ETTC'2003 - SEE

ETCC'2003 European Test and Telemetry Conference
Δf: 5.5 kHz ±30%
maximum jitter in a character: 25%
Type of communication
two way, half duplex
Communication structure
Master (data concentrator) – Slave (meter)
Repeater mode:
Up to 7 repetitions – each node (meter) acts as a possible repeater
Antenna
External or internal
Power consumption
Pout=25mW at Us=3 V:
Rx=20mA at 3 V
Tx=70mA at 3 V
Pout=300mW at Us=3 V:
Rx=30mA at 3 V
Tx= 370mA at 3 V
Special focus has been put on extended temperature range, since due to price pressure, we
were not allowed to use special crystal. We have solved this problem by the microprocessorintegrated
option – real time temperature measurement and SW compensation of reference
frequency by a look-up table.
4. Test results
Several test were carried out during design phase, consisting in laboratory and in real
environment. We have found more or less the same problems and effects as known from the
RF theory. A lot of effort was spending to solve interferences problems that occur inside meter
itself. As the meter is powered by the mains power supply and since it must be with accordance
to several severe standard like IEC 1036, quite big insulation resistance between lines needed.
Long, wide lines with several rectifiers formed a mixer module with antenna. Transmitted signal
from integrated RF module mixed together with working frequency of a power supply and
transmit it in air. A receiver can see a resulting signal as AM modulated FM signal and as such
makes communication unreliable. The problem was solved by special design of PCB.
Some radio propagation and multipath effects were also found. The propagation of radio signals
is impaired by multipath interference. Multipath interference is present when the transmitted
signal arrives at the receiver following multiple propagation paths. The presence of multiple
propagation paths leads to fading and Inter-Symbol Interference (ISI) in the received signal.
Since radio signals propagate in all directions, the received radio signal is comprised of by a
multiplicity of (randomly) attenuated, delayed and phase-shifted replicas of the transmitted
signal. The superposition of these echoes causes random fading and broadening of the time
duration of the transmitted pulse (delay spread) that, in turn, leads to ISI in the received signal.
The presence of ISI means that subsequent symbols interfere with each other, thus leading to a
Bit Error Probability (BEP) floor that is independent of the SNR. A major difference between
indoor and outdoor propagation is that the former is much more sensitive to changes in the
geometry of the environment than the latter.
In a figure 7 we can see a detail from a test installation.