RF Record and Playback Systems: Enabling Real-World Signal Analysis and Emulation
Overview
RF record and playback systems are essential tools for capturing, analyzing, and emulating complex, real-world radio frequency environments. They allow engineers to record RF signals directly from live scenarios such as open-air ranges, radar test chambers, and operational missions, and replay them later for analysis and validation as well as system development, enabling deep insight into system behavior. These capabilities are critical for electromagnetic spectrum operations (EMSOs) where systems must identify, classify, and respond to a dense and dynamic signal environment. Radar validation, EW system characterization, signal intelligence (SIGINT), and GNSS resilience testing all rely on accurate signal reproduction. Record and playback systems enable engineers to capture field signals for repeatable lab testing, recreate mission scenarios to evaluate algorithm performance, correlate a system’s transmitted and received waveforms, or conduct offline analytics such as channel modeling or emitter classification.
The underlying technology required to successfully build an RF record and playback system is complicated yet conceptually simple—capture, store, and replay. Executing this process at wide bandwidths, high fidelity, and multichannel scale introduces significant technical challenges. These systems are invaluable in scenarios where live signal environments are complex, unpredictable, require additional offline processing, or are difficult to replicate in a lab setting. This white paper will briefly explore the architecture of an RF record and playback (RPS) system and examine some of the design challenges and considerations for building one.
Contents
System Architecture
It is useful to break a basic record and playback system into three parts: the receiver or recorder, data storage, and the transmitter.
Figure 1. Basic record and playback system
The receiver captures the RF signal of interest. Signals of interest, both pulsed and continuous, for RF recording applications are wide ranging from friendly or neutral forces such as GPS/GNSS to threat signals such as those used for jamming or spoofing. After the signal has been captured and recorded, an engineer can go back to their lab for further offline analysis. Deep analysis on reliable recorded signals is important in applications like signal intelligence as well as channel modeling and channel sounding. Doing channel sounding and creating accurate channel models is critical in wireless communications. New spectrum requirements for 6G and the expansion of non-terrestrial networks (NTNs) are driving the need for new channel models in more commercial use-case systems. Additionally, aerospace and defense organizations are requiring more mission‑critical testing and modernization of military platforms.
In the case where RF playback is needed—and not just offline processing—after the signal is recorded, it’s played back using a transmitter. RF playback is useful for the following common applications:
- Stimulation for a device under test
- Signal source during product development
- Channel emulation
Design considerations for the receiver and transmitter include bandwidth and data throughput, system size and cost, phase coherence and synchronization, and scalability and flexibility.
Many systems on the market today are limited to 1 GHz or less of instantaneous bandwidth, often supporting only a single channel. For modern systems, this constraint prevents complete environment capture. Recording even 1 GHz of I/Q data at full resolution can require sustained write speeds nearly 5X (MB/s) the signal bandwidth. Maintaining lossless throughput at these rates across multiple channels quickly outpaces the capability of conventional storage and streaming architectures.
Selecting the right RF transmitter and receiver is important, but selecting and configuring the data storage in an RF record and playback system is the most difficult part. Data must be written to disk fast enough to capture the signal and ensure that no bits are lost in the process, either because of insufficient disk write speeds or insufficient ability to transfer data from the ADCs of the receiver to a hard drive. For small bandwidth signals, these challenges are not typical; but for RF signals, the amount of data that must be stored is significant. The following formula shows how to calculate the data rate in bits per second required to write to disk for a signal.
Data Rate [bits/sec] = Sample Rate [Sample/s] * ADC bitness [bits/Sample]
However, for RF applications normally the NI-RFSA fetch function gets I/Q data as 16 bits regardless of the ADC bitness. For RF signals I/Q data should be treated separately resulting in the following rates:
- 16 bits of I data per sample = 2 bytes
- 16 bits of Q data per sample = 2 bytes
- All together: 4 bytes per I/Q sample
Based on these calculations, the equation for total data rate will be the following formula:
Data rate [bytes/sec] = IQ rate [sample/sec] * 4 [bytes/sample]
This will mean if you have 100 MS/s IQ rate, it will result in a 400 MB/s data rate.
There will be cases when you will have only RF bandwidth information. The relationship between IQ rate and bandwidth is the following:
Bandwidth = IQ rate * 0.8
Which means:
IQ rate = 1.25 * bandwidth
So, the equation for total data throughput will be the following:
Data rate = 1.25 * bandwidth * 4
So
Data rate = 5* bandwidth
This calculation means if you have 100 MHz of bandwidth, you will have a 500 MB/s data rate. If you need to record extended amounts of time or larger bandwidth signals, the data requirements grow quickly.
Solid state drives (SSDs) are a good choice for writing data quickly and can be a requirement for recording wide bandwidth signals. RAIDs provide a good option for storing large amounts of data, either from wide bandwidth signals or long record times. A final option to consider is preprocessing the data before it is written to disk to reduce the amount of data that needs to be stored. For example, you might choose to run an FFT and store the frequency domain data instead of storing the raw data. FGPAs provide the processing speed required to do this step. This option will not work for all applications, but for others it is a good solution.
The NI Solution for Record and Playback
The NI RF Record and Playback (RPS) system addresses common challenges with a modular, software-defined, and phase-coherent architecture designed specifically for demanding environments such as aerospace and defense test environments. Built on the PXI platform, the NI RPS combines instrument-grade RF transceivers with high-speed data movement, synchronized timing, and advanced system compensation software.
The NI RPS supports up to 4 GHz of instantaneous bandwidth and multichannel streaming at rates up to 40 GB/s. Engineers can record or play back raw I/Q data across multiple channels without data loss, even enduring long-duration captures. Configurable allows for up to 300 TB of system storage, enabling hours of full-rate recording.
For radar, EW, and direction-finding applications, channel-to-channel coherence is critical. The RPS synchronizes all transceiver channels by sharing LOs, reference clocks, and triggers across the system.
Conclusion
RF record and playback systems are powerful tools for bridging the gap between real-world RF environments and laboratory testing. As spectrum environments grow denser and more dynamic, the ability to accurately capture and reproduce real-world RF scenarios becomes a mission-critical enabler, especially in mission-critical fields. These complex systems will play a pivotal role in enabling accurate analysis, robust product development, and reliable performance validation. Engineers can leverage this advanced technology to accelerate validation, improve repeatability, and ensure spectrum dominance across all domains.