Generating FSK Modulated signals in GnuRadio

Question

I am trying to recreate the signal from the RC car toy and control it with HackRf and GNU-Radio.

I have identified following:

• Controller operates on 2.463 GHz
• The bandwidth is 1MHz
  • Logical "1" 2.4635 GHz
  • Logical "0" 2.4625 GHz
  • Baud rate 1e6 samples
• I have demodulated the signals with Quadrature Demod block and I have extracted the sequence of 1s and 0s
• I created the binary file which stores the 0s and 1s pattern that I would like to transmit.

Now I want to recreate this signal based on the upper parametrs. Through some research I came up with the following setup for transmission:

But I have several questions that I am not sure how to resolve:

1. Based on this paper I have found out that there is a relation between modulation index, sample rate and difference between frequencies (screenshot from there):

Based on that I have set sample rate to 2M, BT to 0.5, but I am not sure if thats right.

2. Also I dont quite understand how to adjust other parameters and what they mean.

I would really appreciate if somebody can give intuitive explanation on how these things should be adjusted.

EDIT:

I also implemented new schematics based on the Tutorial from GNURadio about FSK:

Sniffing with other HackRf I couldn't find any signal transmitted, can you tell me what is wrong with this setup or what would be the best approach to recreate the required signal?

Answer 1

For starters, what is the objective of your project? If it is just to mimic what your RC controller is doing, you could store the received bits into packed bytes and write a file. But, I would start with a thorough analysis of the signal from your RC toy: a) what are the audio frequencies, or at least what is the difference between the high and low tones? are there more than two tones? how do you know it's FSK? b) what is the bit time, i.e. the shortest period you can find between transitions? that determines the baud rate. With no documentation, you have a lot of experimenting to do on the receive side before you can attempt to transmit anything meaningful. Maybe you can find something in the RC literature about it.