0×00 前言
在第一篇文章：永不消逝的电波（一）：无线电入门篇 我们了解了一下无线电的发展史以及无线电的一些物理知识，在第二篇里我们将用HackRF录制家用门铃的无线信号，然后重放门铃信号。
门铃从某宝买的，如图：
0×01 环境搭建：
MAC下可以用gqrx和hackrf (需要有Xcode、Mac Port的支持)
sudo port install gnuradio sudo port install hackrf sudo port install rtl-sdr sudo port install gr-osmosdr sudo port install hackrf
sudo port install gqrx
也可以参考：在Mac上安装HackRF环境
0×02 步入正题：
安装完成以后，插入HackRF,终端执行 hackrf_info:
hackrf_info Found HackRF board. Board ID Number: 2 (HackRF One) Firmware Version: git-815d1f6 Part ID Number: 0xa000cb3c 0x00664f49 Serial Number: 0x00000000 0x00000000 0x583064c0 0x2640ad4b
#通过终端启动gqrx
gqrx
按下遥控器，我们可以看到信号的频率在314.100000Mhz(读作：314.1兆赫兹)左右
1Mhz=1000000hz; 1Khz=1000hz 314.1Mhz=314100000hz;
关掉gqrx启动hackrf
hackrf_transfer Usage:
Usage: -r <filename> # Receive data into file. 把接收到的信号、数据保存到文件中；（信号录制） -t <filename> # Transmit data from file. 从文件中提取、发送射频信号；（信号播放） -w # Receive data into file with WAV header and automatic name. # This is for SDR# compatibility and may not work with other software. [-f freq_hz] # Frequency in Hz [0MHz to 7250MHz]. [-i if_freq_hz] # Intermediate Frequency (IF) in Hz [2150MHz to 2750MHz]. [-o lo_freq_hz] # Front-end Local Oscillator (LO) frequency in Hz [84MHz to 5400MHz]. [-m image_reject] # Image rejection filter selection, 0=bypass, 1=low pass, 2=high pass. [-a amp_enable] # RX/TX RF amplifier 1=Enable, 0=Disable. [-p antenna_enable] # Antenna port power, 1=Enable, 0=Disable. [-l gain_db] # RX LNA (IF) gain, 0-40dB, 8dB steps [-g gain_db] # RX VGA (baseband) gain, 0-62dB, 2dB steps [-x gain_db] # TX VGA (IF) gain, 0-47dB, 1dB steps [-s sample_rate_hz] # Sample rate in Hz (8/10/12.5/16/20MHz, default 10MHz). [-n num_samples] # Number of samples to transfer (default is unlimited). [-c amplitude] # CW signal source mode, amplitude 0-127 (DC value to DAC). [-b baseband_filter_bw_hz] # Set baseband filter bandwidth in MHz. Possible values: 1.75/2.5/3.5/5/5.5/6/7/8/9/10/12/14/15/20/24/28MHz, default < sample_rate_hz.
hackrf_transfer -r /dev/stdout -f 314100000 -a 1 -g 16 -l 32 -s 8000000
没按遥控器
按下遥控器：
由于hackrf_transfer后面没带解码参数，so我们看到一堆乱码数据；
0×03 录制信号&信号分析
录制遥控的无线信号：
hackrf_transfer -r door.raw -f 314100000 -g 16 -l 32 -a 1 -s 8000000 -b 4000000
终端输出：
hackrf_transfer -r door.raw -f 314100000 -g 16 -l 32 -a 1 -s 8000000 -b 4000000 call hackrf_sample_rate_set(8000000 Hz/8.000 MHz) call hackrf_baseband_filter_bandwidth_set(3500000 Hz/3.500 MHz) call hackrf_set_freq(314100000 Hz/314.100 MHz) call hackrf_set_amp_enable(1) Stop with Ctrl-C 16.0 MiB / 1.005 sec = 15.9 MiB/second 16.0 MiB / 1.003 sec = 15.9 MiB/second 16.0 MiB / 1.004 sec = 15.9 MiB/second 16.3 MiB / 1.004 sec = 16.2 MiB/second 16.0 MiB / 1.002 sec = 16.0 MiB/second 16.0 MiB / 1.001 sec = 16.0 MiB/second 16.0 MiB / 1.004 sec = 15.9 MiB/second 16.0 MiB / 1.003 sec = 15.9 MiB/second 16.3 MiB / 1.003 sec = 16.2 MiB/second 16.0 MiB / 1.003 sec = 15.9 MiB/second 16.0 MiB / 1.005 sec = 15.9 MiB/second ^CCaught signal 2 8.1 MiB / 0.510 sec = 15.9 MiB/second User cancel, exiting... Total time: 11.54724 s hackrf_stop_rx() done hackrf_close() done hackrf_exit() done fclose(fd) done exit
信号波形分析：
这里用到的软件是Audacity，导入录制的音频信号（未压缩原始数据）
然后出现如下界面：
使用默认参数，直接导入：
中间的那部分就是按下遥控时录制到的无线信号，我们使用Audacity的放大镜放大来看：
继续放大我们可以看到：
继续放大：
再放大：
这时经验比较丰富的童鞋可以通过图形，把无线射频信号转换成二进制数据：01010101**** ，接着可以把二进制写到GRC（Gnu Radio Cpmpainon）,制作一个框图，使用GNC项目重放无线信号，大致方法如下：
启动Gnu Radio Cpmpainon ：Kali Linux—->无线攻击—>Software defined Radio—>GnuRadio-Companion
源：在右侧Misc一栏找到Vector Source
通过搜索添加Repeat（old）、Moving Average、osmocom Sink
四个组件：
按照流程连线：
GNC用得不多，暂时还不上手，这种方法以后再试 :）
0×04 信号重放
使用hackrf_transfer重放信号：
hackrf_transfer -t door.raw -f 314100000 -x 47 -a 1 -s 8000000 -b 4000000
终端输出：
hackrf_transfer -t door.raw -f 314100000 -g 16 -l 32 -a 1 -s 8000000 -b 4000000 call hackrf_sample_rate_set(8000000 Hz/8.000 MHz) call hackrf_baseband_filter_bandwidth_set(3500000 Hz/3.500 MHz) call hackrf_set_freq(314100000 Hz/314.100 MHz) call hackrf_set_amp_enable(1) Stop with Ctrl-C 16.0 MiB / 1.004 sec = 15.9 MiB/second 16.0 MiB / 1.004 sec = 15.9 MiB/second 16.0 MiB / 1.003 sec = 15.9 MiB/second 16.0 MiB / 1.001 sec = 16.0 MiB/second 16.0 MiB / 1.000 sec = 16.0 MiB/second 16.3 MiB / 1.001 sec = 16.2 MiB/second 16.0 MiB / 1.003 sec = 16.0 MiB/second 16.0 MiB / 1.001 sec = 16.0 MiB/second 16.0 MiB / 1.005 sec = 15.9 MiB/second 16.0 MiB / 1.003 sec = 15.9 MiB/second 16.3 MiB / 1.003 sec = 16.2 MiB/second 8.4 MiB / 1.004 sec = 8.4 MiB/second Exiting... hackrf_is_streaming() result: HACKRF_ERROR_STREAMING_EXIT_CALLED (-1004) Total time: 12.03184 s hackrf_stop_tx() done hackrf_close() done hackrf_exit() done fclose(fd) done exit
0×05 演示视频
熊孩子的正确使用姿势是这样的：
for i in {1..999}; do hackrf_transfer -t door.raw -f 314100000 -g 16 -l 32 -a 1 -s 8000000 -b 4000000; done
嗯，你没看错，重复播放九百九十九次 :）
0×06 参考：
Exploring Bluetooth & iBeacons – from software to radio signals and back.