good > > amplification ahead of it to get a useful noise temp. We have a few > > front ends with less than 3 dB NF here, and we will soon have better. No > > cryo here, yet.
> That's true of a lot of receivers, particularly wideband ones. What's > the noise figure of > the R8500? Probably in the same ballpark. Hmmm, about 6-8 dB I believe. But that's for 70 MHz IF reception; we have a good downconverter and LNA at the dish. > Add roughly 25dB of gain, with a N.F. better than about 0.6dB in front > of the > receive chain, and along with good spectral integration, you'll have a > pretty > good system. Yes, this is true. > I'm surprised that PARI doesn't have any of the better-quality LNAs for > 21cm-- > they're readily available and cheap. Both D.E.M. and R.A.S. make some > excellent LNAs at this frequency. The one on 26 West is a RAS LNA and feed; NF has been measured at 0.38dB. Our standard of comparison for 70MHz spectroscopy is a RAS SpectraCyber custom-built for us by RAS. We also have a rack mounted 1420-70MHz downconverter in the control room, but find it better to downconvert in the feedbox to 70MHz; there's 2,000 feet of 7/8's heliax in the line to contend with, and even 7/8's loss at 1420 isn't great. At 70 it's negligible. -- Lamar Owen Director of Information Technology Pisgah Astronomical Research Institute 1 PARI Drive Rosman, NC 28772 (828)862-5554 www.pari.edu _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
