VLBA antennas are capable of observing at ten different wavelengths. The feeds are sized according to the length of the wave being reflected into them. The sizes available on these antennas, along with the frequency of the wave observed are:
Photo of apertures on feedcone
Wavelength
Frequency
90 cm*
327 MHz
50 cm*
610 MHz
20 cm
1.5 GHz
13 cm
2.3 GHz
6 cm
4.8 GHz
4 cm
8.4 GHz
2 cm
14 GHz
1.3 cm
23 GHz
7 mm
43 GHz
3 mm
86 GHz
 
 
*In the middle of the subreflector is a dipole antenna for observing at 90 cm and 50 cm. The wave bounces from the dish directly to this UHF antenna. Photo of the diple antenna
Photo of apertures with heating elements On the feed housing small heating elements focus on the apertures to prevent the formation of ice crystals. St. Croix is the only antenna that does not have heaters.
Using this special setup of dichroic and ellipsoid, the antenna can observe at two frequencies simultaneously. The dichroic allows 13cm waves to pass through to the 13cm aperture, while the remainder of the waves are reflected to the ellipsoid (which is retracted in this photo). The ellipsoid, in turn, bounces the 4cm waves into the 4cm aperture. Photo of dichroic and ellipsoid
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Modified on Friday, 26-Sep-2008 12:15:34 MDT