So what IS an RTSA?

You mean - what IS a Real Time Spectrum Analyzer?

Oscilloscopes display signals in the time domain (voltage against time), and some have quite insensitive FFT capabilities too for frequency information. But spectrum analyzers are dedicated units that display signals in frequency domain (amplitude against frequency). This allows users to track signal levels and phase noise, as well as identify unwanted signals and their frequencies. 

As RF bands get increasingly crowded, engineers are expressing a need to examine frequency bands for available channels, as well as identifying interference sources. For intermittent noise sources you really need real time spectrum analysis - not an analyzer that takes time to do a frequency scan.

Real time spectrum analyzers (RTSAs) offer an almost instant real-time indication of the RF environment without waiting for lengthy sweep/scans. This means you can now catch short-burst GSM signals, FHSS transmitters, and intermittent spurious signals.

The Spectran V5 Series of Real Time Spectrum Analyzers. These analyzers  provide 20GHz scans in less than 20mS at a price point much lower than competitor models. This line of analyzers is fully customizable, with various optional upgrades, accessories, and frequency ranges, allowing you to “mix and match” to build the perfect real time spectrum analyzer kit for your test and measurement application.

Below is a handheld RTSA, but rack-mount and USB-connected versions are available:

SPECTRAN V5 Handheld Real Time Spectrum Analyzer shown with optional Locking Frames accessory.