874-LBA

The General Radio 874-LBA Slotted Line was introduced in Catalog O (1956) and remained available through Catalog S (1965). Its function is to observe the electric field along the inside of a coaxial transmission line using a carriage-mounted probe moving along the line.

By observing minima and maxima of a standing-wave pattern, parameters like frequency, standing-wave ratio, or impedance can be measured, and thereby the characteristics of a circuit connected to the load side of the line can be determined. Applications include analysis of antennas, components, coaxial elements, and networks.

The 874-LBA is an update of the 874-LB, featuring improved accuracy and carriage construction. The redesigned carriage is controlled by a nylon cord forming a complete loop, and a series of pulleys to remove its drive control to a fixed position at the load end. This reduces changes in probe coupling caused by changing forces on the carriage. An optional 874-LV Micrometer Vernier can be attached for high-resolution measurements.

The 874-LBA was supplied with a protective wooden case, a spare nylon cable, and a crystal detector.

Specifications

• Characteristic Impedance: 50 Ω, ±0.5%
• Scale Accuracy: ±(0.1 mm +0.05%)
• Frequency Range: 300 MHz to 5 GHz; for measurements below 300 MHz, add 874-L30 air line sections
• Length: 50 cm probe travel (λ/2 @ 300 MHz, λ/4 @ 150 MHz)
• Constancy of Probe Penetration: ±1½%
• Residual SWR: 1.025 @ 1 GHz, 1.07 @ 4 GHz

Links

• Experimenter December 1954 describing Type 874-LBA
• 1N23B Microwave Diode Data
• Handbook of Coaxial Microwave Measurements
• AT&T Archives Wave Machine Tutorial @ YouTube
• Predecessor: 874-LB
• Successor: 874-LBB (8.5 GHz)

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