Everyone has those moments throughout their day when it seems as if the day will never end, especially when work is slow. Today while passing some downtime I started googling interesting things to do with an RTL-SDR. Of course google is helpful, but I quickly search for something else: RTL-SDR Reddit.
Since anything and everything can be found on Reddit, I went to the RTL-SDR Subreddit. I wanted something quick and easy to do while utilizing the cheap bunny ear antenna that came with the dongle, so I scrolled past many posts that talking about 1090 MHz/ADS-B flight information. Further down, I came across this humble post with only 5 upvotes. The user was explaining that he wanted to pick up packets from his utility meter. Knowing that I have a smart meter, I tried to locate my meter’s data in the 900 MHz ISM band as the referenced Stanford article mentioned. I looked, but couldn’t find anything, so I just grew bored and started moving around in the band. I stumbled on 929.611.500 MHz and being fairly new to all things radio excluding commercial cellular, I thought it kind of looked like AM, so I switch my modulation and hear awful screeching. Googling 929 MHz showed me that it was a POCSAG paging frequency. I knew of POCSAG but I didn’t know it was still used since we all have easy access to cell phones. So there, I had my super easy project to pass the time.
I downloaded a program called PDW Paging Decoder Software and thumbed through the setup manual a bit. I opened up SDR#, PDW, and configured my computer’s audio to a virtual audio cable out, and a virtual audio cable in. As soon as you open up PDW, select you interface and make sure the right audio device is selected (virtual cable). Set up SDR# to the center frequency of the POCSAG signal, in my case 929.611.500 MHz, and change the modulation to Narrow FM with a bandwidth of 12.5 KHz. At this point you should see PDW working, but a bunch of broken messages. As long as you can see some messages in PDW, your set up should be functioning properly. You’ll need to fine tune SDR# by changing the audio and gain to allow PDW work most efficiently. There you have it, you should see ton’s of messages populate and most of the messages that aren’t obfuscated will be readable in plain text.
I guess I was wrong, people use POCSAG all the time, I only received messages from hospitals and doctors, which makes complete sense. The last time I was in the hospital I remember seeing doctors and nurses with the “beepers” on their waistband. It’s the little things like stumbling across POCSAG that makes me happy.
Here is a video of PDW and SDR# working together (please excuse the low quality, OBS doesn’t seem to like laptops):