GBT Receiver Interface Information

This page is provided for outside groups interested in designing GBT receivers. Close consultation with the Green Bank Electronics staff is strongly encouraged, but general interface information is provided below.


Helium compressors on the GBT are located in a room on the alidade, are aircooled, and are capable of providing approximately 47 scfm of helium flow. Supply pressure is nominally 285 psi. Helium supply and return lines are equipped with Aeroquip self-sealing fittings (5400-S5-8). New receiver refrigerators should be sized to use the minimum helium flow necessary, as compressors typically supply more than one receiver.

Refrigerator power supplies compatible with CTI 1020, 350, and 22 models are provided.


Receiver vacuum roughing ports should be compatible with a Varian NW40 flange. A high-quality hand-operated vacuum valve should be provided on the receiver (Varian L6591302 or similar).

DC Voltages

Gregorian receiver power supplies are provided on the turret, supplying +15V at 10A; +5V, -15V, and +28V at 3A each. The power supply DC connector type is MS3102A-18-1S. Pinout is:

120VAC, 60Hz is supplied to Prime Focus receivers and is also available on the turret.


The Gregorian turret provides eight circular receiver mounting flanges at the roof of the Receiver Room. The secondary focal plane is located in the plane of the flanges, and standard turret stops place the focus at the center of the mounting flanges. Consult GB engineering if stops are required at other points. Details of the turret, receiver mounting, and the receiver room are available in drawings D35102A005, D35102M084, D35102M086, D35201M031, and D35102M032. Details of Prime Focus receiver mounting are available in drawing C35102M047. (Note that all these drawings are to scale, but most of them are in units of inches! The files were saved under Autocad version 2002 or earlier.)

Download Autocad files (zipped to 200KB).

PDF copies of the PF receiver mounting info and the standard front-end box are here.

A 3D drawing of the turret showing the L-band feed to scale is available in (zipped to 751KB).

A 3D drawing of the GBT Optics (units meters) is available in (Gbtoptics.dwg (70kB).

Elevation views of the GBT (side and front views) with major components labeled are available in (zipped to 585KB).

A 3D drawing of the entire GBT (all structural members!) is available in (zipped to 1.1MB).

Large equipment is transported to the tip of the feedarm by winching it to the base of the feedarm and placing it on a manlift with stops at the Receiver Room door and roof levels. The manlift can accommodate 6 ft. X 6 ft. X 8 ft. high equipment. During development, close consultations with NRAO engineers is encouraged to ensure new equipment can be safely handled and will fit correctly.

Local Oscillator

Two system LO sources located in the Receiver Room are Agilent 83620A synthesizers. The synthesizers' frequency range is 0.01-20.0 GHz with resolution of 1Hz. The LO is routed to the receivers thru an arrangement of microwave switches (the LO Router). Power delivered to a receiver depends on the frequency but in all cases is at least 0dBm. The synthesizers are locked to a 10MHz reference signal distributed from a hydrogen maser in the GBT Equipment Room to the Receiver Room via single-mode fiber. A round-trip phase monitor system allows measurement of delay changes over the LO Reference fiber.

Switching Signals

Two common TTL switching signals are distributed to Gregorian and Prime Focus receivers. These originate in one of several data acquisition backends located in the GBT Equipment Room, are transmitted to the Receiver Room on fiber, and are distributed to Gregorian receivers via coax with BNC connectors. They are distributed to Prime Focus receivers via multimode fiber. The switching signals are:

Some backends can generate additional switching signals which may be distributed to receivers. Consult GB Electronics.

Gregorian Plate Scale

The Gregorian plate scale and sign convention for the GBT pointing system (pdf)

This page last modified 4/20/2011. Maintained by: