Noise of the Waves

Following on from recent beach work, John, EI7GL, asked a very valid question about the potential difference in HF noise floor between home and beach.

I'd always judged this on experience, and considered there was little or no difference in the noise floor.  But that's no way to go about science, so I set off for a very brief session of noise assessment this evening.

A quick noise floor assessment at the beach, looking landward (East).

I used a Windows 10 laptop to run SDRUno software, coupled to a RSP1a receiver and a 14MHz, 1/4 wave elevated vertical with two elevated radials for both sites.

I wouldn't claim that the result is accurate in absolute terms, not least because there is always a fair bit of fluctuation in the output.  But I think it is, as a comparison between sites, perfectly valid.  I kept the settings exactly the same for both sites, over a bandwidth of 1800Hz.  The weather was electrically quiet, nearest lightning slight, over eastern Europe and central Spain, a fine sunny day with a gentle breeze.

The result?

Home noise floor, with LED TV on in the living room, various other domestic things, but none of a known noise-generating nature:  -110dBm (a 'rural' noise level, according to the ITU).

At the beach: -111dBm.

It seems my ears are pretty good at comparing the noise floors!  From the more considered online discussions, it seems the RSP1a itself, when using a terminated input, yields a noise floor of about -120dBm.

ITU Noise floor classifications.