2310 RWA.ib RWA_ib RWA Ib

User Manual: 2310-RWA_ib

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I R T Electronics Pty Ltd A.B.N. 35 000 832 575
26 Hotham Parade, ARTARMON N.S.W. 2064 AUSTRALIA
National: Phone: (02) 9439 3744
Fax: (02) 9439 7439
International:
+61 2 9439 3744
+61 2 9439 7439
Email: sales@irtelectronics.com
Web: www.irtelectronics.com

IRT Eurocard
Type RWA-2310
Reverse Path Amplifier
Telstra serial items:
347/99 RWA-2310
347/105 Manual for RWA-2310
347/106 FRU-2300
347/108 PSU-2300

Designed and manufactured in Australia
IRT can be found on the Internet at:

http://www.irtelectronics.com

2310-rwa.ib.doc

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08/07/2002

IRT Eurocard
Type RWA-2310
Reverse Path Amplifier
Instruction Book

Table of Contents
Section

Page

General description
Technical specifications
Technical description
Pre-installation
Operational safety
Installation
Maximum limits
Power supplies
Connections
Front & rear panel connector diagrams
FRU-2300 Eurocard RF module frame
Operational safety
Modules & PSU’s
PSU-2300 DC input PSU
Maintenance & storage
Warranty & service
Equipment return
HFC Cable TV Network Overview
Forward path
Reverse path
Application of the RWA-2310 in reverse path systems
Drawing index

3
4
5
7
7
8
8
8
9
10
11
14
14
16
18
18
18
19
19
20
21
22

This instruction book applies to units later than S/N 9612000.

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08/07/2002

General Description

0 - 20 dB
ADJUSTABLE
ATTENUATOR

BLOCK DIAGRAM
REVERSE PATH AMPLIFIER
TYPE RWA-2310
INPUT

20dB COUPLER
24 dB AMP

MUTE
RELAY

INPUT
MONITOR

20 dB COUPLER

75 Ω

OUTPUT
MONITOR

2 WAY
SPLITTER

ISOLATED
OUTPUTS

75 Ω

The RWA-2310 has been designed to provide amplification of signals in the reverse path of cable TV distribution
systems.
An input attenuator with a 20 dB range provides gain control to optimise signal levels at the output.
The frequency response of the amplifier is tailored to give optimum low noise amplification to the reverse path
signals which normally lie between 5 and 100 MHz.
In addition the RWA-2310 is constructed with a high level of RF shielding which eliminates both ingress and egress
of unwanted RF signals.
Two types of frame are available for the RWA-2310 to suit different types of application:
The FRU-2300 allows 10 RWA-2310’s to be mounted in one 3 RU frame together with two PSU’s which
may be either 240 Vac or -48 Vdc.
The FRU-2310 allows 2 RWA-2310’s to be mounted in one 1 RU frame together with an inbuilt single
240 Vac PSU.

Standard features:

2310-rwa.ib.doc

•

2 - 200 MHz frequency response specially contoured for use in reverse path of cable TV
distribution.

•
•
•
•
•

Very low noise.
0 - 20 dB variable input gain control.
Local or remote muting.
Input and output monitoring on front panel.
Power loss alarm output.

Page 3 of 22

08/07/2002

Technical Specifications
IRT Eurocard module
Type RWA-2310
RF:
Input:
Type
Number
Impedance
Return loss
Maximum input level

DC coupled.
1.
75 Ω.
> 16 dB (2 - 200 MHz).
> +50 dBmV.

Outputs:
Type
Number
Impedance
Return Loss
Isolation between outputs
Maximum output level

DC coupled.
2.
75 Ω.
> 18 dB (2 - 200 MHz).
> 20 dB (2 - 200 MHz).
>+50 dBmV at 200 MHz.

Monitoring outputs:
Input monitor:
Impedance
Level
Output monitor:
Impedance
Level

AC coupled.
75 Ω.
-20 dB
AC coupled.
75 Ω.
-20 dB

Performance:
Gain
Frequency Response
Noise

Noise (f = 200 MHz)
CTB (22 channels Vo = 47 dBmV)
CSO (22 channels Vo = 47 dBmV)

0 to +20 dB. Adjustable from front panel.
2 to 200 MHz (-0.5 dB points).
-3dB frequency is typically 340MHz.
6 dB at maximum gain
-67 dB
-67 dB

Connectors

BNC

Power requirements
Power consumption

28 Vac or +28 Vdc.
<300 mA

Other:
Temperature range
Mechanical

Finish:

Front panel
Rear
Case

Dimensions
Optional accessories

2310-rwa.ib.doc

0 - 45° C ambient
Mounts in IRT 19" rack chassis types FRU-2300
(10 modules in 3 RU*) or FRU-2310 (2 modules in 1 RU).
* Maximum number dependent on air circulation - See
installation section of manual.
Grey enamel, silk screened black lettering & red IRT logo
Bright steel.
Alodine finished aluminium.
30 mm x 3 U x 231 mm IRT Eurocard
Instruction manual

Page 4 of 22

08/07/2002

Technical Description
(For detail see diagram 803947)

Signal Path:
BLOCK DIAGRAM
REVERSE PATH AMPLIFIER
TYPE RWA-2310

20 dB
ADJUSTABLE
ATTENUATOR

[0 dB]
INPUT

[-20 dB]

[-40 dB]

20dB COUPLER
[+0 dB]

+24 dB AMP
INPUT
MONITOR

OUTPUT
MONITOR

20 dB COUPLER

RL1
[-20.5 dB]

[+3.5 dB]

75 Ω

[+3 dB]

75 Ω

2 WAY
SPLITTER
[-3 dB]

ISOLATED
OUTPUTS

[+0 dB]

[-16 dB]

The block diagram for the signal path shows the basic layout of the amplifier and its inputs and outputs. The figures
in square brackets indicate the approximate signal levels at various points in the circuit when the amplifier is set to
unity gain.
The input signal is taken directly to a variable attenuator (maximum 20 dB) whose control is accessible through the
front panel of the module.
The attenuator output is connected to the 24 dB gain amplifier via a coupler, which provides a monitoring BNC
connector on the front panel with a signal of approximately -20 dB relative to the amplifier input.
This signal may be used to ensure that the signal at the input of the amplifier is sufficiently low as to avoid
overloading. The best level will depend on the number of carriers present in the signal and the desired operating
level for the system as a whole.
The amplifier output is connected to the output splitter via a muting relay operated switch, which terminates the
amplifier output and splitter input in 75 Ohms. This allows the output of the amplifier to be muted if a signal with
excessive noise is present which may cause problems for other equipment downstream.
The output of the amplifier is monitored immediately prior to the passive output splitter so as to not introduce a
variation in loading between outputs. When measuring output levels using this monitoring point it should be
remembered that the actual output level of the amplifier will be 3 dB lower at each output connector in addition to
the 20 dB loss in the coupler.
Due to the output splitter being of a passive type it is also essential that both outputs always be terminated in 75 Ohm
loads. If one output is not used a termination plug should be fitted to that output.
Amplifier gain. Each coupler itself introduces approximately 0.5 dB of loss in the signal and the output splitter
introduces a further 3 dB loss so that with the overall losses exclusive of the attenuator total 4 dB. The amplifier gain
is therefore chosen to be 24 dB so that the gain range overall is 0 to 20 dB.

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08/07/2002

Alarms and controls:
General alarm.
This alarm is generated whenever the output of the amplifier is not active due to either loss of
power or muting.
When no power is present the normal position for relay contacts RL 2 is with a connection to ground indicating the
alarm condition.
When power is applied and no muting signal is present the low impedance of relay coil RL 1 allows the muting
control line between diodes D 9 & 10 to rise to nearly the full 24 Vdc power rail. This signal is used to turn on
transistor Q 1 which operates relay RL 2 and releases the grounding contact on the alarm output.
When a muting control signal is applied the muting control line falls to near ground and transistor Q 1 turns off
resulting in the RL 2 relay contacts closing to ground.
Muting.
The muting relay RL 1 may be operated either by the front panel switch or by remote contact closure
to ground. In its un-energised state the relay provides a connection between the amplifier and splitter and when
energised mutes the output.
The grounding control inputs from the switch and external connector are isolated by diodes D 9 & 10 which provide
an OR function. This means that whilst the amplifier may be muted by either means it is not possible to return the
amplifier to its normal operating mode unless both the front panel switch and the remote input are in the normal
setting.

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08/07/2002

Pre-Installation
Operational Safety:
WARNING
Operation of electronic equipment involves the use of voltages and currents that may
be dangerous to human life. Note that under certain conditions dangerous potentials
may exist in some circuits when power controls are in the OFF position.
Maintenance personnel should observe all safety regulations.
Do not make any adjustments inside equipment with power ON unless proper
precautions are observed. All internal adjustments should only be made by suitably
qualified personnel. All operational adjustments are available externally without the
need for removing covers or use of extender cards.

Pre-installation:
Handling:
This equipment may contain or be connected to static sensitive devices and proper static free handling precautions
should be observed.
Where individual circuit cards are stored, they should be placed in antistatic bags. Proper antistatic procedures
should be followed when inserting or removing cards from these bags.

Power:
AC mains supply:

Ensure that operating voltage of unit and local supply voltage match and that correct rating fuse
is installed for local supply.

DC supply:

Ensure that the correct polarity is observed and that DC supply voltage is maintained within the
operating range specified.

Earthing:
The earth path is dependent on the type of frame selected. In every case particular care should be taken to ensure that
the frame is connected to earth for safety reasons. See frame manual for details.
Signal earth: For safety reasons a connection is made between signal earth and chassis earth. No attempt should be
made to break this connection.

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08/07/2002

Installation
Installation in frame or chassis:
See details in separate manual for selected frame type.

Maximum limits:
The enclosed construction of the RWA-2310 gives excellent immunity to electromagnetic interference, but reduces
the ability of the electronics inside the casing to dissipate heat.
Adequate air flow should be ensured when modules are placed together in the 3 RU frame to prevent overheating
and premature failure of the modules.

Thermal budget:
A fully equipped FRU-2300 frame of RWA-2310’s with two PSU’s fitted will produce approximately 110 W of heat
output.
As a result the following rules should be observed:
1. Frame ventilation should not be obstructed by any equipment mounted immediately above or below the
FRU-2300. If possible a 1 RU blank panel should be mounted above and below the frame to ensure that
adequate air flow can occur.
2. No more than 8 RWA-2310’s should be mounted in an FRU-2300 when free air (unassisted) circulation is
the only cooling available or where the ambient temperature exceeds 30°C.
The RWA-2310’s should be mounted in the positions shown in the following diagram with front blank panels
type FB-700 fitted to the unused positions.
1

RWA2310

FB-700

RWA2310

FB-700

RWA2310

BLANK

PSU 1

PSU 2

PT-701
or
PSU-2300

3. All 10 positions in the FRU-2300 may be used when fan forced cooling is available in the rack and the
ambient temperature is controlled to less than 30°C.
4. The RWA-2310 should not be mounted in a frame above other equipment which has a high heat output
which will increase the effective ambient temperature to above 30°C.

Power Supplies:
When fitted to an FRU-2300 frame the RWA-2310 may be powered by either the PSU-3001 240 Vac PSU or the
PSU-2300 -48 Vdc PSU.
In either case it is recommended that two PSU’s be fitted at all times so that the power load is shared between the
two supplies. In the event of failure of one supply the amplifiers should function within specification whilst operating
on the remaining supply as long as the correct input voltage is held to within the specifications for that supply.
However it is not recommended that a full frame of amplifiers be operated on a single supply for an extended period.

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08/07/2002

Connections:
RF input: This is a single connector with a 75 Ohm input impedance and should be fed from a suitably
impedance matched source.
RF outputs: Two outputs are provided which are obtained by a passive output splitter.

It is recommended that the two outputs be loaded in 75 Ohm terminations at all times.
If one output is not to be connected to external equipment it should be fitted with a 75 Ohm termination plug. Failure
to observe this may result in a noticeable drop in performance in the output being used.
Mute input: The external mute input presents an open circuit voltage of approximately +24 Vdc and may be
operated by either a contact closure to ground or by an open collector transistor driver. The connection to this input
must be capable of sinking a current of at least 15 mA.
The mute input is connected from the 9 pin ‘D’ connector at the rear of the module via the frame motherboard to a
Krone IDC connector mounted on the rear of the frame for each module. Connection details are marked on the
frame.
Alarm output:
The alarm output makes contact to ground in the alarm condition and is open circuit in the
normal condition. The maximum rating on the relay contacts is 30 V (AC or DC) @ 500 mA.
The alarm output is connected from the 9 pin ‘D’ connector at the rear of the module via the frame motherboard to a
Krone IDC connector mounted on the rear of the frame for each module. Connection details are marked on the
frame.
9 pin ‘D’ connector:
The 9 pin ‘D’ connector provides connection to the selected frame for power supply inputs for either one or two
power supplies and for the alarm output and mute input signals.
This connector mates with a matching connector on the selected frame type and the necessary external connections
for the alarm and mute signals are made to the frame and not the module.
The following pin connection details for the 9 pin connector are therefore given for service and general information
purposes only.
Pin Connection
1
Gnd
2
AC 1 or DC +ve
3
AC 1 or DC -ve
4
No connection
5
Mute
6
AC 2 or DC +ve
7
AC 2 or DC -ve
8
Gnd
9
General alarm

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08/07/2002

Front & rear panel connector diagrams
The following front panel and rear assembly drawings are not to scale and are intended to show relative positions of
connectors, indicators and controls only.

RW A- 2 3 1 0

GAIN
INPUT

IN
OUTPUT 1

MONITOR
OUT

OUTPUT 2

OPERATE

MUTE
MUTED
DC
FRAME

N140

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08/07/2002

IRT Eurocard Frame
Type FRU-2300
General Description
The purpose of the FRU-2300 is to provide an economical and compact mechanical framing system for IRT 2300
series Eurocard RF shielded modules.
In addition the frame provides a power supply bus to reticulate power from one or two common low voltage power
supply units to all modules in the frame.
A total of ten 2300 series IRT Euro-modules and two power supply units can be accommodated in one FRU-2300
3 Rack Unit Frame.
A choice of power supply units is available to provide power from either AC or DC supplies. Each supply is capable
of supporting a full frame of cards on its own and AC and DC fed supplies may be mixed in the same frame.
IRT 2000 series Eurocard RF shielded modules are fully enclosed boxes designed to prevent the ingress or egress of
electromagnetic interference. The module is complete with front fascia panel and rear signal and power connectors
which provides the necessary connections to the frame PSU’s other equipment.
The module can be inserted or removed from the frame from the front. When inserted one connector on the rear
mates with a motherboard connector which carries the data and power supply connections.
Although the module may be inserted or removed from the front of the frame, care must be taken when doing so to
ensure that the connections to the rear of the module have sufficient slack cable for this to be accomplished. If this is
not the case all cables should be disconnected before attempting to remove the module from the frame.

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08/07/2002

Technical Specifications
IRT Eurocard frame
Type FRU-2300
Power:
DC

AC mains input (240 Vac ±10%)
and / or
-48 Vdc ±25%.

Input power fuses

AC
DC

SLO-BLO 500 mA.
Fused in PSU-2300 PSU module.

Output power to module bus:

28 Vac from PT-701
and / or
+28 Vdc from PSU-2300

Input power:

Connectors:
Modules
Power module to frame
Power input to frame
Alarm / control

AC
DC

DB female 9 pin RF filtered.
H15FP4 H15 female 4 mm PCB mounting.
IEC 320 with integral fuse holder.
Klippon MK 1/3 3 pin termination block 2616.
Krone IDC (1 per module).

Other:
Temperature range

0 - 50° C ambient.

Mechanical

3 RU (482 mm x 132 mm) standard 19” rack frame.
Suitable for mounting in standard 19" racks.

Finish

Natural anodised aluminium frame with bright
passivated steel side panels & rear power connection
box with black silk screened lettering.

Dimensions

482 x 132 x 285 mm (Frame empty.)
Clearance width 445 mm.

Optional accessories

PT-701 single power supply module 240 Vac input.
PSU-2300 single power supply module -48 Vdc
input.

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08/07/2002

Circuit Description
The FRU-2300 provides a circuit path to the modules for two complementary supplies and a ground earth reference
making a total of five busses. One supply buss pair is obtained from each of the two PSU module locations. Each
supply buss may be either AC or DC according to the type of power supply module selected.
The outputs of the two types of supply are floating with respect to ground.
In the case of the AC type supply this will result in a symmetrical output for the two AC busses due to the action of
the bridge rectifiers in the connected modules.
In the case of the DC type supply the negative side will rise to approximately +0.7 Vdc due to the action of the
conducting diodes in the negative side of the bridge rectifiers in the connected modules.
The ground supply buss is connected directly to the chassis, safety earth of the 240 Vac IEC input connectors and the
+ve side of the -48 Vdc input connector.
The power supply modules connect to the mother board via special H15FP4 connectors. This allows the modules to
be inserted or removed safely whilst power is applied to the frame inputs.
An alarm circuit is provided which connects to the two PSU’s. When operating normally the alarm is open circuit.
When supply is lost the alarm line is grounded.
When both PSU’s are installed a failure of either PSU will enable the alarm.
Connection to modules is made via 9 pin D connectors as described in the General Description.
Connector pin designations are as follows:
9 pin D Eurocard module connector:
Pins
Designation
1
Gnd.
2
AC/1 + or
3
AC/2 + or
4
No connection.
5
Mute.
6
AC/1 or
7
AC/2 or
8
Gnd.
9
Tally.
Special note:

2310-rwa.ib.doc

+32 Vdc/1.
+32 Vdc/2.
0 Vdc/1.
0 Vdc/2.

Whilst this frame appears at first sight to be similar to the FR-748A Eurocard frame for 700 &
3000 series Eurocards, there are major differences which make the two quite incompatible.
Please note especially that whilst the PT-701 PSU is able to be used in both the FR-748A &
FRU-2300 that the PT-748A PSU is incompatible and to safeguard against accidental insertion the
power supply contacts for the PT-748A PSU make no connection in the FRU-2300.

Page 13 of 22

08/07/2002

Installation
Operational Safety

WARNING
Operation of electronic equipment involves the use of voltages and currents which
may be dangerous to human life. Maintenance personnel should observe all safety
regulations. Do not change components or make adjustments inside the equipment
with power ON unless proper precautions are observed. Note that under certain
conditions dangerous potentials may exist in some circuits even though power
controls are in the OFF position.

Modules & PSU’s
FRU-2300 Frame:
Eurocard Module
Slide the module into its appropriate position and tighten the two retaining screws. If the module does not seem to be
fully inserted check that the module is not being fouled by any cables at the rear.
Rear Connections
Signal connections. These are made directly to the rear of the module. If it is desired to be able to remove the
module without accessing the rear of the frame to disconnect the cables it will be necessary to ensure that
approximately 300 mm of additional cable is provided, on each connection, which can readily be withdrawn through
the frame to a sufficient distance to disconnect at the front of the frame.
Data connections: These are made to a three way Krone IDC connector above each module. The three connections
are designated to suit the RWA-2300 reverse path RF amplifier module as follows:
Pin Connection
1
Mute - connected to pin 5 of the DB 9 module connector.
2
Tally - connected to pin 9 of the DB 9 module connector.
3
Ground - connected directly to chassis / PSU ground reference.

Power Supply
The frame will operate with either one or two power supply modules installed.
The power supply module should be slid into either slot 11 or 12 at the right hand end of the frame. The four
retaining screws on the front should be tightened.
Connect power input to rear of frame. For DC input; observe the polarity markings next to each connector.
Due to its weight if the frame is to be freighted for any purpose the power supply should be removed and packed
separately before shipment.

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08/07/2002

FRU-2300 Dimensional diagram
Note: Dimensions on this diagram are approximate only and do not take into account any connections at the front or
rear. Dimensions indicated are intended as a guide for cable installation purposes only.
436 mm

255 mm
285 mm

240 mm

132 mm

482 mm

The following diagrams are not to scale and are intended only to show relative locations.

FRU-2300 Front View

Module positions
1

PSU 1

PSU 2

FRU-2300 Rear View
12G

12G

FRU-2300 Frame
SLOT 12

SLOT 11

240 V 50 Hz
0.2 A

FUSES
500 mA S.B.
-48 Vdc INPUT

Module Positions
6
5
4

-48 Vdc INPUT

ALARM

S.347/66

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08/07/2002

IRT Power Supply for Eurocard
-48 Vdc to +29 Vdc
Type PSU-2300
GENERAL DESCRIPTION
The PSU-2300 is designed to provide complementary low voltage DC power supplies required for operation of up to
10 IRT RWA-2310 Eurocard modules.
The IRT PSU-2300 DC-DC converter converts a nominal 48V input voltage to +29V with respect to ground.
Two PSU-2300s can be operated redundantly when using an FRU-2300 Frame. The redundant power supply facility
of the PSU-2300 is enabled in each IRT RWA-2310 by having the power supply circuit of each module made up of
two bridge rectifier circuits with the outputs connected in parallel. This allows the +29 volts to be sourced from
either PSU-2300.
A front panel LED indicator provides visual confirmation of the presence of the low voltage output.
An alarm relay is also included which will activate the alarm if the output fails.
The PSU-2300 is available in -48 Vdc only and is not configurable by the user.

TECHNICAL SPECIFICATIONS
IRT Eurocard Dual Power Supply Module
Type PSU-2300
Power Requirements:
Voltage
Power
Fusing

48 Vdc ± 25% Positive ground.
1.5 A maximum.
2A

Output voltage:

+29V @ 2.8A

Connectors:

DC power input / output

H15MFAV32 male, Faston

Other:
Temperature range

0 - 50° C ambient

Mechanical

Suitable for mounting in FRU-2300 rack frame

Finish:

Front panel
Body

Dimensions

2310-rwa.ib.doc

Grey enamel, silk screened black lettering & red IRT
logo
Passivated steel with silk screened black lettering.
6 HP x 3 U x 230 mm

Page 16 of 22

08/07/2002

CIRCUIT DESCRIPTION
The PSU-2300 consists of a DC-DC converter circuit which provides a 29 Vdc output..
The DC input circuitry consists of a safety fuse followed by a low value series resistance and over-voltage
protection zener diode and a number of RF suppression components.
The front panel LED power indicator and alarm relay are powered from the output rail by way of a series zener
diode so that if the rail voltage falls there is insufficient voltage to operate the relay and the LED dims sufficiently to
indicate the fault condition.
The alarm is shown in the unenergised position. When operating normally the alarm is open circuit. When supply is
lost the alarm line is grounded.

INSTALLATION & SERVICING
FRU-2300 Frame:
The PSU-2300 should be slid firmly into either of the two double width slots (11 & 12) at the right of the frame. The
four retaining screws on the front should then be tightened.
Power to the PSU-2300 is supplied from a connector located on the rear of the FRU-2300 immediately to the rear of
the module. Care should be taken to observe the correct polarity as marked when connecting DC to this connector.
The alarm output connector is located on the rear of the FRU-2300 frame and is common to both supply units when
installed. The alarms for both units are in parallel such that when a fault develops in either PSU the alarm output will
be grounded.
WARNING - Each PSU-2300 dissipates up to 10 Watts and a full frame of ten RWA-2310s and two PSU-2300’s
dissipates nearly 100 Watts. Ensure that adequate ventilation is available to keep down the operating temperature. If
possible at least 44.5mm (1RU) should be left clear above each frame.

Internal adjustments:
The PSU-2300 is factory set for the correct output voltage and should not require re-adjustment unless one of the DC
- DC converters is replaced.
Adjust RV 2 for +29 Vdc

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08/07/2002

Maintenance & storage
Maintenance:
No regular maintenance is required.
Care however should be taken to ensure that all connectors are kept clean and free from contamination of any kind.
This is especially important in fibre optic equipment where cleanliness of optical connections is critical to
performance.

Storage:
If the equipment is not to be used for an extended period, it is recommended the whole unit be placed in a sealed
plastic bag to prevent dust contamination. In areas of high humidity a suitably sized bag of silica gel should be
included to deter corrosion.
Where individual circuit cards are stored, they should be placed in antistatic bags. Proper antistatic procedures
should be followed when inserting or removing cards from these bags.

Warranty & service
Equipment is covered by a limited warranty period of three years from date of first delivery unless contrary
conditions apply under a particular contract of supply. For situations when “No Fault Found” for repairs, a
minimum charge of $A100.00 will apply, whether the equipment is within the warranty period or not.
Equipment warranty is limited to faults attributable to defects in original design or manufacture. Warranty on
components shall be extended by IRT only to the extent obtainable from the component supplier.

Equipment return:
Before arranging service ensure that the fault is in the unit to be serviced and not in associated equipment. If
possible, confirm this by substitution.
Before returning equipment contact should be made with IRT or your local agent to determine whether the
equipment can be serviced in the field or should be returned for repair.
The equipment should be properly packed for return observing antistatic procedures.
The following information should accompany the unit to be returned:
1.
2.
3.
4.
5.
6.
7.

A fault report should be included indicating the nature of the fault
The operating conditions under which the fault initially occurred.
Any additional information which may be of assistance in fault location and remedy.
A contact name and telephone and fax numbers.
Details of payment method for items not covered by warranty.
Full return address.
For situations when “No Fault Found” for repairs, a minimum charge of $A100.00 will apply, whether
the equipment is within the warranty period or not.

Please note that all freight charges are the responsibility of the customer.
The equipment should be returned to the agent who originally supplied the equipment or, where this is not
possible, to IRT direct as follows.
Equipment Service
IRT Electronics Pty Ltd
26 Hotham Parade
ARTARMON
N.S.W.
2064
AUSTRALIA
Phone:
Email:

2310-rwa.ib.doc

61 2 9439 3744
service@irtelectronics.com

Page 18 of 22

Fax:

61 2 9439 7439

08/07/2002

HFC Cable TV Network Overview
Typical Hybrid Fibre - Coaxial Pay TV Distribution System
Over 100 nodes per
headend.

Free to Air
TV
Channels
Pay TV
Service
Provider
Pay TV
Service
Provider

600 to 1000
homes per hub.

Up to approximately
15 hubs per node.

Node

Hub

Node

Hub

Node

Hub

Splitter
Headend

Amp

Splitter
Set top unit
&
TV receiver

Splitter

Amp

Splitter

Amp

Splitter
Set top unit
&
TV receiver

The Forward path:
In a Hybrid Fibre Co-axial cable (HFC) network the forward path has a broadband RF capacity bandwidth from
approximately 85 MHz to 750 MHz. This wide bandwidth is due to the large requirements of the pay TV
application.
Signals from various program providers are concentrated at HeadEnds for distribution through the system on a single
cable or fibre connection. The input signals to the HeadEnds may be provided over baseband coaxial cable or fibre
optic links or in the case of free to air broadcast channels may be demodulated from a locally available signal off air.
These signals are modulated and combined to provide a single wideband multichannel signal for distribution.
From the Headend the signals are amplified and converted into optical signals for transport down dedicated fibres to
a node. Each node is strategically located to cater for approximately 10,000 customers.
From each node the signals are distributed to a hub which may service between 500 and 1000 customer sites. At the
hub the signal is converted form optical to electrical and amplified before travelling down a coaxial cable for final
distribution.
Currently the final distribution to the customer uses amplitude modulation (AM) for ease of interfacing with current
set top decoders.
In the final distribution via coaxial cable a combination of splitters and amplifiers is employed and in any particular
connection a total of three amplifiers may be present.
This forward path topology ensures that the highest quality of signal is maintained with very low noise by the use of
optical fibre transport technology until the final stage of distribution. From this point the high signal level allows the
signal to noise ratio to be maintained at high levels as far as the subscriber connection.

2310-rwa.ib.doc

Page 19 of 22

08/07/2002

The Reverse path:
Whilst the forward path provides an adequate system for distribution of programme material to subscribers it is
unidirectional due to the amplifiers and other active hardware in the system. Yet the fibre optic and coaxial cables
themselves are able to carry traffic in either direction and so the opportunity is presented to make a bidirectional
system which makes provides a better return on the investment in cable and fibre installation.
Provided the bandwidth is sufficient and the signal to noise ratio is kept high the reverse path can be used to provide
a wide variety of services which may or may not be related to the primary signals carried in the forward path.
Examples of such services are telephony, high speed data for computer access to the Internet, ISDN services,
impulse pay per view (IPPV) registration, movies on demand, home shopping and status monitoring and
control (SM&C). Each of these services requires a link back to the service provider.
Whilst IPPV and SM&C services contain only small amounts of information and are suitable for a polled service
occupying a minimal bandwidth of less than 1 MHz, telephony, Internet and ISDN require both a larger bandwidth
and are typically connected for quite long durations. In addition, Internet, ISDN and data modem services in general
require a low noise path in order to minimise date errors.
In order to provide such a reverse path it is necessary to overcome the losses introduced by the passive splitters in
the forward path and at each point of amplification provide a reverse path around the forward amplifier. In addition
it should be noted that whilst the forward path is a divergent system, and noise levels are relatively easy to control,
that the reverse path is convergent and so the noise from every source adds to that of every other across the whole
available bandwidth.
It is therefore important that the amplifiers in the reverse path have a controlled bandwidth response to exclude
signals in the forward path and that the intrinsic noise of each amplifier be minimal both in band and out of band. In
addition to low noise, high speed data services require a minimal group delay through the system and this must
therefore be taken into account at every point in the system.
Different types of reverse path amplifier are required at different points in the reverse path.
In the cables leading from the hubs; small reverse path amplifiers with directional couplers are required to be located
in the same housing as the forward path amplifiers.
At the hub the reverse path signal is separated from the forward path signal so that it may be converted to an optical
signal and sent back to each node on a separate fibre to the forward path. At this point the reverse path signal
occupies a bandwidth from 5 MHz to 65 MHz.
Due to the noise ingress into the hubs from the coaxial customer network it is not possible to sum all of the reverse
path signals from the hubs together at the node. So at each node the signals are first converted back from optical to
electrical form so that they may be combined by Frequency Division Multiplexing (FDM).
This method together with the associated out of band filtering results in minimum noise increase in the combined
reverse path signals.
Before combining the signals it is important that the levels be adjusted to compensate for varying path losses from
the different hubs and so variable gain reverse path amplifiers with monitoring points are required in each node
input.
In addition it is desirable to be able to mute the signal from any path where a failure has occurred causing the noise
level to rise to a level where it may cause interference with other signals and thus corruption of services being
provided to customers on other hubs.
At each node the reverse path signal is converted back to an optical form for transmission back to the Headend on a
separate fibre to the forward path.
At the Headend (or at a node if heavy usage is indicated) the reverse path signal is converted back to electrical form
and delivered to decoding equipment for analysis and routing of individual signals. Not all signals will be required to
be passed further than the Headend and others will be required to be routed into the public telephony network or to
individual service providers.

2310-rwa.ib.doc

Page 20 of 22

08/07/2002

Application of the RWA-2310 in the reverse path:
The RWA-2310 amplifier is a wideband low noise amplifier optimised for use with RF signals between 2 MHz and
200 MHz. The term reverse path amplifier arises out of its suitability for use in the reverse path of a cable TV
network although its use is not limited to reverse path applications.
Nodes:
The RWA-2310 is designed to be used in the reverse path immediately after the optical signal receivers where it is
required to boost the level of the signal to enable the various signals situated in the reverse path band to be split into
each piece of receiving equipment at the correct level.
In addition it provides signal monitoring at this point for identifying problems in particular node or hub feeds and a
muting facility to disable the output in the event of the line becoming to noisy to use.
HeadEnds:
At HeadEnds the received optical signals are once again converted from optical format to an electrical signal. The
RWA-2310 may once again be used to perform the same functions as at the nodes.
The reverse path signal at this point is processed by a computer controlled system which interprets the addressing of
the incoming signals and routes them to the appropriate destination, whether it be a pay TV provider, ISDN service
or Internet access provider.
The router for these signals requires that the signals from various sources be adjusted to the same level so that the
router output for a particular destination is held within the prescribed limits of the equipment which converts the
signal into the appropriate form for that provider.
General:
As the number of users of the reverse path grows, so does the number of amplifiers needed. The RWA-2310
provides an ideal solution to this expansion due to its modular nature. Additional amplifiers may be plugged in as
required into pre-wired rack frames.
It is also vital that in the event of any failure that maintenance is able to be carried out as quickly as possible. The
monitoring points on the RWA-2310 provide a ready access to the signals for locating faults and its modular nature
allows rapid replacement of a module should its performance be in doubt.
Dual power supplies with a choice of AC or DC options and external alarms enhance the reliability of the
RWA-2310 and the local and remote muting functions may be used to quickly isolate any source of noise in a given
path before it is combined with other signals to their detriment.

2310-rwa.ib.doc

Page 21 of 22

08/07/2002

Drawing Index
Drawing #
803947
803980
804039

2310-rwa.ib.doc

Sheet #

Description

RWA-2310 200 MHz Amplifier schematic
FRU-2300 Eurocard frame schematic.
PSU-2300 schematic diagram

Page 22 of 22

08/07/2002

PC803948

OUTPUT
MON

BNC

+24

R3
56R

C6
100n

1N4148

D10

R2
33R

+24

C5
100

C4
100n

R10
3K3

7824
U1
1

CPL1
20dB

LED1
PWR

+24

2
I

INPUT
MON

R12
10K

R13
33K

R9
3K3

LED 2
RF OFF

C3
100n

100n

2,3,7,8

AMP 1

+24

C1
1500

D12
1N4148

Q1
BC108

C2
1500

RL1

RL2

D11
1N4148

+24

R4
75

20dB
ADJ
ATTENUATOR

G
2

2
1

1
2

ATT1

RL1

5R6

R11

33R

D13
1N4148

+24

R5
75

D5-8
1N4004

D1-4
1N4004

1N4148

R6
56R

RL2

20dB

CPL2

1R8

2,3,4,7,8

PCS
2-1-75

SPL 1

FL4

FL3

FL2

FL1

FL5

FL6

SK1/7

SK1/3

SK1/2

SK1/6

SK1/1

SK1/9

SK1/5

SK1/8

BNC

ISOLATED
OUTPUTS

INPUT

1 19/03/96

2 23/04/96
3 20/05/96
4 15/08/96

ECR750
5 02/10/96

ECR861
6 17/06/97

CONTRACT No.

ENG. APP.

CHECKED

DRAWN

R.K.

803947

RWA-2310
REVERSE PATH
AMPLIFIER
DRAWING No.

TITLE

IRT Electronics Pty. Ltd.
ARTARMON NSW AUSTRALIA 2064

SCALE

SIZE

SHEET
1 OF 1

TB-1

SK1

3. GROUND

2. TALLY INDIC

1. MUTE CONTROL

SK10

TB-10

240VAC
I/P

+
1

-48V I/P

SK11

32Z

28Z

24Z

20Z

16Z

12Z

500mA SLOW

SK11

30D

26D

22D

18D

14D

10D

240VAC
I/P

1 15/07/97

CONTRACT No.

ENG. APP.

CHECKED

DRAWN

ALARM

+
1

-48V I/P

SK12

DRAWING No.

TITLE

SK12

30D

26D

22D

18D

14D

10D

803980

FRAME

FRU-2300

IRT Electronics Pty. Ltd.
ARTARMON NSW AUSTRALIA 2064

SCALE

SIZE

32Z

28Z

24Z

20Z

16Z

12Z

500mA SLOW

SHEET
1 OF 1

PCB 804040

P1-30D
ALARM

P1-32Z
GROUND

-48V

P1-18D

FUSE

RL1

.51

ZD1
BZT03-C68

C1
0.1

L1
RFC

1N4004

1N4004
2

RFC

C2
10n

C3
10u
1

VI-2NL-EW-F4

- IN

GATE OUT

GATE IN

+ IN

- OUT

_ SENSE

TRIM

+ SENSE

+ OUT

81M5

500K

RV2

C8
10n

C7
10n

RFC

C9
10n

CONTRACT No.

ENG. APP.

CHECKED

DRAWN

RBB

P1-22D
28V
RETURN

P1-24Z
COMMON

P1-20Z
+28V

PSU-2300

RL1
21ND12

R5
470

LD1

804039

DC-DC CONVERTER
DRAWING No.

TITLE

1
2
IRT Electronics Pty. Ltd.
ARTARMON NSW AUSTRALIA 2064

SCALE

SIZE

R4
270

ZD2
C11

2
1

D2
1

2 28/02/97
3 27/03/97

SHEET
1 OF 1

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