Introduction to School

1
Introduction to School

• Tomas E. Gergely
• Summer School on Spectrum
• Management and Radio Astronomy
• Green Bank, June 2002

2
Spectrum Management

• Radio Frequency Management Is Done by Experts
  Who Meld Years of Experience With a Curious Blend
  of Regulation, Electronics, Politics and Not a
  Little Bit of Larceny. They Justify Requirements,
  Horse-trade, Coerce, Bluff and Gamble With an
  Intuition That Cannot Be Taught Other Than by
  Long Experience
• Vice Admiral Jon L. Boyes
• U.S. Navy

3
The Green Bank Telescope and the NRQZ
The National Radio Quiet Zone (NRQZ) was
established by the Federal Communications
Commission (FCC) and by the Interdepartment
Radio Advisory Committee (IRAC) in 1958 to
minimize possible harmful interference to the
National Radio Astronomy Observatory (NRAO) in
Green Bank, WV and the radio receiving facilities
for the United States Navy in Sugar Grove, WV.
The NRQZ encloses a land area of approximately
13,000 square miles near the state border
between Virginia and West Virginia.
4
The VLA
The VLA consists of 27 antennas arranged in a
huge Y up to 36km (22 miles) across -- roughly
one and a half times the size of Washington, DC.
Pattern. Each antenna is 25 meters (81 feet) in
diameter their output is combined electronically
to give the resolution of an antenna 36km (22
miles) across, with the sensitivity of a dish 130
meters (422 feet) in diameter.
The resolution of the VLA is set by the size of
the array -- up to 36km (22 miles) across. At the
highest observing frequency (43GHz) this gives a
resolution of 0.04 arcseconds, sufficient to
see a golf ball held by a friend 150km (100
miles) away. The dishes can move on a track and
this allows the telescope to become the radio
equivalent of a zoom lens.
5
Arecibo Observatory
The huge "dish" is 305 m (1000 feet) in diameter,
167 feet deep, and covers an area of about twenty
acres. The surface is made of almost 40,000
perforated aluminum panels, each measuring about
3 feet by 6 feet, supported by a network of steel
cables strung across the underlying karst
sinkhole. It is a spherical (not parabolic)
reflector.
Suspended 450 feet above the reflector is the 900
ton platform. Similar in design to a bridge, it
hangs in midair on eighteen cables, strung from
three reinforced concrete towers. The combined
volume of reinforced concrete in all three towers
is 9,100 cubic yards. Each tower is back-guyed to
ground anchors with seven 3.25 inch diameter
steel bridge cables. Another system of cables
runs from each corner of the platform to large
concrete blocks under the reflector. They are
attached to giant jacks which allow adjustment of
each corner with millimeter precision.
6
Radio Telescopes of the World
7
INVESTMENT IN RADIO ASTRONOMY FACILITIES 1990-
Present and Planned

• USA
• GREEN BANK TELESCOPE (GBT) NRAO
  85 M
• ARECIBO (UPGRADE) NAIC
  22 M
• SUBMILLIMETER WAVELENGTH ARRAY (SWA) SAO
  62 M
• EVLA (Phase I) NRAO 50 M
• ALMA (US Contrb.) NRAO 330 M
• LARGE MILLIMETER TELESCOPE (LMT) U Mass 43 M
• CARMA U. Calif- CALTECH 15 M
• ALLEN TELESCOPE ARRAY (ATA) Berkeley-Private
  25 M
• SKA (Development) Consortium 1.5 M
• Total 169 464.5 M
  633.5 M
• Non-USA
• ALMA EUROPE 330 M
• LMT MEXICO 43 M
• GMRT INDIA 50 M?
• SARDINIA ITALY 60 M?