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13 GHz/11GHz MICROWAVE RADIO STATION
The 13GHz/ 11GHz microwave radio station equipment is one of the
series of digital microwave equipments currently in production line of ITI. It
specifically caters for medium capacity digital transmission interconnection
local exchange in a city. The equipment operates in the frequency band of
12.750 GHz to 13.250 GHz and is designed to carry 480 PCM voice channel
data on a single radio frequency bearer channel. Simultaneously, a maximum
of 8 radio frequency channels consisting of 7 working and one protection
channel can be equipped.
SALIENT FEATURES FO THE EQUIPMENT
· Capable of transmitting and receiving simultaneously,
1. 480 PCM voice channel data traffic corresponding to 34.368 Mb/s HDB-3
2. Two omnibus / express orderwire (analog) channels with selective
calling facilities for link maintenance.
3. Extensive remote supervisory system.
4. Switching information.
· Automatic switch over for 7 working and one protection channel.
· The equipment is fully solidstate and employs microwave integrated
circuits, dielectric resonators, oscillators and high speed digital
integrated circuits for high reliability.
· Radio transmission with QPSK modulation.
· Operates from a station supply of 48v DC with positive terminal
· Space diversity receiver with IF combiner as a counter measures
against the deep flat fading over the hop.
· Transversal equalizers as a counter measure against in band amplitude
and delay distortion caused by frequency selective fading.
The block schematic of 13GHz/11GHz (1+1) frequency diversity
Microwave radio station configuration expandable upto (7+1) configuration
is as shown:
The 34.368 Mb/s data in HDB# format from external multiplex
equipment is applied to switch over (SWO) module where the signal is
attenuated by approximately 3 db and is then divided into 2 routes
respectively to be supplied to transmitter digital processor (TX DPU)
module of regular (REG) and protection (PROT) channels. The TX DPU
facilitates Bi-polar to uni-polar (B-U) conversion, serial to parallel (S_P)
conversion, insertion of frame pattern, parity check information and switch
signals into two transmitting data streams of 19.332Mb/s each. The data
stream is scrambled and sent to the phase modulator (PH MOD) module of
transmitter (TX) unit.
In the PH MOD module, each of the two 19.338 Mb/s data streams are
differentially encoded and low pass filtered for shaping the pulse stream.
The pulse streams thus shaped are applied to two 0-pi modulators. A 70
MHz IF carrier is generated at the 70 MHz oscillator and split into the two
carriers for each 0-pi modulators. The phase difference between the two 70
MHz carrier is pi/2 radians. In each 0-pi modulator, the phase of carrier 70
MHz is modulated to a 0 phase or a pi phase by input pulse streams. The
output of the two 0-pi modulators are thus combined for four phase
assignment onto a 70 MHz carrier and IF amplifier and sent to the
transmitter radio frequency (TX RF) module of the TX unit at an output
level of ś3 dbm.
A L M MS /
P D U
MS / RS
P D U
P D U
P D U
SY ST E M B A SE P L A T E
In the TX RF module, the modulated IF signal is mixed with an RF local
signal from VCO to produce the transmitting frequency and is passé
through a 5-section band pass filter (5 BPF)
which allows only the
desired RF signal. The RF signal from 5 BPF is amplified upto the specified
value by GaAs FET amplifier in the FET AMP module and the signal thus
amplified is sent through the respective branching circuit. The FET AMP is
provided with an ALC circuit to stabilize the transmit output signal by
compensating for the variations of the signal due to temperature etc.
The RF input signal coming from the associated branching circuit
is applied to the receiver radio frequency (RX RF) module of receiver(RX) unit,
which also consist of delay equalizer (DEL EQL), receiver intermediate
frequency (RX IF) and transversal equalizer (TRSV EQL) (optional) modules. In
the RXRF module the received RF signal is amplified by a GaAs FET low noise
RF pre-amplifier, which has a low noise figure of max. 4.5 db and is mixed
with an RF signal of the local oscillator and converted into a 70 MHz band IF
signal and the local IF signal is amplified by the pre-amplifier to the required
In the case of space diversity receiver (SD RX) which consist of space
diversity radio frequency (SD RX RF) and IF combiner (IF COMB) modules ,
the RF is input signal applied from the associated SD branching circuits to
the SD RX RF , is mixed with an SD local signal from the main RX. Then the
RF input signal with an SD local signal from the main is converted into a 70
MHz band IF signal. After amplification it is applied to IF COMB. The IF
COMB monitors the phase difference between the main and SD IF signals.
And when detects a phase difference between the 2, the local signal phase
of the SD receiver is shifted by the endless phase shifter (EPS) of the SD
RX FREQ CONV module to make the two phase coincide. The voltage sum
of IF signal from the main receiver are combined in-phase by an IF hybrid.
The IF signal is then applied to the DEL EQL module, which equalizes
group delay caused by the branching filters. The equalized IF signal is
filtered by RX IF module and amplified to a constant output level of ś3dbm
by automatic gain control(AGC) ckt. The IF signal then passes
The phase demodulator (PH DEM) modules consist of four phase
demodulator circuit where the input IF signal is split into two paths and the
applied to has detector ckt‘s where information is detected by coherent
detection. The HDB3 signal from receiver digital processor (RX DPU) is
then, fed to SWO modules, where one of REG and PROT is selected by the
control signal for passing on to external multiplex equipment.
The pilot generator/ pilot detector (PG/PD) consists of PG/PD
circuits. The pilot generator generates a 34.368 MHz signal and encodes a
pilot signal pattern. The PG section consist of TX PROT access switch over ckt
that selects either transmitting protection access signal or pilot signal by TX P
access switch over control signal. The PD converts the receiving bipolar pilot
signal into a uni-polar signal and decodes the signal to detect a pilot signal
pattern. The PD section is composed of RX PROT access switch over ckt,
which leads the receiver pilot signal to a PD ckt and the receiving protection
access signal to the output terminal by switch over operation.
The Alarm Control (ALM CONT) module outputs the alarm and control
signalsto the external equipments. Alarm signals, monitored in each
respective module and control signals are gathered at the AMT CONT
module for concentrated processing according to use.
SUPERVISORY AND CONTROL SYSTEM
The service channels (SC) unit for 34 Mb/s digital microwave radio
system provides the following facilities through analog service occupying
the band 0.3 to 12 KHz.
a) Remote supervision and control (4.3 to 7.4 KHz band)
b) Omnibus orderwire telephone circuit (0.3 to 3.4 KHz band)
c) Express orderwire telephone circuit (8.3 to 11.4 KHz band)
To ensure satisfactory maintenance operation of radio relay communication
system, the sc UNIT is classified into the following three types:
1) SC/MS: Service channel unit equipped with supervisory and control Master
2) SC/ RS: Service channel unit equipped with supervisory and control
Remote Station facility
3) SC: Service channel unit without supervisory and control facility.
A 4 wire operation telephone panel (TEL) is mounted on SC unit for
two channel use with a channel selection switch, a hand set and selective
calling facility. The in band DTMF (dual tone multi frequency) system is used
for selective calling facility.
The SC unit includes remote supervisory and control facility, which
employs microprocessor control logic circuit design. The remote station
module can report upto 32
Supervisory items & can receive upto 8 remote control items. The master
Can monitor and control upto 8 station śconsisting of 7remote stations and
master station it self-by the polling method. The supervisory control Signal is
transmitted using FSK signal, which is assigned in 4.3 to 7.4 KHZ band of
Analog service channel.
The Analog Service Channel (ASC) signal occupying the 0.3 to 12 KHZ
band is inserted to both the regular and protection channels. The drop of ASC
is normally made from the regular channel and if it become faulty, the drop
will be switched to
the protection channel.
SWITCHOVER CONTROL SYSTEM:
The Switchover control system (NAL) which has a capability of
switching up to 7+1 systems, provides automatic and manual control function
to prevent the traffic from interruption hen one of the regular channels fail due
to out of frame, bit error rate (BER) degradation or loss of signal etc. it
provides the switchover control function for RX switching. A switchover
control signal arranged in digital service channel is transmitted together with
main signal stream.
Automatic switchover to the protection channel is carried out when
any one of the regular channels fails. Automatic switching operation is
initiated from the NAL at the receiving end of the switching section. The radio
equipment at receiving end informs NAL of its channel according to the
1. A fault in the regular channel is detected at the receiving end. The
protection channel must be ready for service.
2. The faulty channel switching control signal is transmitted from the
receiving end to the transmitted end.
3. The above control signal is decoded at the transmitting end and the
transmitting end switch (TX SW) is controlled to the disconnect the
line drive (radio pilot pattern) signal from the protection channel
and transmit the incoming regular channels signal on both the
regular and protection channels.
4. The protection channel does not receive the line drive signal and in
frame condition of regular channel signal transmitted over the
protection channel is detected at the receiving end.
5. RX switching from the regular channel to the protection channel is
The Automatic switching mentioned above, however, automatically
restores to the original state upon recovery of the defective channel. if two or
more regular channels fail at the same time , this equipment controls the
highest priority regular channel and it will be switched over to the protection
channel. This switching priority can be arranged simply by setting priority
The equipment is built in a slim rack of dimension 120mm (W) x
225mm (D) x 2500mm (H) to utilize minimum floor space. Each radio
transmitter receiver is built in one rack, switch over control equipment is built
in one rack and supervisory equipment along with antenna port , Wave guide
& input power switch(NFB)are equipped in one rack. Thus a (1+1) system is
equipped in four slim racks.
13 GHz 34 Mbs radio Relay System Works in conjunction with the
· Antenna: 13 GHz high performance antenna with dual Linear polarized
feed. The size of the antennas is decided by the route engineering &
vary from 1.2meter to 2.4 meter.
· Waveguide run: Elliptical waveguide with UBR 120 flange is used as a
· Digital PCM MUX: Digital PCM MUX to CCITT specs consisting of 2Mb/s,
8Mb/s and 34Mb/s data from voice frequency.
· Station battery supply: the13GHz 34Mb/s equipment operates from ś
48v DC supply with positive grounded.
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