ARGUS in its core consists of an SDR-receiver mounted on a drone that is connected to a base station using a highspeed wireless network. The receiver currently in use is capable of continuous reception from 24 MHz up to 1.7 GHz spanning a wide range of services including licence-free radio services (PMR, CB), public safety, utilities, marine VHF, airband, amateur radio bands, telemetry and broadcast services, land mobile radio, low-power ISM devices and even cellular and satellite services.

Capabilities

1. Rapid geolocation by simply flying a few controlled bearings

With nothing more than the SDR waterfall and a couple of deliberate heading changes, the drone can produce multiple angles on a signal in a matter of minutes. This allows surprisingly accurate transmitter location without requiring any fixed infrastructure or multi-site setups.

2. Instant line-of-sight to signals that are completely hidden from any ground position

By ascending even modestly, the platform gains radio visibility into valleys, behind ridgelines, or into terrain-shielded areas. Many emitters that appear silent from the ground suddenly become fully observable once altitude compensates for terrain masking.

3. Direct RF observation inside otherwise inaccessible or private areas

Because the drone does not rely on ground access, it can overfly fenced compounds, industrial zones, remote huts, or private property and capture their RF activity profile without crossing physical boundaries. Even a simple spectrum view already reveals presence, timing, and signal types.

4. Large-area spectrum sweeps in a single flight using standard SDR tooling

Basic scanning software is sufficient to collect broad RF activity footprints across entire mountain regions or rural landscapes. A stationary setup would require days of repositioning to achieve the same level of coverage that a single flight can produce in minutes.

5. Detection of remote or low-power field equipment the moment line-of-sight is achieved

Telemetry bursts, small UHF links, isolated sensors, and mountain repeaters become immediately visible once the drone clears local obstructions. Even minimal RF output is enough for detection when the receiver is elevated and free of ground-level multipath.

6. Indication of individual presence through uplink activity in remote or shielded environments

From an elevated position, the system can observe short uplink bursts from personal devices that would not be detectable on the ground due to terrain, low power or distance. These brief transmissions act as a general indication of individual presence in remote, shielded or otherwise inaccessible locations

Hardware

The DJI Mavic Air 2 serves as the carrier platform for the ARGUS payload. With a lifting capacity of over 500 grams it's a good choice to deploy such a system.

Hardware:

Raspberry Pi Zero 2 W
Geekworm X306 V1.3 UPS-shield with 1x 18650 Li-Ion battery
Airspy Mini SDR-receiver
LIWEARE Dual-band WiFi Adapter

Ground hardware:

Ubiquiti router with sector panel or beam antenna (Litebeam M5, Nanostation M2 Loco)
Used to establish a high-speed wireless network connection using either 2.4 or 5 GHz WiFi to transmit the SDR datastream.

The hardware is mounted on a light, custom designed and 3D-printed (PETG) plate using a GoPro-like mount that allows a quick payload replacement.

⚠ SAFETY AND LEGAL WARNING ⚠

1. Compliance and Certification
Always operate in accordance with all national drone regulations. Any modification not specified by the manufacturer will invalidate type certifications and operating licenses. Operating an uncertified aerial vehicle may also void your insurance coverage for any resulting damages.

2. Safety Hazards of Modifications
Modifying critical components like weight and center of gravity outside of manufacturer specifications can lead to unpredictable flight behavior and a complete loss of control. This significantly increases the risk of a crash, which can cause serious property damage and severe personal injury.

3. Radio Frequency Compliance
You must always adhere to national frequency allocation laws. When using third-party WiFi antennas, it is your responsibility to ensure full and continuous compliance with ISM regulations (e.g., transmit power, antenna gain). Note that unauthorized reception of certain frequencies may be illegal in your jurisdiction.

Payload Antenna Setups

The following section describes antenna setups currently in use and their characteristics.

HTOOL SL10 Mini UWB Log-Per (50 kHz - 3 GHz)

This ultra-wideband log-periodic directional antenna is a solid allround-solution and easily spans the complete reception range of the SDR receiver. On higher frequencies, where the directionality of this antenna is more pronounced, it can be used to read bearings and direction find transmitters.

Dualband (VHF/UHF) Normal-Mode Helical

Used for omnidirectional reception of the VHF and UHF bands. The radiation pattern of these normal-mode helical designs are almost isotropic and well-suited for this use case.

VHF/UHF Magnetic Loop Antenna (75-240 & 310-490 MHz)

Extremely narrow bandwidth. Must be finely tuned on-frequency prior to deployment. Can't be used for wideband measurements.
Excellent for use in highly congested RF environments, e.g. near transmission towers.
Pronounced directionality when tuned on target frequency which allows for compact sub-GHz direction-finding.

SMA Attenuation Set

In case of high field strengths - for example when searching for a hidden transmitter in close proximity - attenuators can also be used to avoid receiver overload.

Currently 10 dB, 20 dB and 30 dB are available for use. All connected together will attenuate signals by a factor of 1 million.

However, it has not been tested yet where the limitations of the Airspy Mini are in regards to direct signal injection, which would render attenuators useless at some point.

WiFi Link Antenna Setups

The WiFi-dongle used can connect third-party antennas using an SMA-RP jack. Operation in accordance with national ISM-regulations must be ensured at all times!