Datasheet

A GUIDE TO RF SIGNALS
7 | TEK.COM/RSA
Identifying signals you measure with a spectrum analyzer can be difficult even with
the best of tools. The radio spectrum is a shared resource and the propagation
characteristics change for each frequency band.
What follows are some guiding principals about radio transmissions. When you find
a signal of interest, whether this is signal that should or should not be present in a
particular frequency band, you would want to start with the basics.
The first step is to look at the frequency, bandwidth, and shape of a signal of interest to
get an idea about the characteristics & therefore the identity of this signal.
For example, many of the 3G and 4G signals have square tops due to the type of
filtering they use. Also, these commercial wireless signals use predicable bandwidths.
You can make an educated guess on the signal type based on what you see on the
screen.
Other signal types will have different information bandwidths and different filtering
employed, therefore they will have a different shape on the Spectrum Analyzer display or
the Real-Time display of an analyzer.
The second step is to perform modulation analysis of the signal. Analyzing the
modulation will give further insight into more of the unique characteristics of a signal.
The fastest, simplest, and most common way of doing this is to take advantage of a
spectrum analyzer’s Audio Demodulation feature – to play the FM or AM audio out the
instrument of the signal of interest. Your ear can hear differences in signals.
There are limitations using this method, for example the Audio Demodulation of an
analyzer may have a much smaller bandwidth compared to the signal of interest
bandwidth. However, there are often distinguishable sounds from various signals seen
throughout the spectrum, and this method is a proven technique to help identify signals.
The third step is to capture the signal data and perform additional analysis of the signal.
This can be a difficult technique because based on some experience, trial and error
would be used within the RF measurement software capabilities to try to determine
more characteristics of the signal. For example, you could look at the RF IQ vs. Time to
try to figure out a digital modulation Symbol Rate, or look at the Spectrogram to try to
check for the presence of OFDM subcarriers.
SIGNAL CLASSIFICATION 101
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Amplitude
Time Domain
Measurements
Time
Frequency
Frequency Domain
Measurements