The Digital HF/VHF/UHF Monitoring Direction Finders R&S®DDF0xE cover the entire frequency range from 0.3 MHz to 3000 MHz or subranges thereof. The direction finders use digital signal processing both in filtering (FFT and filters with linear phase response) and in bearing calculation.
Each direction finder consists of four functional units:
- DF antenna system
- DF converter with integrated receiver modules
- Digital signal processing unit
- Control PC and software
The HF DF Converter R&S®EH110 is designed for the frequency range 0.3 MHz to 30 MHz; the VHF/UHF DF Converter R&S®ET550 covers the range 20 MHz to 3000 MHz. The Digital Processing Unit R&S®EBD061 has two IF inputs so that both DF converters (R&S®EH110 and R&S®ET550) can be connected to the R&S®EBD061 (see block diagram on page 3) at the same time. The software of the digital signal processing unit contains as standard the algorithms for DF evaluation according to the Watson-Watt method and the correlative interferometer.
Digital DF methods
The acronym DDF in the type designation R&S®DDF0xE stands for digital direction finder, indicating that bearings are determined digitally, i.e. the complex antenna voltages are measured by a high-quality three-path DF receiver that acts like a vector voltmeter and are subsequently digitized. The bearings are evaluated using mathematical algorithms. Both the classic Watson-Watt direction finding method and the modern correlative interferometer method can be used.
The Watson-Watt method is preferably used in the HF range in cases where only limited space is available for setting up a DF antenna (e.g. on ships). Moreover, it enables maximum scanning speed.