The AN/FPQ-6 is a fixed, land-based C-band radar system used for long-range, small-target tracking. The AN/FPQ-6 Instrumentation Radar located at the NASA Kennedy Space Center was the principal C-Band tracking radar system for Apollo program.

RCA’s Missile and Surface Radar Division developed the FPQ-6 skin tracking C-Band radar as a successor to the AN/FPS-16 radar set. The AN/FPQ-6 can provide continuous spherical coordinate information at ranges of 32,000 nautical miles (59,000 km ) with an accuracy of plus and minus 6 ft (1.8 m). The AN/FPS-16 has range limited to 500 nmi (930 km ) with an accuracy of 15 feet (5 m), although it could be modified to a maximum range of 5,000 nmi (9,300 km ).

Radar Ground Station Characteristics ------------------------------------ AN/FPS-16 AN/FPQ-6 --------- --------- Frequency band (MHz) . . 5400-5900 5400-5900 Peak power (MW) ...... 1.3 3.0 Antenna size (m) ........ 3.9 9.2 Antenna gain (dB) ...... 47 52 Receiver noise figure (dB) 6.5 8 Angle precision (units) . . . 0.15 0.1 Range precision (m)...... 4.5 3.0

The AN/FPQ-6 radar employed a 2.8 megawatt peak power (4.8 kilowatt average), broad banded (5400–5900 MHz) transmitter with a frequency stability of 1×108.

The 8.8 m diameter parabolic antenna, using a Cassegrain antenna feed, had a 0.4° beamwidth and a gain of 51 dB. Its monopulse, 5 horn feed system permitted the reference and error antenna patterns to have their gains independently established as well as the slope of the error patterns optimized while supplying target return signals to the receiving system with a minimum of insertion loss.

The three channel signal outputs of the antenna feed system were supplied directly to the receiving system without undergoing any additional loss-inducing signal manipulation with bandwidths optimized for the specified pulse widths of 0.5, 0.75, 1.0 and 2.4 microseconds and the receiver noise figure of 7.5 dB was improved to 3.5 dB through the addition of closed-cycle parametric RF amplifiers. This system ensured a dynamic range in excess of 120 dB.

The receiving system provided simultaneous presentation of the skin and beacon returns to the console operator so that skin tracking could be used if the beacon signal was lost.

The antenna pedestal was a high precision, two axis mount, using a hydrostatic bearing in azimuth and phase roller bearings in elevation to provide mobility and support to the counterbalanced, solid surface antenna. The antenna was positioned through anti-backlash dual drive pedestal gearing via a high torque-to-inertia electro-hydraulic valve motor system. A viscous coupler located between the valve motor and pedestal drive gearing damped out undesired mechanical resonances.

The AN/FPQ-6 had a self contained digital computer, an RCA FC-4101, whose primary purpose was to correct dynamic lag in the angular output data. As designed, both the AN/FPQ-6 and AN/TPQ-l8 radars were provided with a built-in data processor referred to as the RCA 4101 Computer.

The ground floor of the two story building contained the air-conditioning, transmitter heat exchanger controls, equipment load center data input junction box and ex-Mercury atomic time standard. The first floor contained the 8 equipment racks, the console, and the 3 megawatt transmitter.

Read more about AN/FPQ-6:  Functional Description, Some Notes On The AN-FPQ 6 Radar