RF receiver noise floor and SNR in high-performance spectrum monitoring

For spectrum monitoring systems, the role of the RF receiver is to capture signal transmissions in their purest form so key data can be extracted by third parties for analysis, decoding, and demodulation.

This blog examines radio receiver noise floor and SNR as part of an RF spectrum monitoring solution for military, defense, and national security operations.

RF receivers in military operations

As military operations become increasingly volatile, commanding officers must make critical decisions quickly based on accurate and up-to-date information.

From communication systems on the ground to radar equipment and drones, dynamically detecting and geolocating RF signal sources using powerful spectrum monitoring tools provides a tactical advantage. RF Receiver performance is critical to this process.

RF receivers must be designed to sweep a wide swathe of RF spectrum from HF to mmWave. Additionally, they should be able to process transmissions with a wide dynamic range in real time and with high signal fidelity to provide vital Signals Intelligence (SIGINT) for swift and actionable decision-making.

Spectrum monitoring receivers are fundamentally different to test receivers and are used to perform the following tasks:

• Detect unknown signals in unknown environments
• Search for illicit activities over the entire EME
• Monitor specific frequency ranges to identify patterns and trends
• Measure spectral characteristics of intermittent/random signal bursts
• Flag an alert after detecting an unrecognized signal
• Demodulate, decode, process, and transfer signals
• Geolocate signal sources

What factors are critical for best RF receiver performance?

Multiple factors affect RF receiver performance. Intrinsic parameters of the receiver itself, such as radio architecture, IBW, noise figure, linearity, phase noise, and sweep speed, are critical in the system design or procurement phase. Secondly, external factors such as RF interference, antenna placement, and receiver position will affect receiver performance in the deployment and operational phases.

When setting up spectrum analyzing equipment on the front line or in command-and-control offices, it is important to consider the location of the equipment in relation to other wireless-enabled technologies being used. This is because the RFI generated will directly impact receiver sensitivity and, ultimately, the fidelity of the captured data.

System design and configuration will also impact sensitivity levels. The biggest challenge, however, is capturing a signal in its purest format. To ensure this, any deployed solution must optimize the RF signal to noise ratio to ensure important SIGINT is not missed.

The importance of noise floor

To extract the levels of data needed for accurate SIGINT, RF signal strength should be as high as possible relative to the noise level (the noise floor). This may be achieved by increasing the signal level and minimizing the noise level. If the RF signals are too weak relative to the noise floor, then a wealth of potentially critical information will go undetected and, more crucially, untraceable. The loss of such vital intelligence could ultimately compromise military operations.

What affects the noise floor?

Noise floor is determined by the intrinsic parameters of the radio receiver itself, and on top of this is added noise from external RF interferers (RFI), including jammers. Conflict zones change very quickly, and adversaries will leverage RFI to disrupt and interrupt communications channels, damage military equipment, and implement other covert tactics.

Special operational forces hunting for adverse RF activities require agile spectrum monitoring equipment with highly sensitive RF receivers and a high dynamic range, allowing them to detect, track, and geolocate transmitters whose signals may only be received just above the noise floor. This makes it possible to obtain mission-critical information. 

The importance of wideband RF reception

Attempting to identify the unknown is another challenge for the military and defense forces. They need a signal-agnostic system that can search for unknown signals in a wide frequency range so that new sources can be identified, demodulated, and decoded in real time to support insightful decision-making.

A 9 kHz to 40 GHz RF receiver, for example, enables real time monitoring of multiple frequency bands, including handheld trunked radios and RADARs. Similarly, a 100 MHz instantaneous bandwidth (IBW) capacity allows for a more comprehensive and detailed analysis of frequency hopping signals.

The need for lightweight, rugged (yet highly sensitive) RF receivers 

Lightweight, transportable, and compact RF monitoring systems deployed for military, defense, or national security operations can be easily packed and redeployed. Operators can also benefit from RF monitoring systems that function autonomously in harsh, remote locations, either collecting data in isolation or in a mesh with several receivers to provide comprehensive coverage. Good systems also include the processing power to enable real time signal processing at the receiver, as well as backhaul links to allow receivers to combine for missions such as TDOA.

RF monitoring systems with highly sensitive receivers, combined with skilled placement to minimize interference and maximize wanted signal strength, give military forces a tactical advantage by allowing them to detect, measure, and monitor RF signals quickly. By monitoring the RF spectrum 24/7 and distinguishing recognized transmissions from illicit or hostile ones, it is possible to determine for these signals:

• Who or what is generating them
• Where they are coming from (geolocation)
• What countermeasures are needed

Conclusion

In military and defense operations, most tactical operations rely heavily on wireless communication and electromagnetic attacks. Powerful spectrum monitoring systems with highly sensitive receiver capabilities are integral to detecting RF transmissions, monitoring adversarial communication activity, and obtaining greater situational awareness for effective decision-making.

RF receivers must offer high-performance specs, including a wide tuning range, high sweep rate, low noise figure, and high linearity. The receivers must each be mounted in the best practicable position with the best antenna placement to minimize interference and maximize wanted signal strength. The combination of a high-performing receiver with skilled positioning gives the best chance of capturing RF signals with sufficient fidelity to be useful.