The R&S DDF 0xA family with its extremely high search speed constitutes the current generation of search direction finders. It comprises pure HF (R&S DDF 01A) or VHF/UHF direction finders (R&S DDF 05A) as well as combined HF/UHF/VHF direction finders (R&S DDF 06A).
The FFT realtime bandwidth is 1 MHz (10 MHz optional) in the HF range and 10 MHz in the VHF/UHF range. The frequency range has been extended down to 300 kHz and up to 3000 MHz. All antennasof the R&S ADDx series plus the Antenna Interface R&S GX060 can be used.
Digital DF methods
The type designation R&S DDF 0xA is derived from the term "digital direction finder" to indicate that bearings are determined digitally, i.e. the complex antenna voltages are measured by the high-quality triple DF receiver that acts like a vector voltmeter and are subsequently digitized.
The bearings for any individual signal are evaluated in parallel and independently on the basis of mathematical algorithms. Evaluation can be performed by means of classic direction finding methods such as Watson-Watt or the modern correlative interferometer method.
The correlative interferometer has the following advantages over classic methods:
- Reduction of DF errors caused by reflections and depolarization
- Determination of a reliable DF quality criterion for assessing and filtering bearings
- Possibility of using wide-aperture DF antennas with a minimum number of antenna elements (preferably circular array)
The essential features of the Watson-Watt method are:
- Maximum search/direction finding speed with three-path evaluation (only one measurement step required)
- Use of antennas with small dimensions in the HF range
- Easy adaptation of available Adcock antennas (especially in the HF range)