NARDA NRA Series Technical Note

Narda Remote Spectrum Analyzer, NRA Series
Interference and Direction Analyzer, IDA Series
Technical Note TN101
Capturing IQ data with
NRA and IDA
A brief theoretical outline with
practical examples
With the Scope/IQ option, the NRA and IDA instruments allow you to
generate IQ data from the received data and display, demodulate, and
store them, and transmit them block by block or as a continuous stream
via a remote interface. What, though, is the significance of this I/Q data?
What are they used for? And, how are they obtained using NRA and
IDA?
Communications systems
To transmit data wirelessly it must be modulated onto a suitable, usually
high frequency, carrier signal. This gives a basic setup as shown in
figure 1. The demodulator must perform exactly the opposite function to
the modulator. The receiver must also be able to cope with the
impairments to the modulated signal that are added as it passes through
the communications channel.
The type of modulation has to be suitable for the signal content and the
communications channel. Various techniques are used to transmit
different signals together through the same medium and then separate
them again, e.g.:
 Frequency multiplex,
 Time multiplex and / or
 Code multiplex
The following types of modulation are commonly used for sinusoidal
carriers:
 AM, FM, PM, (angle modulation) for analog signals
 ASK, FSK, PSK, APSK, QAM for digital signals
If a prominent but unknown signal in the spectrum is to be classified or
even its message content reconstructed, various parameters such as
TN_IDA_1068_E_IQ data
Communications
channel
Modulator
Transmitter
Figure 1: Basic setup for a communications system
See last page for abbreviations
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Demodulator
Receiver
Subject to change