What is that signal

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What is that signal

Post by Antti »

Nice looking frequency hopping signal. But what is it? Bluetooth?

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Re: What is that signal

Post by piranha32 »

Say 'Hi' to your microwave :)
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Joined: Thu Jun 06, 2013 8:15 pm

Re: What is that signal

Post by jynik »

Update: Gah! By the time I got done typing this up, wandering off to get coffee, forgetting what I was doing, and then finally submitting the post, you beat me to it piranha32! :)

You didn't happen to have a microwave oven running when you captured this, did you? While I'm quite new to all things RF myself (i.e., there's a high liklihood that I don't know what I'm talking about), I recall someone sharing a similar looking waterfall and noting it was from their microwave oven.

FWIW, here's a video looking at bluetooth FHS.

If you want to investigate further, you could capture samples a few different ways. One way would be to use the bladeRF-cli's 'rx' command to save samples to a binary format (specifically the native DAC format, signed-complex 16-bit values, with 11 decimal places, SC16Q11). After viewing the signal as you were doing, you could exit the viewer and open the bladeRF-cli. The device should remain at the same samplerate, tuned to your desired frequency. You could verify this via 'print frequency' and 'print samplerate' commands.

Code: Select all

bladeRF> rx config file=/dev/shm/mystery1.sc16q11 format=bin n=1M
bladeRF> rx start

bladeRF> rx

... The capture is complete when you see the state read "Idle" rather than "Running" ...
Depending how long of a capture you want, play with the n parameter. Remember that samples are 32-bits (16 for I, 16 for Q). So at 20Msps, capturing 1M (1024 * 1024 * 1024 in the CLI currently) samples, you're looking at little less than a 20ms long capture, totaling 4MB.

/dev/shm is recommended when possible, to ensure file I/O is as quick as possible. (Avoid hard disks.)

From there, you could open this file in something like baudline.
  • Run baudline
  • Right click, input, open file
  • Select /dev/shm/mystery1.sc16q11, with "File format" set to "raw"
  • In the next window, use the following settings
    • Decompression = off
    • Initial byte offset = 0
    • Sample Rate = Custom, 20000000 (I think I saw you running at 20Msps)
    • Channels = 2, quadrature
    • Decode format = 16-bit linear, little endian
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