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EFA-T – characteristics
The test receiver, fully compatible in
all its functions with ETS300744,
receives, decodes and analyzes DVB-T
signals. All essential parameters for
demodulation of the receive signal can
be selected automatically or manually:
• Bandwidth 8 MHz, optionally
6 MHz or 7 MHz
• COFDM modulation with 2K or
8K FFT
• QPSK, 16QAM or 64QAM
constellation
• Code rate 1/2, 2/3, 3/4, 5/6,
7/8
• Guard interval 1/4, 1/8, 1/16,
1/32
• Hierarchical demodulation
= = 1, 2, 4
EFA-T – test reference for DVB-T
The newly developed Test Receiver
EFA-T features a multitude of innovative
measurement functions right from
the basic version, making it a test reference
for the systematic detection and
analysis of failures and disturbances
in the transmission channel (several
international patents pending). Apart
from total analysis, for example of bit
error rate (BER), detailed analyses of
freely selectable carrier ranges of the
OFDM signal can be performed. These
include:
• Constellation diagrams
• Calculation of transmission
parameters
• Display of modulation error ratio
(MER) as function of frequency
• Presentation of eye aperture as
function of frequency
Any failures and disturbances already
appear in the display of all carriers of
the OFDM signal. They can then be
accurately localized by narrowing
down the carrier range (see FIGs 3 to
8). A particularly effective method here
is presentation of eye aperture as a
function of frequency (FIG 5). What it
means is that the I and Q values are
shown together with the decision
thresholds, revealing any transmission
errors at a glance and allowing disturbed
carriers to be identified.
Investigations have shown that transmission
errors (BER) are attributable
often to only a few carriers while most
carriers are decoded correctly.
Detailed analysis is possible by means
of constellation diagrams of previously
identified single carriers.
EFA-T – operating principle
(FIG 2)
First the receive signal is conditioned for
the OFDM demodulator. Three slots for filters
of 8 MHz (optionally 6 or 7 MHz)
bandwidth are available in the receive
section for band limiting.
Noise can be superimposed on the receive
signal by a built-in noise generator and
associated attenuator. The C/N ratio is
entered directly thanks to a level meter for
both the wanted and noise signal.
Down-conversion to the second IF is followed
by passive analog lowpass filters,
the signal then passing to an A/D converter
with 12 bit resolution (fixed-frequency sampling
without oscillator tracking).
The digitized signal is then applied to the
synchronization, digital complex mixer, FFT,
channel estimation, error protection and
MPEG2 processing stages.
After channel estimation, the I and Q components
are coupled out for the constellation
diagram and calculation of further
transmission parameters and taken to the
DSP section. This directly drives the display
controller, which results in extremely fast
graphical processing of measured results.
FIG 2
Operating principle of EFA-T
Control bus
Receive
section
Level
meter
AGC 1
SAW
f IF,1 = 36 MHz
8 (7/6) MHz
Noise
generator
LPF
AGC 2
f IF,2
A
D
OFDM
demodulator
DSP:
Constellation
analyzer
Parameter
analyzer
I/Q (f)
MPEG2
measurement
decoder
(optional)
Osc.
f OSC
f CLK
MER (f)
FFT
2/8 K
Channel
estimation
Inner
de-interleaver
Viterbi
decoder
Other
de-interleaver
Synchronization
Reed-
Solomondecoder
Energy
dispersal
MPEG
interface
Display
controller
NCO
FEC
News from Rohde & Schwarz Number 164 (1999/IV) 5