[Silly] App idea: NFM radio

Sub-GHz
#1

Note: after some calculation, I consider this impossible. Dumping for future explorers and in case I’m wrong.

While CC1101 doesn’t support analog radio, it might be possible to receive NFM on UHF - some portable radios live there. To do so, make a few AM receptions on adjacent frequencies, discarding data, but retaining RSSI. In fact, I got this idea playing with my walkie-talkie and figuring out that Spectrum Analyzer spectrogram looks almost normal.
After that, we have a FM spectrum snapshot and some DSP will get us an audio sample.

So, how bad will it be? Critical part is acquiring many samples fast enough. Retune time when hopping between predefined frequencies is 75 us (reference: section 28.2.2 of datasheet). Assuming we read batches of 100 subsamples, getting slightly less than 7-bit audio (with FM, more frequency resolution on input = more amplitude resolution on output; 7-bit speech is OK, and we can’t get much more due to our speaker), it takes 7.5 ms for one sound sample. Reciprocal: audio rate will be 133 Hz, leaving voice tones of less than 60 Hz per Shannon-Nyquist. Normal voice is around 500 Hz.

Conclusion: Flipper’s hardware probably won’t cut it.

If you find any mistakes, please tell me.

1 Like
#2

This is what Flipper should get credit for. Inspiring all kinds of creative ideas!

1 Like
#3

True

#4

Have you seen this?

Flipper Zero TEA5767 External Radio Module

#5

Some of these modules are a little silly to me. This module for instance turns the Flipper into an expensive screen and some buttons. It’s still great if it gets someone interested in electronics but I’m not sure it teaches the user anything.

#6

The Flipper Zero cc1101 radio doesn’t do FM or AM broadcast radio, you would need to wire a radio receiver of some sort to do so.
This is the only way you will be able to get FM radio on a Flipper Zero and this module does that cheaply and easily.
HackRF with the portapack is capable of listening to FM or AM radio but it is a totally different type of device.
You could just get a $5 FM radio and listen to it while using your Flipper too.

#7

The proposal wasn’t to receive broadcast FM or Broadcast AM. NFM just means Narrow FM. It’s used for two way communication. Those TV dongles that sparked the revolution of SDR have been pushed way beyond what we could have ever expected they can do so I don’t want to rule out a creative idea like this.