CPN-4 Radar
CPN-4 / MPN-11 GCA

This is a photo of the GCA, (Ground Controlled Approach), radar facility at Naval Air Station Alameda, California, circa 1978. Pictured here is the operators position. The orange face scope is the air search radar indicator which had a range of 200 miles. It's peak power was 600 kw. The air search radar was used to identify aircraft using a UPX-6 IFF, (Identification Friend or Foe), beacon decoder. It was also used to give radar vectors to pilots to guide their aircraft into the narrow beam of the precision radar. Above and to the right of the air search indicator are two GRC-171 UHF AM tranceivers used for communications.

The yellow scope below is the precision approach radar indicator. It had a range of 10 miles and had a peak power of 40 kw. Once the aircraft was identified on the precision radar scope, (photo below), the GCA controller would talk the pilot onto the center line by giving him heading changes. The GCA controller would also tell the pilot if he was above or below the glide slope.

The precision radar display, shown below, shows two different pieces of information. The top half, (two dashed lines), shows the 3.5 deg glide slope, (upper dashed line), extended to ten miles. The short vertical lines are mile markers.

Radar Display An aircraft blip can be seen below the second and third markers from the right edge of the screen. The bottom half of the screen shows the center line of the runway, single dashed line. The very brights objects to the far left of the screen is ground return clutter.

The all tube, CPN-4 / MPN-11 GCA, radar was used at Naval Air Station Alameda until about 1985. The FPN-63, all solid state, GCA radar was then used until NAS Alameda, Nimitz Field, was closed on June 30, 1996.



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