Software Defined Radio

Many devices we us today communicate wirelessly using electromagnetic waves. After some research, I purchased an RTL-SDR to take a look at some of these communications. 

After seeing some videos on YouTube of replay attacks as well as using Raspberry Pi’s to record, decode, and transmit signals to smart home devices, I knew I needed to try it for myself. 

Once I received the RTL-SDR, I installed SDR Sharp on my windows laptop and began scanning different frequencies to see what I found… What I found was an invisible world of devices and people communicating with one another over short and vast distances. I picked up the usual FM radio stations as well as some Ham Radio operators in and around New Mexico. 

After this, I was hooked, and I started looking into a way of scanning radio frequencies on the go without carrying around my laptop. I soon found a driver for the RTL-SDR on the play store as well as a version of SDR++ for android on GitHub. After installing, I was up and running on my old android phone with the SDR connected and scanning. I was able to pick up some interesting communications and weird signals (Digital or encrypted signals)

 After searching for different signal types I came across some articles about trunked systems that many police, security, construction crews, etc. utilize to communicate. This type of radio communication makes it difficult for listeners to follow a single conversation as the control channel dictates which frequency the conversation will occur on. I was able to utilize DSDPlus software along with information from www.radioreference.com (has control channels listed) to follow along these trunked communications. 

After this, I began using a Raspberry Pi Zero 2 W with RPiTX installed to record and transmit signals. I learned about antennas and how they are specifically designed to resonate with certain frequencies depending on length, orientation, and configuration. This part is remarkably interesting, and I learned a lot about radio waves, how they propagate through space, how we utilize them to carry information. I still have much to learn and am interested in getting my Technician License to transmit on specific channels at certain power levels. 

Other than the tinkering and learning with all of this that I find fun, there are many ways bad actors utilize these technologies to gain access to vehicles, buildings, and homes. Hijacking “smart” devices for nefarious uses. The defense against these attacks is just as interesting, and so much can be learned from observing both sides.