(Continued from Part 4. This concludes the article.)
RTL-SDR and SIGINT
The photo at left shows a 2.GHz panel Yagi (a directional antenna) that was installed on a field expedient 30-foot wooden pole that is stabilized with guy wires. It is for use with a RTL-SDR dongle and a laptop to detect the signals controllng the movement of line of sight (LOS) drones that would emanate from the direction of the most likely avenue of approach. Its range of detection would be greatest when placed above the top of trees. In the world of radio, ‘Height is might’.)
The link to the RTL SDR dongle and the software for the RTL SDR, that can be downloaded for free, can be found at the manufacturer’s website.
A communications station in a bucket can be used as a part of a remote station located on key terrain (a hill) that overlooks the area and can be used for Signals Intelligence (SIGINT). This will likely be the most valuable intelligence collection method in the future, and it would be wise to learn how to develop intelligence to the best of our ability, as opposed to simply collecting information, or simply maintaining visual situational awareness. The process involves asking the most pertinent questions and using signal interception as a means to answer the questions posed.
Scanners Versus RTL SDR
Scanners have a well-known function that provides greater situational awareness, and can be a tool for developing intelligence. Signals Intelligence goes beyond situational awareness, and should be employed as it is needed to direct our defenses. Using a laptop with an RTL SDR dongle takes our situational awareness, and the ability to develop intelligence to a much-needed higher level as large swaths of the RF spectrum are visually represented on a screen in a waterfall display with spikes indicating the intensity of the RF. A directional antenna can provide a rough line of bearing. The RTL SDR dongle can also be used for detecting drones and other RF signals instantaneously. It can see very weak signals that can not be heard by an intercept receiver. Thus, it is a visual and audio all-mode extreme wideband receiver.
Detecting Drones and Their Controllers
Most commercial drones use the 2.4 GHz band for direction control as the downlink, and 5Ghz as the uplink. It is my understanding that we should be looking for the stronger uplink sent from the controller. The signal needs to be a strong one least the drone travels out of range of the controller. The longer the range of the drone, the stronger the signal needs to be to control its movement. An omnidirectional antenna can be used for 360-degree awareness, and a directional antenna can be used to detect wi-fi and drones at much greater distances. I would point a directional antenna in a direction in the most likely avenue of approach if the location was remote. The antenna should be located above the tree tops as these extremely high frequencies are easily attenuated by foliage.
If living in a remote location on the edge of wilderness, and given that RF at the extreme high frequencies of 2.4 and 5 Ghz, these signals are short range. Any RF activity detected by the RTL SDR above a baseline could indicate drone or wifi activity. The 2.4GHz yagi antenna greatly increases the sensitivity and range of detection, perhaps up to 5 miles LOS in ideal terrain conditions, or above the tree tops where drones would fly. I wil be doing more testing with this in the future with an inexpensive drone.
The 2.4GHz yagi greatly increases the potential range of detection from the weaker signal on the downlink from the drone, perhaps up to several miles LOS in ideal terrain conditions. Foliage will reduce the range of potential detection to several hundred yards. The receiving antenna must be above the trees to be effective. If the drone was nearby, the Yagi would have to be rotated to track the drone and it would probably be difficult to track. A yagi would be most helpful when detecting drone activity from a distance. An omnidirectional 2.4 Ghz and 5 Ghz antenna is likely the better choice for most situations.
The 5 GHz signal would be the strongest signal as it would emanate from the controller. However, in a pine forest, the controller could be located behind a stand of pine trees that soak up the signal. It would be best to be looking at the 5 GHz band with the RTL SDR to determine the Line of Bearing with a yagi, and the location of the controller. Locating a station where the antenna is above the tree tops where drones would fly would greatly improve the odds of early detection of both the drone or the controller, so that a warning could be issued in time for persons to seek a hiding place. More testing with this will be done in the future with an inexpensive drone.
FLdigi
While the terms used are unfamiliar, and perhaps intimidating, it is relatively simple, and there is plenty of technical support found on YouTube, and elsewhere. FLdigi has for many years been used on the Amateur HF bands. It is essentially text messaging over High Frequency (HF, shortwave) Amateur Radio frequencies. And this day stream can be used to send photographs. It is currently an unconventional practice to use one of the 150 digital modes on FLdigi over VHF/UHF transceivers. Because of the many digital modes, and because they sound similar, or unfamiliar, except for the popular modes in Amateur Radio circles, it is difficult for civilians to identify all the different modes. The data burst can be shorter or longer depending upon the digital mode that is used. At the left is a screenshot of FLdigi. This software offers a selection of many different and similar digital modes that are typically used over HF frequencies. These same digital modes can also be used over VHF/UHF frequencies as a method of text messaging.
Choose the most reliable mode, typically one with a slower rate of transmission, so that the receiving station receives a good copy. Other modes that offer faster rates of transmission can be used when the signal is stronger and the background noise is at a minimum. Better antennas can improve the signal-to-noise ratio, and support faster data transfers. Use of brevity codes also shortens the transfer time. Strive to keep the data transfer under 5 seconds by breaking up lengthy texts into parts. Thus, it would be difficult to intercept, and decipher, as the opportunity to identify the particular mode used is fleeting. Using encryption, however, is not permissible over the Amateur bands.
AndFldigi is a lightweight version of FLdigi for the Android tablet. The Skywave Linux software comes with a full complement of Amateur Radio software including those important to the article, namely: FLdigi, RTL SDR, and CHIRP. (The latter is used for radio programming.) Both are free to download from the Internet. Skywave Linux 3.1 is light enough to run on older and slower laptops. It can be dual-booted alongside any Windows operating system. With spare bootable USBs with Skywave Linux, any decent laptop can be used. Many older laptops that ran Windows 7 have fast enough processors to run it virtually, or as a replacement operating system. This makes older computers that were inoperable due to viruses, functional once again by booting Skywave Linux 3.1. Rebooting with new a operating system will wipe the hard drive clean, and the computer will run as if it were new. Running it virtually means any laptop can be used to run this operating system on a temporary basis without altering the existing OS. Older and slower-processor laptops, and tablets can be acquired inexpensively in quantity, and be stored in Faraday cages as a part of the logistics base for several communications stations.
Plus a Cable
We will also need to get a good K-1 cable that is available for about $19 each from Baofeng Technologies (BTech). With just free software, an inexpensive cable, an inexpensive radio, and an old laptop or tablet, we are in business. Using a low power transmissions through a directional antenna, with a brevity code, or a One Time Pad, with transmission bursts of less than 5 seconds, and we have achieved a high level of COMSEC. And if someone is also mobile, the level of COMSEC is the highest. If we are not mobile, then transmitting remotely over field phones is the next best way to reduce the odds of becoming located via direction-finding methods. As always, use low power with a directional antenna, and terrain masking if possible. Take note that even though we believe we are using just about unbreakable encryption, we can establish a routine that can allow others to learn much about us. This is an effective technique that professional SIGINT Traffic Analysts (TAs) refer to as “patterns of life”. It is a serious threat. While as preppers, we cannot study the electronic battlefield like the SIGINT pros of the NSA and its partner agencies in the military, we can learn how to operate to avoid being profiled by avoiding routines.
FLdigi could be used on a common frequency that uses primarily voice, and where threats from local and relatively unsophisticated interceptors have only traditional scanners to monitor. Thus, they would not recognize a digital transmission for what it actually is. Only in rare instances may they possess a low-tech fox-hunting level of RDF capability that in the real world is a very time-consuming method when a signal is only intermittently available. SIGINT efforts can be thwarted if we remain wary, diligent, and disciplined. In such a world without the rule of law, when and where our nation has become a failed state/ And consider that the use of FCC satellites to locate radio transmissions is unlikely in the vast majority of situations, as it is even currently, because such assets are far too valuable to use on low-value targets. The demand to monitor cell phone traffic is overwhelming, and their primary task.
Here are a couple of links for further reading:
Closing Remarks
This article was geared to those who are acquainted with radio, yet are uncertain about what to do to improve their commo plan. The “commo in a bucket” concept can be applicable to any situation as it does not have to stay in a bucket. The bucket contents can be a communications package that is the heart of a home-based communications station, or any other station needed. Its content mirrors what could be found in an Amateur radio operator’s ‘radio shack’, and can be taken beyond that.
The DIY approach is in the spirit of what was once the heart of Amateur Radio, where individuals, out of necessity, made some of their equipment and maintained it. In the future austere settings that we envision, more severe than the Great Depression, we will have to adapt and overcome by innovating with what is at hand. We will, out of necessity, have to maintain our communications stations on our own, doing the best we can with what we have. Of course, we can presently buy what is needed, so stock up. Practice now to acquire the knowledge and skills that make it possible to stay on the air during the dystopian future we anticipate. It is the skills that will be more important than the equipment. We can always acquire another transceiver, and make the best use of it, because we have the knowledge and skills to do so. We cannot simply “buy one and be done.” Rather, we must acquire the requisite experience and knowledge now by using it now.
BTW, most of what I have learned and presented here was not learned by being involved in mainstream Amateur Radio.
Just get out there and do it!