Application Notes / SparkWave AR 18/23G
Ensuring radio path clearance is a constant practical problem in microwave
radio path engineering. Line-of-sight between two antennas is necessary
but in many cases path clearance cannot be directly ensured. Several
solutions to overcome this problem are well known: implementation
of relay stations, passive repeaters or two back-to-back antennas.
- A relay station is the most expensive solution. This
is reasonable in the case of (radio-relay) RR network nodes if
an add-drop possibility is expected.
- The most commonly used solution is a passive repeater.
The main disadvantage of a passive repeater is the high installation
price and limited range of incident angle. If the incident angle
increases, the necessary reflection surface increases as well.
Large surfaces are inconvenient in both cost and ecological aspects.
- The third possibility is two back-to-back connected antennas.
This solution is applicable in the case of one of the terminal
stations being close to the repeater (up to a few hundred meters).
This application note deals with the possibility of implementation
of a lesser-known solution: the active repeater. The Iskra Transmission
SparkWave AR 18/23G active repeater was found to be one of
the most price effective and reliable solutions. Hundreds of devices
been installed since 1999 and they are still operating without any
A short description of the SparkWave AR 18/23G active repeater
The SparkWave 18/23AR active repeater is a proprietary solution of
Iskra Transmission. It was primarily developed as an optional device
for the family of SparkWave DRL 18/23GA (18 and 23 GHz frequency range)
radio-relay systems, but it can also be used in combination with the
equipment of other producers. It consists of a microwave module (antenna
branching units and two wideband microwave amplifiers with automatic
gain control) and two antennas for both directions. One of the two
antennas can be mechanically bound with the AR module, while the second
one is connected to the AR module by flexible wave-guide. The received
signal from both sides is amplified by two amplifiers and transmitted
in the opposite direction at the same frequency.
The low power consumption of the repeater (1.3 W) makes solar cells
a possible power supply. The solar cells have a lifespan of more than
20 years. Batteries assure 30 days of autonomy even in the case of
damage to the solar cells or continuous shade. Normal daylight without
direct sunlight is sufficient to supply the device and charge the
The advantages of an active repeater are:
- The amplification of active repeater is independent of the incident
angle (0 to 180°). High performance (directive) antennas enable
enough isolation between both antennas for sthe stability of repeater
operation. Both antennas can operate on the same polarization.
- The signal amplification enables establishment of a long-haul
transmission system - a chain of active repeaters can be used
for this purpose.
- A price-effective solution
- Quick system set-up
- Active repeaters can be much smaller in comparison to passive
repeaters, so they are also suitable for ecologically sensitive
Active Repeater layout
Questions arising during AR planning
Position of the AR between two terminal stations
- transmission quality with regard to the position of the AR between
two radio terminals
- number of active repeaters connected in the chain
Let us assume 40 km radio path length is bridged with one active repeater
AR. Simulated distance from the active repeater AR and the terminal
station is 1 km, 5 km, 10 km and 20 km.
- High performance directive antennas were chosen. The antennas
diameter (gain) is fitted to the hop length (between 0.8 and 0.3
- Transmitted power of SparkWave DRL 18GA: +16 dBm
- Transmission capacity: 34 Mbit/s (B=24 Mbit/s)
- AR output power +13 dBm (automatic gain control between 43 and
- During fading, maximum amplification of AR is 62 dB.
The subject of simulation is calculation of the flat fade margin
(BER = 10-3) for different positions of AR.
During simulation, in addition to the signal amplification, thermal
noise of the AR in channel bandwidth (B=24 MHz) must be taken into
account. Both, the receiver noise and the transmitted AR noise will
cause the receiver threshold degradation.
The simulation results are illustrated in the following diagram.
In case where AR is close to the terminal station, transmitted AR thermal
noise at the SparkWave DRL 18GA input will dominate. Due to high level of
the receiver input signal, the transmission quality remains nearly the
same compared by the case of transmission without the AR. In case where AR
is in the middle between terminal stations, thermal noise of SparkWave DRL
18GA will dominate and the thermal noise of the AR will be negligible.
The transmission quality and availability will be increased.
The chain of active repeaters
Active repeaters can be connected in the chain and long haul connection
can be established. The number of successive AR's is limited due to accumulated
noise of the AR along the chain.
|SparkWave DRL 18GA transmitted power
|Antenna gain (0.8 m)
|AR noise figure
|Channel bandwidth (34 Mbit/s
|Hop lengths between AR
|CNR for BER=10-3
As can be seen from the diagram, eight hops by AR will decrease FFM
(flat fade margin) for 8 dB. The number of successive AR is dependent
of required transmission quality and availability. Designer must optimize
each case separately.
The implementation of Iskra Transmission SparkWave DRL 18/23AR active
repeater was found to be one of the most competitive and reliable solutions.
Many hundreds of devices have been installed since 1999 and they continue
to operate without troubles. Long haul transmission systems can be implemented
by using a chain of active repeaters. Low price, quickly set up, incident
angle independence and ecological aspects are the main advantages of