Radars

AN/SPS-43A

The AN/SPS-43A radar used a 41 foot wide AS-1092/SP "bedspring" antenna for long range air search, capable of detecting airborne targets out to a range of 300 miles. The antenna had a radiation pattern with a 7° horizontal and 20° vertical beam width. It operated in the VHF band at 200 MHz with 180 kW peak output.

The shorter antenna at the top is an AT-352/UPA-22 IFF Interrogator antenna. Friendly aircraft and ships carried an IFF (Identification Friend or Foe) transponder that responded to an interrogation signal from the ship. The encrypted code identified the unit - no code meant the target might not be friendly (or the IFF transponder wasn't working). During the Vietnam War the ship also carried a Top Secret Soviet IFF Interrogator that would cause enemy units to identify themselves. It was very useful for sorting out friendly and enemy aircraft over North Vietnam.

AN/SPS-43 antenna AN/SPS_43 antenna AN/SPS-43 antenna

The antenna was a double corner reflector with a "W" shape in cross section. It had an array of ten pairs of dipoles fed by a complex coaxial transmission line system with power dividers to feed each pair of dipoles.

AN/SPS-43 radar antenna AN/SPS-43 antenna waveguides

The antenna attached to a rotating turntable that rested on a pedestal. The pedestal sat on an elevated support base that also supported the drive motor.

SPS-43 antenna base SPS-43 antenna base

AN/SPS-30

I had very little to work with to make the AN/SPS-30 air search and altitude finder radar antenna. I made this model from a few medium resolution photos. Someday I hope to find blueprints so I can make a more accurate model. I have obtained some close up photos of the antenna on the USS Little Rock so I can add more accurate detail to the model. It's on my "to do" list.

An AS-791/UPA-43 IFF Interrogator antenna located on the same platform was slaved to the SPS-30.

AN/SPS-30 height finding radar AN/SPS-30 height finding radar

AN/SPS-10A

The AN/SPS-10A was the ship's main surface search radar, and it also had a limited low altitude air search capability. This model was created from dimensioned drawings in NAVSHIPS 0967-156-3040 Technical Manual for Antenna Assemblies AS-936( )/SPS-10B, and is fairly accurate. Additional details were taken from photos of the AN/SPS-10 on the USS Sullivans at the Buffalo and Erie Naval Park.

AN/SPS-10 radar antenna AN/SPS-10 radar antenna AN/SPS-10 radar antenna AN/SPS-10 radar antenna

The antenna assembly consisted of a base gearbox and motor, the rotating "spider" which held the feedhorn assembly and supported the reflector. The reflector had a tubular framework that supported many "slats" that formed the reflector surface. A second tubular framework on the back of the reflector supported it and attached it to the spider.

AN/SPS-10 radar antenna AN/SPS-10 spider AN/SPS-10 reflector
AN/SPS-10 reflector and spider AN/SPS-10 reflector and spider AN/SPS-10 reflector and spider

The SPS-10 rotated clockwise at 15 RPM. The radiated beam was 16° high and 1.5° wide. The radar operated at 5.42 to 5.825 GHz with a 285 kW peak power. The antenna also carried an IFF dipole.


Pathfinder radar

Pathfinder

The ship also had a small Pathfinder radar that was used for navigation. It was used mainly by the bridge watch to obtain radar bearing and range "fixes" for determining the ship's position in channels and harbors. The radar was mounted on the front of a light mast positioned on the O4 level just above the bridge. This mast also carried navigation lights and antennas.

This is another "photoguestimation" model. I have found no really good photos and the radar unit has been removed from the USS Little Rock so I do not have a sample to measure. I don't even know the manufacturer or model number. Any information would be appreciated.


Directors

Mk 37

The Mk 37 director was used to control direct line of sight gunfire from both the triple 6"/47 turret and the dual 5"/38 gun mount. It carried both optical and radar systems to determine range, bearing and elevation to the target. The AN/SPG-25 radar antenna was slaved to the optical range finder sights extending from the sides of the director. Both were controlled by a stable element to adjust the angle to maintain these components horizontal (parallel with the water surface) as the ship rolled.

Four or five personnel were crammed into the director for gunfire missions. The Director Officer sat on a seat under the black folding hood. He had a set of binoculars that were slaved to the sights and a trigger for direct fire control of the guns. This was the highest manned position on the ship and the best seat in the house for observing the show! Two operators inside the front of the director operated the range and elevation equipment. Another man at the rear operated the optical sights, and a radar operator in the rear operated the radar equipment. Access to the director was via a ladder inside the barbette or the ladder rungs and rings welded to the outside of the barbette. Either way it was interesting when the ship was rolling and the director was rotating.

I found a dimensioned drawing of a Mk-37 gunfire director to use for the basic structure. I took a lot of photos of the director on the USS Little Rock and they were useful for details. This is a pretty accurate model.

Mk 37 director Mk 37 director Mk 37 director Mk 37 director Mk 37 director

AN/SPG-49

I worked from photos and sketches to create this model of the AN/SPG-49 missile tracking radar. During a visit to the USS Little Rock museum ship I took lots of pictures and I made some drawings with dimensions taken from the directors. The dimensions of this model should be accurate to within a few percent.

AN/SPG-49 AN/SPG-49 AN/SPG-49 AN/SPG-49

This thing was a monster by any definition. It was as tall as a two story house and gimballed to rotate around three axes. The 3 to 5 megawatt radar transmitters were located inside the antenna itself instead of inside the deck house as was common in other tracking antennas. The antenna was jammed full of electronic equipment, electric motors and hydraulic equipment. On top was a Mk12 television camera with a Mk7 telescopic lens for tracking targets visually.

AN/SPG-49 base AN/SPG-49 yoke AN/SPG-49 gimbal AN/SPG-49 antenna

The entire antenna assembly rotated on the conical base around the vertical axis for coarse training in bearing. The square tubular gimbal rotated around the horizontal axis for training in elevation, supported by the "U" shaped yoke. The antenna itself rotated around the vertical relative to the gimbal for fine bearing adjustments.

AN/SPG-49 AN/SPG-49 AN/SPG-49 AN/SPG-49

The large motor attached to the base turned the yoke. Two motor assemblies attached to the yoke at the rear drove the large "C" shaped gear on the gimbal. Four motors rotated the antenna, two on a platform at the top of the gimbal and another pair on a platform at the bottom. The antenna contained a cooling system with a pump to circulate the coolant and a large radiator with a fan to remove heat.


AN/SPW-2

The AN/SPW-2 missile guidance transmitter model was based on photos of a unit on the USS Little Rock, plus several detailed and dimensioned sketches. It is a pretty accurate model.

SPW-2 SPW-2 SPW-2 SPW-2

The upper "U" frame rotated around the vertical axis on the cylindrical base. The antenna was mounted on an assembly that rotated around the horizontal axis, supported on the "U" frame. The feeder cone in the center of the antenna dish rotated 30 times per second. It rotated slightly off center to produce a conical beam. Behind the antenna reflector is a small optical telescope used for aligning the antenna. The telescope peeks through a hole in the reflector dish.


Mk 23 Mod 0 Target Designation Transmitter

The ship had two Target Designation Transmitters (TDT) on the O5 level, port and starboard, just forward of the Mk 37 director barbette. This was the Forward Air Defense station. These were relics from the WWII era, and were pretty much obsolete in the age of jet aircraft and missiles. I don't know if they were ever manned.

Binoculars were mounted on the TDT arm. The operator rotated the TDT about the vertical axis and raised the arm around the horizontal axis to place the target in the field of view. Then he pressed a button on the hand grip to send bearing and elevation data to the ship's gunfire control system. The gun control computer could then slew the Mk 37 director to the bearing and elevation to track the target.

TDT TDT TDT TDT

Miscellaneous

What is a "dixie cup?"

Thanks to Richard Merriman for the SPS-10 Technical Manual information.

Thanks to Art Tilley for photos of the TDTs on the USS Little Rock CG-4 museum ship.