Learn SDR 02: Signal Generator into RTL-SDR

Learn SDR with Professor Jason Gallicchio at Harvey Mudd College
Lesson 2: Signal Generator as sine-wave transmitter and RTL-SDR receiver:

Transmit a sine wave from a signal generator simultaneously into a real oscilloscope and a BNC with hooks. The oscilloscopes only go to 100MHz, the RTL-SDR can tune down to 24MHz. Bandwidth of RTL-SDR is up to 2.4 MHz stable. Find a frequency to tune to that doesn't have much interference and can be seen on the 'scope -- probably below the FM band. Actually, 100 MHz looks nice, works, and is a round number.

Sample rate: 2.4MHz, 2MHz, or 1MHz might be good.

You get a complex exponential out of the RTL SDR. Why not a real sinusoidal signal? What does this complex number mean? Understanding this is half the SDR battle.

Tune the generator up and down. Tune the SDR up and down. See the signal go up and down in time and frequency and maybe constellation plots.

See it go below zero frequency and explain what's going on. "Negative frequencies!?" Observe that the real and imaginary parts either lead or lag each other depending on sign of frequency.

See that it's basically a constant (or at least very slow moving) when you're tuned spot on, but the phase is arbitrary.

You need to deal with these small oscillator mismatches when you use different hardware to transmit and receive -- oscillators drift in time and frequency and when you move around.

HW Check time signal at 25.000 MHz WWV North of Denver Colorado. Hm. Need to use 1MHz sample_rate because otherwise the bottom of the band is below the RTL-SDR limit.

https://gallicchio.github.io/learnSDR...

All GNURadio flowgraphs are at:
https://github.com/gallicchio/learnSDR

--- Learn SDR with Professor Jason Gallicchio