Most of us in the RF & microwave world are familiar with spectrum analysers but what’s the difference between a real time spectrum analyser (RTSA) and a more traditional swept-tuned instrument? The clue is in the name and a swept-tuned analyser sweeps from left to right displaying measurement results sequentially i.e. not real time.

Inside a given span a RTSA displays the energy across all frequency components simultaneously. By using a FFT process and overlaying multiple FFTs in a staggered way rather than sequentially you get a gapless view and don’t miss transient signals. The processing power required for FFT means that it’s possible to obtain magnitude and phase information from the input signal as opposed to just amplitude with a traditional spectrum analyser. Also because the FFT process is taking information from the time domain and converting it to the frequency domain it follows that you can easily switch between frequency and time domains and look at changes in frequency over time.  All of this means the RTSA is ideal for evaluating communication signals or indeed any modulated signal as well as spectrum monitoring & RF device characterisation.

Just as an example of how complicated modern communication signals can be the below screenshot from the Narda SignalShark shows a commonplace 2 x 10 MHz LTE signal but there appears to be an interfering signal at 805 MHz.

 

In actual fact it’s an Internet of Things (IoT) signal designed to use resource blocks in the LTE signal. The persistence display of the SignalShark makes it very easy to spot apparent anomalies like this so if it truly was an interferer it would be quickly identified and could even be tracked down using the dedicated Direction Finding (DF) antennas available with the SignalShark.

The Narda SignalShark is a prime example of a modern RTSA. In a small hand held unit it has 40 MHz real-time instantaneous bandwidth and a 100% probability of intercept (POI) for signals longer than 3.125uS.