I’ve recently been building a link budget for my ground station. I notice that no matter what given the noise bandwidth of the SDR I’m using, the signal to noise ratio is negative. That would imply there is more signal than noise and as such nothing useful is received. How is it that people are still capable of making observations from low power transissions from birds such as Havelsat using an omnidirectional antenna which gives a negative SNR? Does the SDR do something to the signal to retrieve information from the noise? How does that work? Any ideas?
I was under the impression that the bandwidth used for the noise calculation when using the SNR method was the bandwidth of the receiver itself. Is that not so?
Interesting. So this reduces the noise bandwidth of the receiver? And thus the overall noise production of the SDR? Thank you for taking the time to educate me, by the way. It is really very much appreciated.
Yes, a filter has the same function from a signal theory point of view regardless of whether it is analog or digital. We like digital filters running on a computer because they can have better performance, but we need the analog filters for high frequency front end filtering – at least until we can afford gigahertz sampling and processing