Editing Direction finding (section)

=== A typical DF system with six antennas ===
[[File:Schematic_of_6-port_DF.png|thumb|right|upright=1.75|Six-port DF system]]

A schematic of a possible DF system,<ref name = Lipsky />{{rp|101}} employing six antennas,<ref>Blake B. (ed.), " Cutlass ESM Equipment", Jane's Radar and Electronic Warfare Systems, 3rd Ed., Jane's Information Group, 1991, p. 406</ref><ref>Streetly M., "SPS-N 5000 ESM System",  Jane's Radar and Electronic Warfare Systems, 10th Ed., Jane's Information Group, 1998, p. 396</ref> is shown in the figure.

The signals received by the antennas are first amplified by a low-noise preamplifier before detection by detector-log-video-amplifiers (DLVAs).<ref name = MITEQ>MITEQ, "IF Signal Processing Components and Subsystems", Application Notes" pp. 33-51, (2010), Find at: https://nardamiteq.com/docs/MITEQ_IFsignal_c17.pdf</ref><ref>Pasternack, " Broadband Log Video Amplifiers". Find at: www.pasternack.com/pages/Featured_Products/broadband-log-video-amplifiers</ref><ref>American Microwave Corporation, DLVA Model: LVD-218-50. Find at: www.americanmic.com/catalog/detector-log-video-amplifiers-dlva/</ref>  The signal levels from the DLVAs are compared to determine the angle of arrival. By considering the signal levels on a logarithmic scale, as provided by the DLVAs, a large dynamic range is achieved <ref name = MITEQ />{{rp|33}} and, in addition, the direction finding calculations are simplified when the main lobes of antenna patterns have a Gaussian characteristic, as shown earlier.

A necessary part of the DF analysis is to identify the channel which contains the largest signal and this is achieved by means of a fast comparator circuit.<ref name = East /> In addition to the DF process, other properties of the signal may be investigated, such as pulse duration, frequency, pulse repetition frequency (PRF) and modulation characteristics.<ref name = NAWC /> The comparator operation usually includes hysteresis, to avoid jitter in the selection process when the bearing of the incoming signal is such that two adjacent channels contain signals of similar amplitude.

Often, the wideband amplifiers are protected from local high power sources (as on a ship) by input limiters and/or filters.  Similarly the amplifiers might contain notch filters to remove known, but unwanted, signals which could impairs the system's ability to process weaker signals.  Some of these issues are covered in [[RF chain]].