Installation
and Testing
5 Mbit/s
Repeater
Carrier-band
to Single-mode
Fiber Optic
Models
CBR-7AC
CBR-7DC
This manual describes the procedures for installing and testing the CBR-7 Fiber-Optic Repeaters.
o For an explanation of how to install the coaxial cable part of the carrierband net wor k, see
Relcom’s Carrier-band Network Handbook.
o For an explanation of how fiber optics works, see Relcom’s Gu ide to Indust r ial Fiber Optics.
o For an explanation about how repeaters work, and CBR-7 s yst em design information, see
Relcom’s CBR-7 System Desig n Application Note, document 501-276.
o For technical specifications, see the CBR-7 produ ct specification, document PS-02 9.
CBR-7 Installation and Testing 501-281, Rev C.0
1
Repeater Installation
The Repeater is connected to segments o f the Carrier-band network like any other station
through a drop cable and a tap. The following should be considered when installing a Repeater:
o Place the Repeater where its indicat or lights can be seen. This will help ident ify and iso lat e
network problems if they occur.
o While the Repeater is fully enclosed, it is not wat erproo f. Install the Repeater in a dry place.
o The Repeater operates at temperatur es between -20 and +65 °C (-4 to 150 °F). However, do
not install the Repeater in places where it will be heated by other equipment or where t here is
no airflow.
o A rack mounting kit for the Repeater is available.
Power
The Repeater is powered from an AC or DC power source depending on the option chosen.
CBR-7AC power input range is from 85 to 240 volts, 47 to 63 Hertz. The power cord connection
to the Repeater is a standard IEC 320 plug. Different types of power cords can be used to adapt
to various types of power sources.
CBR-7DC power input range is fro m 18 to 36 Vo lts DC.
CBR-7DC:
WARNING: FOR PERMANENTLY CONNECTED EQUIPMENT, A READILY
ACCESSIBLE DISCONNECT DEVICE SHALL BE INCORPORATED IN THE FIXED
WIRING.
AVERTISSEMENT: POUR LES ÉQUIPEMENTS RACCORDÉ S E N PERMANENCE , UN
DISPOSITIF DE DÉCONNE XION FACILEMENT ACCESSI BLE DOIT ÊTRE INCORPORÉ
DANS LE CÂBLAGE FIXE.
Grounding
Both F-connectors are grounded to the Repeat er 's case for r educing RFI emissio ns.
The Repeater's case is connect ed to the front panel TEST F-co nnector, to the mains ground
connection on the AC model, to the GND terminal on the DC model, and to the ¼-20 stud on the
back panel.
Attach a ground wire from the ground stud to the grounding facilities provided in the building.
Use a grounding wire that has a current carrying capacity equal or greater than that of the drop
cable outer conductor.
CBR-7 Installation and Testing 501-281, Rev C.0
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Hazard ous Area Warning
For both AC and DC Repeaters, users are war ned not to disconnect power to t he Repeat er
while the circuit is alive unless the location is known to be non-hazardous.
AC Power plugs
CBR-7 Installation and Testing 501-281, Rev C.0
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Testing
A self-testing capability is provided for checking t he o per ation of the Repeater before it is
connected to a network or if a malfunction is suspected.
1. Connect the Repeater to a power source.
The power indicator light, PWR, should be ON. The other indicator lights should be OFF
2. Connect the short test cable from the TEST F-connector to the F-connecto r labeled A.
3. If another Fiber Optic Repeater is available, co nnect the XMIT line of the first Repeater to the
REC line on the second Repeater . T he ACTIVE light for the Fiber Opt ic input o n the second
Repeater should be ON.
4. Connect F-connecto r A of the second Repeater with a 75 ohm terminated cable to an
oscilloscope. The second Repeat er will put out signal bursts o n its connecto r A. The peak-topeak voltage of the bursts should be between 3.0 and 3.9 Volts. (Keep in mind that the cable
gives a direct reading and is not a 10:1 probe.)
Repeat the procedur e with the Repeaters reversed. T est o nly one direction at a time with a single
fiber optic cable connecting the two repeater s.
There is no built-in pr ovision for testing the Fiber Opt ic input or output other tha n to connect two
Repeaters back-to- back and use the TEST signal to check the oper ation of the Fiber Optic ports
as described above.
If these tests do not produce the specified results, the Repeater (s) may be defective and should be
returned for repair.
THERE ARE NO USER ADJUSTMENTS OR REPAIRS TO BE MADE INSIDE THE
REPEATER.
For guidance about installing the carrier-band segment of the netwo r k, see Re lco m's Carrierband N etwork Hand book.
CBR-7 Installation and Testing 501-281, Rev C.0
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Troubleshooting
During normal Repeater oper ation, t he PWR light is ON, t he t wo ACTIVE lights are ON and
OFF intermittently and the ERROR lights may blink occasionally. I f not, check the following list
of symptoms and possib le corrections:
1. The PWR light is OFF
Check the power cord and the power source.
2. An ACTIVE light is ON indicates that data is being received from that network segment.
Normally the ACTI V E light shows differing levels o f brightne s s indicating the relative amount
of data received from the corresponding segment. If the light is solidly OFF, no data is being
received. The causes may be:
The Repeater is disconnected from the network segment. Check the networ k wiring.
None of the stations on the network segment ar e transmitt ing.
The signal from the coaxial cable to t he Repeat er is too low. Check the signal level wit h the
Carrier-band Tester.
The Repeater is defective. Check the Repeat er with the t est pro cedur es above.
3. If the ERROR indicator light blinks ON the Repeater has rece ived a frame with an error. T he
ERROR light should blink ON no more than once every 20 seconds. This correspo nds to a bit
error rate of about 10 -8 or o ne bad b it receiv e d fo r one hundr ed million sent. If the ERRO R light
blinks ON more frequently:
There may be excessive noise on the network coaxial cable segment. Use the Carrier-band Tester
to determine the noise level.
The Repeater may be receiving a signal from the coaxial cable that is too low. This may be a
result of improper network design, failure in the cables or taps, or some station not transmitting
at a s u fficiently high signal level.
Note: Some systems are setup to switch between cables on a regular basis. These transitions may
also cause the ERROR indicator to blink; these ERROR indicat ions are part o f the normal
operation of the system and they can be ignored.
The Repeater detect s two types of errors:
a. If the Repeater detects a start delimiter of a frame but no end delimiter before the received
signal drops below threshold.
b. If the Repeater detects three consecutive "highs" or three consecutive "lows" within a bit cell.
These are violations of the data encoding used in carrier-band.
The Repeater does not check frame CRCs o r other types o f networ k erro r s. The ERROR
indicator lights are only a diagnost ic aid for pointing to a segment that may be generating more
than the expected number of erro r s.
THERE ARE NO USER ADJUSTMENTS OR REPAIRS T HAT CAN BE PE RFORMED ON
THE REPEATER. IF THE REPEATER DOES NOT WORK PROPERLY, RETURN IT TO
RELCOM FOR REP AIR OR RE P LACEMENT.
CBR-7 Installation and Testing 501-281, Rev C.0
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Fiber-Optic Testing
When the CBR-7 repeaters and the opt ical component s ar e installed, the y must be t est ed to ver ify
that they work properly.
The fiber opt ic components between t wo CBR- 7 repeaters must be able to carry light signals
from the transmitter of one repeat er to the receiver of the ot her. The components include the
main cable between the two repeaters, and may also include a patch panel at each end, the pat ch
cables, and an attenuator. Some insta llations may also have more optical interconnection
components.
Patch Panel
Patch Panel
The total attenuation (insertion loss) of optic a l components must be at le ast 15
dB but not more than 24 dB. If necessary, an attenuator must be used on the
transmit side of the main fiber-optic cable.
For example: Assume that each optical connect ion has an attenuat ion o f 0.5 dB and there are
two connections at the transmitter side and two at the receiver side. T he main cable is 8 km long
and has an attenuation of 0.4 dB/km for a total attenuation of 3.2 dB. The total fiber-optic
attenuation is
2 X 0.5 + 3.2 + 2 X 0.5 = 5.2 dB
To get into the needed attenuation range, a 10 dB attenuator needs to be put at the transmitter
output. Th e calculated attenuation of all the fiber optic components is:
10 + 5.2 = 15.2 dB.
CBR-7 Installation and Testing 501-281, Rev C.0
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Attenuation Measuremen t
Determine the light o ut put leve l o f the CBR-7 transmitter. Disconnect all patch cables fro m the
transmitter . Connect a co axial cable bet ween t he Test and the A connector s of the CBR-7.
Connect a light meter to the tr ansmit connector. Power the CBR-7 and measure the transmitter
light level.
XMIT
B
Rec
CBR-7
A
TEST
-5 dBm
Light
Meter
Disconnect the light meter from the transmitter. Connect the patch cable to the transmitter and
all the other optical components. Measure the light level at the receiver of the corresponding
CBR-7 repeat er. This should be close to the level measur ed at the transmitter minus t he
calculated attenuat ion determined at design.
Patch Panel
Patch
Cable
-11.2dBm
Light
Meter
CBR-7
XMIT
REC
TEST
Patch Panel
Patch
Cable
Attn
B
A
Cable
CBR-7 Installation and Testing 501-281, Rev C.0
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From the example above, if the light measured at the receiver is -11.2dBm then the Measured
Attenuation of the optical components is:
-5dBm (the measured transmitter output) – (-11.2dBm) = 6.2 dB
This is 1 dB more than the calculated attenuation value. A variation of 1 dB is not critical. A
larger deviation would indicate a problem with the attenuation estimate and might indicate that
optical component s are o ut of specification.
CBR-7 Installation and Testing 501-281, Rev C.0
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Return Loss
CBR-7 per for mance dep ends on low retu r n losses ( reflections) of the optical component s. This
must be measured to be sure all the optical components are w ithin their specifications.
Transmit side
With all the optical co mpone nt s connected together, disconnect the pat ch cable at t he CBR-7
transmitter and measure the return loss of the optical components without the attenuator with an
Optical Time Domain Reflectometer, OTDR, as shown below. Neglect any near-end readings.
The return loss of interest is that at the end of the cable as seen from the transmitter end. Note
the value as Transmit Retur n Loss.
CBR-7 Installation and Testing 501-281, Rev C.0
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Receiver side
With all the optical co mponents connected, d isconnect the CBR-7 at the receiver. ( Be sure that
the CBR-7 o n the transm it s ide is not powered). Measure the retur n loss o f the o ptical
components as shown below. Neglect any near-end readings. The retur n loss of interest is that
at the end of the cable as seen from the receiver end. Note this as Receive Return Loss.
For proper op er at ion of the CBR-7 repeaters over the fiber optic cable
The value of the attenuator + Transmitter Return Loss + Receiver Return
Loss must be at least 48 dB.
If this is not the case, there is something wrong with the attenuator or the patch cable assemblies
that produces extraordinary reflections.
In the example above, the att enuator’s value is 10 dB. Assume the measured Transmitter Return
Loss is 20.2 dB and the Receiver Return Loss is measured to be 32.2 dB. Then
10 Attenuator value
20.2 Transmit Return Loss
32.2 Receive Return Loss
62.4 Total
In this example, the total of 62.4 is over the required 48.
For both the Transmitter and Receiver ret ur n loss measure ment s, neg lect any near-end read ings.
The measurement of interest is at the end of the cable. If there are ot her reflections that are not at
the cable’s length mark and these are closer to the measure ment of interest t han 10 dB, then there
is something wrong with the optical components at that locat ion.
CBR-7 Installation and Testing 501-281, Rev C.0
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Here is an example:
The top of the screen is at -10 dB. There are two reflections. One is at 4 km and the other at 8
km, at the end of the cable. The one at 4 km is 15 dB below the one at the end and it can be
neglected since it is more than 10 dB below the reflection of interest at the end of the cable. The
reflection at the end of the cable is at -14 dB. The return loss at the end of the cable due to this
reflection is 14 dB, as seen from the other end of the cable where the measurement is made.
CBR-7 Installation and Testing 501-281, Rev C.0
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