Testing a Software Defined Radio Minimum Detectable Signal on HF

Some neat testing by David Rowe in Australia who has used HF radio and open source to connect people in rural communities. His current work involves low cost software defined radios and the analog to digital conversion resolution. He writes:

There’s a lot of discussion about ADC resolution and SDRs. I’m trying to develop a simple HF data system that uses RTL-SDRs in “Direct Sample” mode. This blog post describes how I measured the Minimum Detectable Signal (MDS) of my 100 bit/s 2FSK receiver, and a spreadsheet model of the receiver that explains my results.

Noise in a receiver comes from all sorts of places. There are two sources of concern for this project – HF band noise and ADC quantisation noise. On lower HF frequencies (7MHz and below) I’m guess-timating signals weaker than -100dBm will be swamped by HF band noise. So I’d like a receiver that has a MDS anywhere under that. The big question is, can we build such a receiver using a low cost SDR?

Check out David’s well reasoned blog post for more info and his conclusions.