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by ralferoo 5 days ago
By "obviously there", I meant take some old analogue receiver and twiddle the tuning knob. The vast majority of radio transmissions are many orders of magnitude louder than the noise floor. They are very obviously there.

Tune your SDR radio down to 1.023MHz, you'll see nothing there at all. The signal is about 20dB below the noise floor. The only way you can pick out anything at all is by correlating it against the PRNG with the correct offset in the sequence.

The GP post (to be fair, I should have replied to the post 2 higher up) was arguing that all signals are weaker than the noise floor and demodulating using a carrier was exactly the same thing. It is in one way, but also not in another - in that you need to keep trying different offsets in the PRNG sequence until you find a correlation. That's why I think "correlation" is a sensible term for Gold Codes, but "demodulation" is better for signals modulated by a sine wave carrier.

1 comments

What you're describing is correlating the received signal with complex sine wavelets of various frequencies.