Improvements in or relating to high frequency direction finding systems

摘要

853,662. Aerials; radio direction-finders. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Feb. 15, 1957 [Feb. 15, 1956], No. 4769/56. Class 40(7). A radio direction-finder comprises fifteen or more static aerials arranged in a circle of 5 to 10 wavelengths diameter and phase modulation of the received signals in a frequency changer energized from a phase-modulated oscillator such that all received signals are brought to a common phase at one point on a circular time base to indicate bearing. If there are n aerials in the ring and the amplitude and phase of the k th. aerial output are E k , # k the apparatus carries out the summation where # k is a phase delay made to vary as R cos (# o t - 2k #/n), R being an adjustable parameter and # o the angular frequency of phase modulation of the delay. It is demonstrated that # o t corresponds to azimuth, and the maximum value of voltage V 2 as displayed on a circular time base of angular frequency # o gives the bearing of the received signal. A signal of frequency # o /2# (25 c/s.) from oscillator AO and a quadrature signal from phase shifter PSI are multiplied by factor R in attenuator AT whose outputs are fed to the modulating units of each aerial. The 25 c/s. cosine and sine components are multiplied by cos (2 k#/n) and sin (2k#/n respectively in units Nc, Ns and their outputs are added in unit AD1 the output of which (R cos{# o t-2k #/n}) is fed to balanced modulator BAM the other input to which is a signal f 1 from oscillator O. A phase quadrature signal of frequency f 1 is added to the balanced modulator output in unit AD2 whose output is frequency multiplied to give a phase modulated signal input to frequency changer FC2. The k th. aerial output after frequency changing in unit FC1 fed also from local oscillator RO is taken to the other input to frequency changer FC2 the output of which is added to similar outputs derived from the other aerials of the ring in unit AD3. After linear detection an output voltage, which is V 2 , is taken to time base circuits CTB1, CTB2 to afford the bearing display on cathoderay tube (CRT) CRTC. A linear time base occupying a fraction of the circle of azimuth is provided for CRTF for more accurate measurement. Alternatively the CRT's may be fed from a phase sensitive detector PSD whose inputs are from amplifier 1A1 and adjustable phase shifter PS3; the phase shifter input comprises the signal from a centre aerial CA after successive frequency changing by inputs from oscillator RO and the frequency multiplied output of phase shifter PS2. To cover a wide frequency range three concentric rings of aerials are provided. Each aerial is a short vertical unipole. In order to align the system, a test signal is transmitted from the central aerial CA and each of the channels from the aerials in the ring are adjusted on this signal to give voltages of the same phase and amplitude at AD3.