Dear Owen and Richard:
I have arrived at this set very late and the hour is late. However,
many, many years ago I was involved with the radio astronomy task of
measuring (always two major numbers involved) the flux from a strong source.
A reasonably predictable antenna gain was effected by using a very long horn
antenna with a rectangular (it might have been square) cross section. The
antenna was placed in a gully so that the source would pass through the beam
once a sidereal day.

The scheme used to construct the antenna was innovative and non-trivial.

A classic, comparison measurement was effected. Are not all
measurements comparisons? A dummy load was kept in ice water protected by a
condom. A switching scheme was used to switch between the dummy and the
antenna with an offset. I called it the HILLRAMS receiver. (High Isolation
Low Loss Radio Astronomy Microwave Switched Receiver)

Since the bandwidth was the same for both sources, once a day we
measured how much stronger the source was than the noise produced by a zero
centigrade source. All analog/

At Ohio State I did something similar with, probably for the first time,
actual digitizing that went to a computer (punched paper tape!). As I
recall, I did worry about sample rate, but it was much faster than any
changes being observed because a heavy LPF was used. (With the slow
computers in use, I needed not to overdesign the rate too much.) It seems
to me that if you have any reasonably fast filter fall-off, 11 kHz is plenty
fast enough. But then, I am not too sure that I understand your concern and
I am starting to ramble (though I am stone sober).

73 Mac N8TT


--
J. Mc Laughlin; Michigan U.S.A.
Home: