SDR-STK Parallel Functions
Here's a list of a few pieces of existing SDR software that work well together for parallel use cases with the SDR-STK.
Before we get into how these pieces of software work together, let's cover what they actually are and do.
You've most likely heard us talk about the rtl_power utility before, and for good reason. In our opinion, it's one of the most useful and versatile tools for RTL based SDR's. While it has a few issues (as of 12-13-22) such as the .csv output format and a lack of easy rendering tools, the concept behind it and the use you can get out of it is still incredible.
How rtl_power works is by measuring power across a band of frequencies rather than plotting an FFT like traditional "spectrum analyzer" type software does. This band can be anywhere from a few hundred Hz to the full 2.4MHz maximum bandwidth of the RTL-SDR. The software then proceeds to sweep the tuner across the provided frequency range, and outputs all of the dBm and frequency values in the format described at the bottom of the rtl_power docs page.
With this kind of power analysis, you can create some extremely useful wideband scans, such as this one by thotlin:
Another tool from the rtl-sdr set of utilities, rtl_tcp is exactly what it sounds like: a server for the RTL that streams IQ data over a TCP connection. Okay, it might not have been that obvious from the name, but what rtl_tcp basically does is allow you to start a server for an RTL that any software (that supports an rtl_tcp stream) can connect to. This allows you to share your RTL-SDR data over any IP network that's fast enough.
With the SDR-STK, combining rtl_power and rtl_tcp can allow you to take the input of a wideband scan coming from one of the tuners, and use that to change the center frequency of the second one.
- ADS-B DATA
ADS-B stands for "Automatic Dependent Surveillance–Broadcast," and is a "surveillance technology and form of Electronic Conspicuity in which an aircraft determines its position via satellite navigation or other sensors and periodically broadcasts it, enabling it to be tracked." Basically, ADS-B packets are just telemetry information from aircraft sent out over radio.
While gathering information about aircraft might at first seem like some weird plane nerd stuff, understanding what's in the airspace around you is a critical part of situational awareness. We've already seen several instances over the past few years where certain aircraft were seen suspiciously circling an area before some sort of "event."
There's a variety of both paid and free SDR ADS-B software for any platform you're using. While there are some online-based ADS-B receivers, if you're on our page reading this, you probably already understand why leaving mission critical information to the hands of infrastructure you don't control isn't the best idea.
Public Safety (PS) Trunked Radio Systems can be a wealth of useful, on-the-spot information given the ones in your area are unencrypted. Basically all trunked systems operate in the 7/800MHz band, and therefore can't be picked up with V/UHF radios. All trunked systems are digital, with the majority being P25.
While you can get a surplus 7/800MHz P25 radio and program it for conventional or NAS scanning, this is a lot more difficult to do than setting up an SDR-STK or RTL dongle and some software. You also don't run the risk of accidentally transmitting, or worse, your radio trying to associate to the system.
DOUBLE THE TUNERS, DOUBLE THE POWER
The easiest way to start reaping the benefits of a dual-tuner system like the SDR-STK is to simply run two instances of your favorite SDR software. Whether that be basic monitoring and demodulation, or two separate ADS-B receiver instances to cover both 1090MHz and 978MHz, this can be a great way to increase the amount of information you can ingest while doing SIGINT. For instance, running two rtl_power scans allows you to not only cover more bandwidth in less time, but also to also scan two completely separate chunks of the frequency spectrum at once. This can be a great way of spotting cross band repeaters or transmitters, even ones that are using an RF data input.
You can also run two separate pieces of software to get the simultaneous functionality of both. One of our favorite ways to do this on Android is to use split-screen to run both RF Analyzer and an ADS-B receiver. This allows us to keep track of RF activity on one tuner, while monitoring air traffic with the other. But the real fun begins when you start combining the functionality of several of these tools to solve unique problems.
SDR-Trunk is actually one of the few pieces of already existing software that utilizes the advantages of having two independent tuners. By tuning one the the trunked system control channel, the second tuner is available to switch to any frequency that pops up. This becomes especially useful when attempting to monitor larger or multiple PS systems that cover more than 2.4MHz of bandwidth.
Having the input of one tuner control the frequency of the other is obviously pretty useful, and this is what we did with our stk_sweep script. By taking power and frequency output from rtl_power and using a TCP proxy to be able to input frequency information to tune the second RTL, we got the ability to sweep across massive chunks of the RF spectrum in less than a few seconds and instantly view any RF activity. This script, along with other utilities, can be found (soon) on our GitHub.
There's a ton more that can be done with the SDR-STK (such as directional wideband scans, geolocated heatmaps, and potentially standalone TDOA node functionality), and the rugged form factor allows it to be easily packed into a bag, used in the field, and set up pretty much anywhere. Just remember that even the coolest radio gear in the world won't make you a good communicator. Learn the basics, test your SOP's, and push the limits as much as you can.