What is the legal status of spectrum analyzers in United Kingdom? Is it considered 'interception', despite only analyzing the magnitude of a frequency?

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    This is impossible to answer adequately without a better description of what a spectrum analyzer does and how it does it. Law.SE does not presume a readership with advanced technical knowledge. I think that I know what you are getting at, but it would be better if you could clarify this yourself. If there is a source that makes you think that the existence an "interception" is a critical issue it would also be helpful to cite to that source.
    – ohwilleke
    Commented Mar 27, 2019 at 21:48
  • In it's simplest form, a spectrum analyzer receives radio, tv, cell phone, and similar signals from an antenna or other source. It makes a graph; the x axis is the frequency and the y axis is the strength of the signal. So you can see that the signal exists, but you can't perceive what information the signal is carrying. (I don't know what the latest and greatest ones can do; maybe they can let you listen to the sound or see the video for certain signals.) Commented Mar 27, 2019 at 23:48

1 Answer 1


Presumably this refers to the Regulation of Investigatory Powers Act 2000, and the government's advice regarding interception of communications, where

Section 1(1) of RIPA makes it a criminal offence for a person intentionally, and without lawful authority, to intercept in the United Kingdom (UK) any communication in the course of its transmission if that communication is sent via a public postal service or a public telecommunication system.

The act apparently does not define what constitutes "interception".

A spectrum analyzer performs a kind of mathematical analysis on a physical signal which (very roughly put) says "here, the higher frequencies are loud and the mid-range frequencies are soft". You could subject a phone conversation to this analysis and get some information about an individual saying "Let's kill him" (information about "what that utterance sounds like"). In theory you might be able to figure out that a person said "Let's kill him" using that output, but that's close to the realm of science fiction than doable practice. But it's not clear whether that matters for the law. That is, the law isn't stated in terms of methods of extracting usable and possibly damning evidence from some transmitted signal, it simply prohibits "interception".

A frequency analyzer might be mostly hardware or mostly software, and points in between. The machinery itself is legal, and can be used legally or illegally (mostly legally), just as a tape recorder can be used legally or illegally. It would be illegal to record a phone conversation (recording is a form of interception, one that preserves most of the information in the signal). It would, technically, be illegal to spectrum-analyze a phone conversation (another form of interception, one that doesn't preserve enough of the information to be of use for prosecution). There isn't anything in the act that says "but interception is legal if the product is not practically usable in a prosecution".

  • Thank you. Spectrum analyzers don't show any data on a frequency, it shows the magnitude of a frequency. But you never know what's considered 'interpretation' by the laws.
    – mike1024
    Commented Mar 28, 2019 at 8:35

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