 Okay, this video is part of a series. Be sure to check out the full playlist in the description of this video. It should also be linked at the end of this video, if I don't forget to do that. Now, we're working with sending data over the airwaves using audio frequencies, and last time we used a little FM transmitter and a USB RTL-STL... RTL? Yeah, RTL-STL, real tech dongle there to receive it. Yeah, this is just for fun. This is not a practical use for this, but we're seeing if we can. Last time we did it with a GUI interface, but we want to script this out to be able to do it all on the shelf with just one or two commands. So let's go ahead and do that. My mp3 player has died. The battery is dead. So I'm going to go ahead and play the mp3 on my phone, and my phone still has a headphone jack, so I'll go ahead and plug in this FM transmitter, and we should be transmitting over at, let me get this focus, 89.9 FM. Now, in this shell, I'm going to start up Minimodem. Minimodem to receive at 110, and I'll just leave that running. So as soon as we start catching that audio, it should start displaying the tree of files down here, because that's the audio that we're sending, which is the information for just a list of files in a directory on my computer. Now, as I mentioned in the previous video, I knew there were commands that I can run to capture FM radio, and what I was going to be using was an RTL command. If I hit RTL underscore and hit Tab a few times, you can see there's a few applications I have installed, one of them being RTL underscore FM. I am running Debian on this system, and if I use aptitude or apt-get to search for RTL, which you got a list of applications here, one of which is this RTL-SDR. Right here, you can see software defined radio receiving and RTL, it says tools. So all those RTL applications should be part of this pack. Luckily, there is some very good documentation for this. So if I use men RTL underscore FM, we get this man file here that we can go through, and it lists out all the commands, all the options, and at the end, it even gives you some examples on how to use it. Now, if I was to quit out of this, and I was just to run our command RTL underscore FM news dash F, and as I said, we're doing 89.9 megahertz. If I hit that, you can see that we start getting just the raw data that it's retrieving from that FM signal, which is not what we need. Well, it is what we need, but we need to convert it. So if we run that same command, we can pipe it into the play command, which the play command is part of the socks package. So make sure you have socks installed aptitude search, if you have aptitude installed or use apt or apt to get or wherever package manager you prefer. And we do socks. Here you can see that I have socks installed. Now I'm not going to a whole lot of detail on this command that we're about to run, but I'll go over some basic parts of it, and I'll be sure to put a link to this command or two commands in the description of the video. So be sure to check that out. Let's have a quick look at this. So our command starts off with RTL underscore FM dash F and the frequency we're going at. Now I'm transmitting at 89.9, but both this receiver and the transmitter are probably not very accurate. I started off at 89.9, I tried going up a little bit, I tried going down a little bit, and I find that I'm getting the best signal at 89.8 megahertz in a particular case. So play with it, tweak the number up down a little bit, make sure you get a good calling. Next is just sample rates and other things on retrieving it, but then over here we're going to be piping it into the play command. So we're taking the output, the raw data, and we're going to pipe it into the play command, which is going to play it through our speakers. Now, and then we have some information out there, and then at the very end there's a dash, which just means play the audio. We're not saving it to a file, we're playing it. And many of them is going to be listening to what our computer is playing. It took me a little while of tweaking this, and on the RTL underscore FM, I finally found that 32K is not the best. That's the default. In fact, there's a command that we can do here telling it to use WFM modulation, I believe is what it was called, which basically puts in this command. I found that for me, 33 was a good number. So you might want to tweak that number a little bit for you. It's a sample rate there. Now we already have Mini Modem running, so when I hit enter on our program to start capturing the signal being sent, we should start receiving the text. Now, I will say also that I have found every time I do this, the first few seconds, there's a clicking noise which prevents the transmission from coming through, but eventually it comes through clearly. So let me go ahead and hit enter, and there we go. Our text starts coming through. So I'm not sure why the first few seconds, it doesn't come through clear, but eventually it comes through clear, and we start getting our list of directories that we're transferring over. That's it. So that is our example. Again, this is not practical doing it with this particular setup, but it is possible to information from one computer to another using an FM transmitter and a USB dongle. So $20 worth of transmitting and receiving hardware, because the transmitter was about $10, and I bought my SDL dongle. What did I say? Yes, RTL SDL dongle. Why am I saying that wrong? You know what I mean. I bought for about $20, but that was a couple of years ago. I'm pretty sure you can get them for $10 to $15 now. It's a fun little thing to do, and we're transmitting text, but something like Base64, technically you could transmit binary data this way, images, and other stuff that just would take a long time, because you got to go so slow to get a clear signal, as I've talked about in the previous videos of this series. So I think that's it. Thank you for watching, and I hope that you have a great day.