Radio direction finding

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New for February 2023. Radio direction finding (RDF) is almost as old as radio itself.  As is most often the case, a lot of effort was put into it for wartime efforts, and to this day it is still an important branch of electronic warfare.

In the video we have selected, many of the classic automatic direction-finding schemes are described, with pros and cons. There are four parameters that can be used to get a bearing on a signal. These include:

  • Amplitude - Watson-Watt's 1930's era set-up that is fast enough to locate lightning strikes. Watson-Watt is a founding member of the Microwaves Hall of Fame!
  • Frequency - Doppler shift can artificially be created with a switched antenna set-up.
  • Phase - correlative interferometry. The video does mention this, but a monopulse antenna is a form of interferometer that is used to track targets.
  • Time of arrival - this approach requires a synchronous clock between multiple sites, and is "widely deployed" in radio astronomy.  Luckily, we have GPS to time-stamp everything!

The subject video was produced by Rohde and Schwarz and is of excellent quality. Below we have bookmarked the four methods if you want to fast-forward to your particular interest.

Doppler systems start at 8:40

Watson-Watt starts at 15:40

Correlative interferometry starts at 21:28

Time of arrival starts at 25:48

An Introduction to Direction Finding presented by Paul Denisowski

Note that there are other ways of finding the source of radio emissions.  For example, law enforcement can "ping" your cell phone and read its GPS coordinates.

Author : Unknown Editor