Radio Direction Finding

Manual Direction Finding

Once you have the equipment, you need to know the skills. So, how does manual RDF work and what are the steps? To illustrate it, I’ll use the following scenario:

You’re part of a group with three separate elements operating together: two patrol units and one command unit. The command unit is in a fixed or semi-fixed position, possibly vehicle-mobile. From their location, they’re running a signals collection system using SDR receivers and a laptop. A digital common operating picture is not available, so CalTopo Desktop is being used locally at the command post. Each patrol unit has been issued paper maps generated from CalTopo to ensure navigation and coordination can continue without digital support in the field.

Command’s SIGINT station intercepts a transmission from an opposition force communicating with their own command element. You and your sister patrol element are alerted and instructed to take bearings from your respective positions to locate the transmitting station, which is broadcasting on a frequency of 147.250 MHz.

While one member of your team confirms your location using a GPS, you attach your Yagi antenna to an HT and tune to 147.250 MHz. With the antenna extended, you slowly rotate until you receive the strongest signal, focusing on maximum signal strength. You then identify a terrain feature in line with the antenna and use your compass to shoot a bearing. Your unit’s RTO reports both your position and the bearing to Command. Meanwhile, the other patrol element follows the same procedure from their location to help triangulate the signal source.

Command, now in possession of both patrols’ positions and their relative bearings to the signal source, can plot the intersection points. Is this the exact location of the transmitter? Maybe not. Remember beam width — a 20-degree beam may seem narrow at close range, but it widens significantly over distance. The result is a zone of probability, not a pinpoint. Gathering more readings from different positions improves accuracy and narrows the search area.

Once you have a reasonable idea of where the opposition is, command can direct the nearest team into the area to fix and finish the opposition.

Find the intersection of the bearing lines to start to get a general idea of where the source of the radio signal is.

Points of Failure

Before we get into TTPs for mitigating RDF being used against you, it’s important to cover a few environmental factors that can interfere with your ability to accurately direction find a transmitting station. First, there are basic radio propagation concerns. Not all DF stations may be able to receive the transmission at all, which makes fixing a position much more difficult. Propagation can be influenced by several variables, including temperature, terrain, and the amount of vegetation in the area — especially when working with VHF and UHF signals, which are more easily blocked or absorbed.

Second, and more common in urban or suburban environments, is signal reflection causing multi-path transmission. In these cases, DF stations may not be receiving the direct signal from the actual source but instead picking up a reflected signal. This can create a false bearing, as the radio waves bounce off buildings or other structures.

Knowing the beam width of the antenna, we can use sectors to give a better understanding of where the source of the radio signal could be.

Practicing RDF

Increasing your chances of success in any endeavor comes down to training for it. One effective method is participating in, or hosting, a fox hunt. Radio fox hunting, also known as radio orienteering, is a recreational event popular among amateur radio operators. The setup is similar to a land navigation course, but instead of navigating by terrain alone, participants must locate a series of waypoints by homing in on low-power radio beacons. It’s a fun and practical way to sharpen your manual RDF skills under realistic conditions.

Many of these events are open to the public and can be found listed on websites such as homingin.com. They’re a great way to practice the skills needed for manual radio direction finding. If you’re part of a mutual assistance or civil defense group, it’s also a good idea to run scenario-based exercises together. Integrating RDF TTPs into your group’s regular training helps ensure that everyone knows how to work as a team and effectively use all available resources when it matters most.

Using bearings to shoot a center line down the arc of the sector can help us narrow down the likely location inside the more general search area.

COMSEC: Defense Against the Dark Arts

In the preparedness community today, it’s become trendy to claim that using unencrypted civilian radios like a Baofeng will get you “killed in the streets” or targeted by an airstrike if SHTF. The usual solution offered? An expensive, digital, encrypted radio. But want to know a secret? If you abuse or misuse those tools, they’ll get you killed in the streets too, just with a higher price tag. At least you’ll have looked good on Instagram before things went sideways. Gear matters, but discipline, training, and smart use matter a whole lot more.

RDF is simply a form of traffic analysis, which means that even encrypted communications are not inherently secure. Encryption protects content, not presence. However, by applying proper radio field craft, you can significantly improve your communications security (COMSEC) and reduce the risk of detection or interception.

Avoid Detection

An ounce of prevention is worth a pound of cure. If your transmission isn’t detected in the first place, no one knows to come looking for you. You can reduce the chance of detection in several ways.
Start by limiting your transmission power. Use only as much output as needed to complete the communication. For example, full-power VHF transmissions with full-size antennas are a poor choice for tactical comms between squad members. Instead, use low-power settings and stubby antennas to reduce signal range. This is especially effective in dense vegetation, where propagation is already naturally limited.

Selecting frequency bands based on their propagation weaknesses can also work in your favor. For example, VHF tends to refract more in urban environments, making it harder to pinpoint, while UHF is more easily absorbed in rural terrain and dense vegetation, limiting its range.
When communicating over longer distances, such as back to a fixed base, use directional antennas. This requires solid land navigation skills, similar to RDF, but the narrower beam reduces the chance of interception. It also allows you to use less power to complete the transmission effectively.

If you have a general idea of where potential adversaries might be located, you can use key terrain features to your advantage. Vegetation, hills, and other natural barriers can help block or weaken line-of-sight transmissions, making it harder for others to receive your signal or determine your position. Tools like the Viewshed Analysis feature in CalTopo are excellent for planning this ahead of time and identifying terrain that can help shield your communications from unwanted direction-finding efforts.

Be Nimble

While avoiding detection is ideal, it’s not always practical. You may find yourself operating “behind the lines” during a civil disorder scenario, or up against an opponent with multiple fixed or mobile automated RDF systems. In these situations, time becomes your most critical asset. Staying on the move is key.
Keep transmissions short and direct. Don’t linger on the air. Using pre-established code sheets for complex but commonly repeated messages can save valuable time. This applies even if you’re using encrypted radios, because the goal here isn’t just secrecy — it’s minimizing how long your signal is exposed to detection.

If you can communicate asymmetrically, even better. Digital modes like JS8Call allow you to transmit a text message that can be received and read later, giving you the advantage of minimizing transmission time. While often associated with HF radio, JS8Call can also be used on VHF and UHF bands with the right setup.

Once you’ve made your transmission, don’t stick around. Move away from your transmission point as quickly and quietly as possible to avoid detection and reduce the risk of being triangulated.

Be Pseudorandom

Even if you do everything else right, using a fixed check-in schedule increases the risk of being found. A consistent pattern gives your opposition a window to listen in, track, and eventually fix your position.
Instead, use a check-in schedule that appears random to outsiders but follows a predictable pattern known only to your team. This adds a layer of unpredictability that helps keep you off the radar. Alternating both frequencies and times further reduces the likelihood of someone identifying you or locking onto your transmissions. Randomness, when done with intent, becomes a powerful form of security.

A homemade Yagi antenna can be created quickly and inexpensively. Paired with a TinySA, it becomes a good manual RDF platform without having to rely on a traditional receiver.

What About Technical Countermeasures?

When it comes to technical countermeasures, the most effective is frequency hopping. This technique uses two or more radios synced to the same clock and set to follow a shared schedule, automatically cycling through frequencies during transmission. To the operators, communication appears uninterrupted. But to anyone trying to listen in, they’ll only catch a fraction of a second on each frequency before the signal jumps. By randomly cycling through channels, the chance of a successful intercept or direction finding attempt is significantly reduced. It’s a highly effective method for staying one step ahead.
While technologies like Frequency Hopping Spread Spectrum (FHSS) are common in military radios, they’re far less prevalent in the commercial and amateur radio world, though a few products exist. Unfortunately, no FCC-approved amateur radios currently support FHSS or Direct Sequence Spread Spectrum. Some commercial radios, like the Motorola DTR700, do offer these features, but they come with their own limitations and compatibility challenges.
The next major technical countermeasure is the use of Near-Vertical Incident Skywave (NVIS) setups with HF. While it is technically possible for national-level intelligence agencies like the NSA or DIA to conduct RDF against NVIS transmissions, doing so requires a level of sophistication and infrastructure far beyond the reach of most non-state actors. This makes NVIS a solid choice for secure regional communication, though it does require more planning, gear, and setup than VHF or UHF systems.

Conclusion

With simple tools and consistent practice, anyone can learn to conduct radio direction finding operations. While those with greater resources may opt for purpose-built, automated RDF systems, even individuals with modest means can get the job done using basic gear like directional antennas, paper maps, and a reliable compass. Skill matters more than the price tag.
Becoming proficient with your tools, along with the techniques, tactics, and procedures, takes time and consistent effort. Events like radio orienteering or fox hunting can help you build those skills more quickly in a controlled setting. Incorporating cat-and-mouse scenarios into your group training will strengthen your MAG’s ability to locate and fix transmitting stations. Just as important, it will help you develop the skills needed to protect your own communications against those trying to do the same to you.

Read More From Issue 69