GR connector

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Type RF coaxial connector
Designed Around the 1960s
Manufacturer General Radio
Cable Coaxial

The GR connector, officially the General Radio Type 874, was a type of RF connector used for connecting coaxial cable.[1] Designed by the General Radio Corporation, it was widely used on their electronic test equipment throughout the 60s and 70s.[2]

The connector had several desirable properties:

  • Good control of the electrical impedance across a wide range of frequencies
  • Reliable mating
  • Hermaphrodism, so there were no "male" or "female" connectors; any GR connector could mate with any other GR connector.[1]

This last characteristic was achieved by having both the inner and outer conductors made from four leaves, two of which were displaced slightly outwards and two of which were displaced slightly inwards. By rotating one connector by 90 degrees, its inner leaves would mate with the other connector's outer leaves and vice versa.

This connector was commonly found on GenRad brand RF test equipment. When frequently mated the inner leaves were susceptible to breakage due to stubbing, flexing and fatigue cracking as the connector was pressed together and alignment was perfected.

As can be seen in the photograph of a GR-900 to GR-874 adapter,[3] for a more secure connection the connector system has a locking mechanism consisting of an outer hex nut encasing a captured threaded barrel. The locking assembly is not captive and can be backed off the RF connector. The threaded barrel is supplied on each connector. The threaded barrel was withdrawn into the nut on one connector and extended on the other to allow the barrel to engage the nut of both mating connectors. This style of locking mechanism was continued in GR-874's thematic successors; the GR-900 precision 14mm connector that retains a crenelated hermaphroditic mechanical anti-spin feature to protect the sexless RF interface from rotating and galling when the locking mechanism is tightened, and the fully sexless APC-7 7 mm connector.

Adapters to other connector series were available.

Eventually, the limited frequency range of a 14mm connector and its high manufacturing cost overcame its ease of assembly and the GR-874 was supplanted generally by the 7mm type N connector and its variants the BNC connector and the TNC connector, and the later higher frequency 3.5mm SMA connectors. General Radio, then still a major source of RF test equipment, designed the incompatible GR-900 as a 14mm successor to the GR-874, filling the industry's need for a higher performance sexless connector for fully reversible lab standards and related test equipment. The GR-900 was in turn succeeded in this essential niche role by the completely sexless APC-7 connector.


  1. ^ a b "General Radio". Retrieved October 11, 2012. 
  2. ^ Thiessen, Arthur E. (1965). "A History of the General Radio Company 1915–1965" (pdf). West Concord, MA: General Radio Company. p. 61. Retrieved July 4, 2009. 
  3. ^