On Thu, Oct 25, 2018 at 4:46 PM Warin <61sundow...@gmail.com> wrote: > On 25/10/18 23:56, Paul Allen wrote: > > BTW, these days few radio telescopes are dishes. Most of them are phased > arrays and not on towers > or masts. > > > That depends on the frequency of operation. > > New dish reflecting ones are being build. They simply perform the best for > the intended frequencies. >
And there are dishes with phased arrays at the feed point, for beam forming, and phased arrays of dishes, for long-baseline interferometry. It all depends on what frequency, SNR, polarization and angular resolution you need. Paul is right that larger phased arrays are now practicable because of better electronics, giving dishes less of an advantage, but phased arrays are as old as radio astronomy. Jansky built his "merry-go-round" Bruce antenna (20.5 MHz) in 1932, while Reber didn't build his first dish until 1937. Jocelyn Bell discovered pulsars on a phased array built at Cambridge by Ryle and Hewish (which also produced the 3C catalog of radio sources - including 3C273, the first known quasar). The conclusion is either, "Life is full of tradeoffs," or "you really don't want to know!"
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