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:
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.