Tags: radio 


# Turning In

##### Score : 100

### Challenge

We recorded another flag... but Steve forgot to tune the radio to the proper frequency. All I hear is some music station. Come on, Steve.

rf2.iq: https://drive.google.com/file/d/1R7As6djHhA-hs2GjQByhHU2ON_jPnOR5/view?usp=sharing

This IQ file was again saved in standard GNURadio format (complex, 32bit float I, 32bit float Q)

Author: nb


### Description

This file is IQ format, it's basically capture some radio frequency in file. Like pcap files on Wireshark.

I used the SDR (Software Define Radio) Software, named "SDR#" but it's can't not import the IQ file directly so, It must be changed into wave file.

And I tried to covert this file into wav, to using iqToSharp to covert iq file to wav file.


Then import into SDR# with file player plugin.


There is few spot to get signal from noise.

But the every spot is not a flag. As you can see there is few peak point in here, and this peak point contain flag. You can see the 2 types of peak point here. Wide bandwidth is Just only Radio Station, but you can see the narrow bandwidth is the flag.

![https://raw.githubusercontent.com/Dobob1022/CTF/main/2021/Dawg%20CTF%202021/Tuning%20In/Picture_Sound/radiostation.PNG](https://raw.githubusercontent.com/Dobob1022/CTF/main/2021/Dawg%20CTF%202021/Tuning%20In/Picture_Sound/radiostation.PNG)**Radio Station Frequency** (wider than flag frequency)


**Flag Station Frequency** (narrow then radio station frequency)

This challenge have hint about modulation, "FM" but SDR have 2 types of FM demodulation, NFM and WFM.

NFM is Narrow band FM, WFM is Wide band FM. but WFM have wide bandwidth, So WFM is not suitable on this Challenge. So I use NFM to find the flag sound with narrow bandwidth.

Finally I find the flag station frequency, it's 104.500Mhz(The Frequency will different Depend on your sampling rate)

But! The sound quality so suck, I just hear the only "The Flag is". and I can't hear the flag.
You Can here flag on this file.


Original writeup (https://github.com/Dobob1022/CTF/tree/main/2021/Dawg%20CTF%202021/Tuning%20In).