Steve notes the ITU-R Recommendations on Radio Noise

SX-99-Dial

Commenting on our post about the FCC Noise Floor Inquiry, SWLing Post contributor, Steve Yothment writes:

One of the definitive documents on Radio Noise is the ITU-R Recommendation on Radio Noise, version P.373-12. This (latest) version is dated 07/2015, so it’s only a year old. You can download it [as a PDF] here. It has a lot of info on natural and man-made radio noise.

My favorite graph from the document is shown below:

Graph

It shows the level of radio noise vs. frequency for good and poor conditions. It can be rather surprising how noise, even under the best conditions, can be quite excessive on shortwave frequencies. For example, the best case noise level for 10 MHz is about 30dB above the Johnson Noise level. (That’s the noise level from just a resistor at room temperature.) That’s why the noise level in your shortwave receiver’s speaker gets so much higher when you attach the antenna!

That is fascinating, Steve! It’s no wonder we struggle with noise issues–even in the best of times, it appears.

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1 thought on “Steve notes the ITU-R Recommendations on Radio Noise

  1. DL4NO

    This diagram is decades old. It explains several important things:

    * The lower the frequency, the more transmitter power is needed. Add to it that it gets difficult even for commercial transmitters to build “full-size” antennas below 1 MHz (> 300 m wavelength) or so. Shortening an antenna reduces its efficiency.

    * Up to perhaps 30 MHz the efficiency of a receiving antenna is unimportant. A good amplifier will add hardly any noise.

    * For a shortwave receiver sensitivity is only important if you want to use a very tiny antenna like the telescopic rod of a handheld unit. But do not directly connect such a receiver to a “good” antenna, it will overload.

    * The best receiving antennas have some form of directivity that helps to suppress noise and signals from unwanted directions.

    Reply

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