Appendix: GBT Gregorian Receivers

The Gregorian receivers are mounted in a rotating turret in the receiver room located at the Gregorian Focus of the telescope. The turret has 8 portals for receiver boxes. All 8 receivers can be kept cold and active at all times. At present, the antenna must be moved to the access position (elevation = 77.67°) to rotate the turret. A future upgrade is planned that will allow the turret to be re-positioned at any elevation angle.

Basic information on each Gregorian receiver is summarized in the following table. Specifics on each receiver, including calibration data, follow the table.

Receiver Center f(GHz) Fsky (GHz) waveLen(cm) FWHM Tsys IF1 (GHz) Beam Separation
1-2 GHz 1.45 1.10 - 1.75 21 9' 20 K 3.0
2-3 GHz 2.16 1.72 - 2.74 14 5.8' 22 K 6.0
4-6 GHz 4.90 3.90 - 6.10 6.1 2.5' 25 K 3.0
8-10 GHz 9.00 7.70 - 11.60 3.3 1.4' 27 K 3.0
12-15 GHz 13.70 11.70 - 15.60 2.2 54" 30 K 3.0 330"
18-22 GHz 20.00 17.60 - 22.60 1.5 37" 35 K 6.0 179"
22-26 GHz 24.20 21.85 - 27.10 1.2 30" 40 K 6.0 179"
26-40 GHz 34.00 26.0 - 40.0 0.88 22" 60 K 6.0 78"
40-52 GHz 46.00 40.00 - 50.00 0.65 16" 60-100 K 6.0 58"

Click in the "Receiver" column for further information about each receiver.
Note that the high frequency receivers (26-40, 40-52) are not available in the summer season.

The nominal frequency range for each receiver is listed in the "Fsky" column. The choice of bandpass filters for each receiver, as listed below under the individual receivers, allows the nominal range to be exceeded slightly in some cases. The receiver performance may be considerably worse beyond the nominal frequency range, so please consult the calibration data before attemping to observe beyond the nominal range.

Note that the calibration data referenced from this page is out of date. Use the "rcvrCalibView" program to view recent data.

1-2 GHz Receiver (1.10 - 1.75 GHz)

This receiver uses a cooled HFET amplifier. It has one beam on the sky, with dual polarizations. The feed is a corrugated horn with cooled OMT producing linear polizations. The user can select circular polarization which is synthesized using a hybrid in the front-end. A polarization transfer switch allows polarization switching. The user can select one of four RF filters: 1.1-1.8 GHz, 1.1-1.45 GHz, 1.3-1.45 GHz, 1.6-1.75 GHz. The calibration is by noise injection, with a choice between two levels.

Calibration data

2-3 GHz Receiver (1.72 - 2.74 GHz)

This receiver uses a cooled, HFET amplifier. It has one beam with dual polarizations. The feed is a corrugated horn with cooled OMT producing linear polarizations. The user can select circular polarization synthesized using a hybrid in the front-end. The user can select one of two RF filters: 1.68-2.65 GHz, 2.1-2.4 GHz. Calibration is by noise injection, with a choice between two levels.

Calibration data


4-6 GHz Receiver (3.90 - 6.10 GHz)

This receiver uses a cooled, HFET amplifier. It has one beam, with dual polarizations. The feed is a corrugated horn with cooled OMT producing linear polarizations. The user can select circular polarization synthesized using a hybrid in the front-end. The user can select one of four RF filters: 3.9-5.9 GHz, 3.95-4.65 GHz, 4.55-5.25 GHz, 5.15-5.85 GHz. Calibration is by noise injection, with a choice between two levels.

Calibration data


8-10 GHz Receiver (7.9 - 11.6 GHz)

This receiver uses a cooled, HFET amplifier. It has one beam, with dual circular polarizations. The feed is a corrugated horn with cooled polarizer producing circular polarizations. The internal switching mode is frequency switching. The user can select IF Bandwidth of 500 or 2400 MHz. Calibration is by noise injection.
As of September 2004, the frequency range is extended up to 11.6 GHz. But users are cautioned that above 10 GHz, the polarization purity degrades, and the low cal drops off. One may prefer to use the high cal. Also watch out for a feed resonance at 11.45 GHz!

Calibration data


12-15 GHz Receiver (11.7 - 15.6 GHz)

This receiver has two beams on the sky separated 5.5 arcmin in azimuth, each with dual circular polarization. The feeds are corrugated horns with cooled polarizers producing circular polarizations. There is a transfer switch for feedhorn beam switching. The user can select IF Bandwidth of 500 or 3500 MHz. Calibration is by noise injection.

Calibration data

18-26 GHz Receiver (18.0 - 26.5 GHz)

This receiver has four beams total, each with dual circular polarization. One pair of beams cover the 18-22.4 GHz band with 3 arcmin separation in azimuth. Two other beams cover the 22-26.5 GHz frequency range, also with 3 arcmin separation in azimuth. The feeds are corrugated horns with cooled polarizers producing circular polarizations. Feedhorn beam switching is available. Calibration is by noise injection.

Calibration data


26-40 GHz Receiver (26.0 - 40.0 GHz)

This receiver has two beams separated by 84" in azimuth, each dual circular polarization operating over 26-40 GHz. Beam switching occurs before the first amplifiers at rates up to 2 kHz, allowing cancelling of receiver gain variations and 1/f noise. Continuum power detectors in the receiver detect power over the whole bandwidth. The signals following the first mixer go through the MM wave converter, with which one selects an IF band of up to 4 GHz in width from sky frequency ranges of 36.5-40 GHz, 30.5-36.5 GHz, or 26.0-30.5 GHz.

calibration data.


40-52 GHz Receiver (40.0 - 52.0 GHz)

This receiver has four beams with fixed separation, each dual circular polarization operating over 40-52 GHz. The four feeds are oriented parallel to azimuth with a separation of 58". The feeds are cooled corrugated horns with cooled polarizers producing circular polarizations. Feedhorn beam switching is available. The IF Bandwidth is 4000 MHz. Calibration is by noise injection and/or ambient load. A tertiary beam chopper is planned for this receiver.

Calibration data