TN_IDA_1068_E_IQ_data
4 / 8
Subject to change
Figure 5: Simplified block diagram of NRA and IDA for
recovering the IQ data. From the A/D converter
onwards, it corresponds to the receiver structure
shown in figure 3
Table 1: IQ data handling facilities of NRA and IDA
cos(
ω
ν
t +
φ
ν
)
A
D
cos(
ω
0
t)
-sin(
ω
ν
t +
φ
ν
)
Recovering the IQ data: How it is done in NRA and IDA
NRA and IDA combine analog and digital techniques for signal analysis:
a classic heterodyne receiver for pre-selection is followed by a digital
analyzer for fine selection and further processing. To help you
understand IQ data recovery, the block diagram can be simplified as
follows:
Following pre-selection, frequency conversion, and A/D conversion, the
received signal is mixed down to a base band and split into its in phase
and quadrature components in the process. The subsequent filters limit
the bandwidth. It should be noted here that the frequency of the IQ
demodulator can only be roughly selected because the exact signal
frequency is unknown; the phase is initially arbitrary. Generally, too, the
selection filter does not correspond to that used in the correct receiver,
as the filter parameters are also not known at this point in time. The
parameter settings merely serve to allow the part of the spectrum of
interest to be saved as IQ data.
There are basically two modes for storing the IQ data: block mode and
streaming mode.
A maximum 250,000 points per block are available in
block mode
. The
maximum bandwidth here is 32 MHz. NRA and IDA capture the data
block by block, i.e. take sections from the time signal. Time gaps in the
recording thus occur between the blocks. The advantage of block mode
is the high bandwidth.
In
streaming mode
, the NRA captures the data continuously and
outputs them without interruption via one of the interfaces. The
maximum bandwidth is 400 kHz. The advantage of streaming mode is
that the data are without time interruptions. The limitation of the
bandwidth to 400 kHz is a disadvantage.
D
isplay
Demo
dulate
Store intern
al
ly /
SD c
ard
Block m
ode
Streaming m
ode
IDA
• •
•
1)
•
–
NRA
2)
–
–
•
•
1)
Export using IDA-Tools or on SD card
2)
With NRA demo program
