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P-722: Rohde & Schwarz NP 4

Large base VHF direction finding system P-722, Rohde & Schwarz NP 4; manufactured by Rohde & Schwarz, Munich.

From the Large base Doppler direction finder Rohde & Schwarz NP 4, the Swiss Air Forces acquired seven units in 1962. The systems were used as a VHF aeronautical direction finder at the Emmen, Dübendorf and Payerne military airfields and at three mountain sites.

P-722: Rohde & Schwarz NP-4

Technical data

Power supply

  • Mains operation]]: 220 V AC mains supply

Dimensions

Accessories

  • DF bearing display NA 403/3
  • Demodulator NA 406/2, reference phase field NV 407 (distribution of the various signals to daughter bearing displays)
  • NA 401 DF antenna: Adcock antenna with 29 dipoles mounted in a circle with a diameter of 4.5 m

P-722: Rohde & Schwarz NP-4

System material

The system consists of the VHF receiver (aircraft radio receiver) NE1/21E, the power supply unit NE1/21N, the demodulator NA 406/2, the reference phase array NV 407 and the direction finder NA 403/3 as well as the direction finding antenna NA 401.

The VHF aeronautical radio receiver NE1 covers the aeronautical radio range at 100 - 156 MHz and has an analogue dial with a conventional tuning knob.

The determined azimuth angle is automatically set on the NA 403 direction finder.

Technical principle

Block diagram of VHF receiver NE1
NE1 direction finder receiver: The antenna signal from the DF antenna passes through a bandpass 100 - 156 MHz to an RF stage V1, in the mixing stage V2 the signal is converted to the first IF of 10.7 MHz. The oscillator V3 can either be tuned between 110.7 - 166.7 MHz or it can be crystal-controlled. Thanks to a frequency doubler stage, the crystal frequency must be (F(receive)-10.7 MHz)/2.
From the mixer stage, the signal passes through two IF band filters to tube V4, which serves as a second mixer stage in which the signal is converted to the second IF of 1.65 MHz using a 9.05 MHz oscillator signal.
After four IF amplifier stages V5-V8, each coupled with a bandpass filter, the signal is fed to a limiter stage V8II; the IF for the direction finder is also picked up here. The AVC control voltage is picked up in diode V9I and demodulation takes place in a germanium diode D1. Tube V9II is used as a noise limiter, tube V10 is used for the squelch, the AF is muted below a certain signal level. Tube V11 is used as AF preamplifier; it is muted by the squelch circuit at low signals. The V12 AF power amplifier drives a 600 and a 5 ohm output and delivers 2 watts.

Tube configuration

Development

The large base VHF Doppler direction finder NP 4 was developed by Rohde & Schwarz in 1961 and was sold in various versions with crystal-controlled multi-channel systems, main and secondary bearing displays, etc.

A similar UHF direction finding system was sold under designation NP 5.

Use

Peilanlage P-722 The large base VHF direction finding system NP 4 from Rohde & Schwarz, developed around 1959, was bought in a number of seven units in 1962 for the Swiss Air Force. The system was used for air traffic control and surveillance at the Emmen, Dübendorf and Payerne military airfields and at three mountain sites.

The P-722 / NP 4 systems were in operation until 2011.

Technical documentation

Further information

en/p-722.txt · Zuletzt geändert: 2024/01/06 18:02 von mb