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P-18 “Spoon Rest D”

Description of the radar set, tactical-technical characteristics
P-18 in Greding 
(click to enlarge: 700·560px = 85 kByte)

Figure 1: P-18 in Greding

frequency: 150 … 170 MHz
pulse repetition time (PRT): 2.77 ms
pulse repetition frequency (PRF): 360 Hz
pulsewidth (τ): 6 µs
receive time: 2.4 ms
dead time: 377 µs
peak power: 160 … 260 kW
average power: 540 W
instrumented range: 200 NM
range resolution: ½ NM
hits per scan: > 15
antenna rotation: 6 … 30 s
(0 … 6 … 10 rpm.)

P-18 “Spoon Rest D”

The P-18 (Russian designators: 1RL131 Terek; Cyrillic: 1РЛ131 «Терек») is a relocatable radar set in the VHF range and is based on two all-terrain trucks (Ural) each with a two-axle trailer. It was mainly used in Eastern Europe and in the third world for target acquisition of missile launchers (Man-Pads: Strela, Igla). But it is also used as direct target acquisition for the missile complex «Wolchow» (aka SA-2 Guideline), coupled with a height finder mostly.

The transmitter consists of an approx. 2 m long coaxial cavity resonator with a planar triode of type GI-19B and feeds an antenna construction of 16 broadband Uda-Yagi antennas. A mechanical retuning system can retune this coaxial cavity resonator to four preset working frequencies. The automatic frequency readjustment is done to the more constant receiver frequency. The duplexer consists of gas discharge tubes and subsequent PIN diodes.

A sensitive transistorized HF preamplifier is connected between duplexer and the vacuum-tube-receiver used in the previous version (P-12) also. Moving target indication MTI (система селекции подвижных целeй СПЦ) is suppressed in the phase channel in two potentialoscopes (also adopted from the previous version), in whose a storage medium (Caesium) realizes a phase comparison between two pulse periods. With its complex azimuth-dependent wind compensation, this system can also be used successfully against chaff clouds. In the amplitude channel, these potentialoscopes are used to suppress non-synchronous pulse interference. By retrofitting with fast field-effect transistors as switches, this system becomes fully remote controllable.

Later versions, which weren't used in former GDR, were equipped with a digital MTI system, which is also offered internationally as a retrofit kit. The entire starting pulse generation, the block of potential memory tubes, and the compensation block are replaced by the new system. The radar sets used in the Republic of Hungary were completely modernized, with the entire reception section being replaced by modern digital reception technology from Hungarian production. The display is done on computer screens, and the entire system can be remotely controlled via an Ethernet connection. The software is based on the Windows 2000 operating system.

The basic version uses two PPI-scopes, one of which can be operated up to 500 m away with all remote control options. For maintenance purposes, there is also an A-Scope.

Except for the older MTI system and the large format cathode-ray tubes, the remaining signal path is transistorized.

The antenna control system is a servo-following system with various control inputs and can, therefore, rotate synchronously with other radar sets, which can then display the video of the P-18 in addition or instead of their own echo signal. Likewise, the evaluation of the foreign echoes can also take place in the P-18 or from its remote display.

P-18 is always fitted with secondary radar. This is, depending on the scope of delivery, a quite simply coded NRS-12 or a more complex system Parol. While the NRS-12 can still be loaded in the electronic container of the P-18, the Parol system requires an additional truck with a trailer.

The VHF range has the advantage over the other radar frequency bands that there are no anti-radar-missiles (missiles which react to the radiated frequency and are supposed to destroy the radar set) for this frequency range because an antenna with the necessary aperture angle for this range takes on very large geometric dimensions, which then can no longer be transported sensibly with air-to-ground missiles.

Furthermore, the diffraction of electromagnetic waves at the earth's surface is of greater importance than in other frequency ranges. The P-18 “looks” nearly 5 to 10% further “around the corner” than more powerful radar sets of higher frequency can do.

Picture gallery of P-18 “Spoon Rest D”
digitales SBZ

Figure 2: retrofit kit in use

Figure 3: Opened Coaxial Resonant Stub of the transmitter

Figure 4: PPI-scopes

Figure 5: modernized P-18 with compensation antennas on the lower mast for improved interference protection