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.

Note: The linearly polarized Gregorian receivers (1-2, 2-3, and 4-6 GHz) are oriented so that the X-channel is horizontal polarization and the Y-channel is vertical polarization on the sky.

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 1.15 - 1.73 21 9' 20 K 3.0
2-3 GHz 2.16 1.73 - 2.60 14 5.8' 22 K 6.0
4-6 GHz 4.90 3.95 - 5.85 * 6.1 2.5' 25 K 3.0
8-10 GHz 9.00 8.0 - 10.0 3.3 1.4' 27 K 3.0
12-15 GHz 13.70 12.0 - 15.4 2.2 54" 30 K 3.0 330"
Array 18-26 GHz 22.00 18 - 27.5 1.36 34" 35 K 6.8, 2.1 96"
## 18-22 GHz 20.00 18 - 22 1.5 37" 35 K 6.0 179"
## 22-26 GHz 24.20 22.0 - 26.5 1.2 30" 40 K 6.0 179"
26-40 GHz 34.00 26.0 - 40.0 0.88 22" 60 K 6.0 84"
40-52 GHz 46.00 41 - 48 0.65 16" 60-100 K 6.0 58"
80-100 GHz ("Mustang") 90.00 80 - 100 0.033 9" ?? n/a ~5"
## Note: Rcvr18_22 and Rcvr22-26 have been retired. Use the RcvrArray18_26 instead.
* Note: 4-6 Receiver may be used up to 6.18 GHz with degraded performance.

Click in the "Receiver" column for further information about each receiver.

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.

1-2 GHz Receiver (1.15 - 1.73 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 a cooled OMT producing linear polizations. The OMT has certain resonant frequencies creating spikes in the response that may show up as emission features, or absorption features on continuum sources. The approximate resonant frequencies are: 1255, 1439, 1598, and 1720 MHz. 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 bandpass 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 (1.73 - 2.60 GHz)

This receiver uses a cooled, HFET amplifier. It has one beam with dual polarizations. The feed is a corrugated horn with a cooled OMT producing linear polarizations. The OMT has certain resonant frequencies creating spikes in the response that may show up as emission features, or absorption features on continuum sources. The approximate resonant frequencies are: 1807, 2075, 2315, and 2520 MHz. The user can select circular polarization synthesized using a hybrid in the front-end. The user can select one of two RF bandpass filters: 1.68-2.65 GHz, 2.1-2.4 GHz. In addition, the receiver incorporates a notch filter which blocks 2.313 to 2.356 GHz, the digital radio satellites' (Sirius & XM) downlink bands. Calibration is by noise injection, with a choice between two levels.

Calibration data


4-6 GHz Receiver (3.95 - 5.95 GHz)

This receiver uses cooled HFET amplifiers. It has one beam, with dual polarizations. The feed is a corrugated horn with a cooled OMT producing linear polarizations, but the user can select circular polarization which is synthesized in a hybrid following the cryostat. The OMT has certain resonant frequencies creating spikes in the response that may show up as emission features, or absorption features on continuum sources. The approximate resonant frequencies are: 5150, 4700, 5220, and 5640 MHz. Note that although designed for operation from 3.95 to 5.85 GHz, the receiver has been measured to 6.18 GHz and may be usable to that frequency. Calibration is by noise injection, with a choice between two levels.

Calibration data


8-10 GHz Receiver (8.0-10.0 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 (12.0 - 15.4 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 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. The low-band channels exhibit evidence of polarizer resonances near the low end of the band, approximately 18.1, 18.5, and 18.7 GHz, and a weak resonance near 21.15 GHz. The high-band channels exhibit evidence of polarizer resonances near the low end, approximately 22.1, 22.4, 22.7 GHz, and a strong resonance at 25.8 GHz. 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 operating over 26-40 GHz. Each beam has one linear polarization perpendicular to the polarization in the other beam. Beam switching occurs before the first amplifiers at rates up to 10 kHz with dedicated back ends, allowing cancelling of receiver gain variations and 1/f noise. A dedicated continuum back end detects power in four sub bands with total coverage over the whole bandwidth. For spectral observing the signals undergo an inverting down conversion to 4-18 GHz, then through a millimeter 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 (41.0 - 48.0 GHz)

This receiver has two beams with fixed separation, each dual circular polarization. The two 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. Currently, useful frequency of operation is limited to 41-48 GHz; see support scientists for more details.

Calibration data