Versitron Fiber Optic Modem Manuals Resource

F271X

FOM II Series

Tele-Data

Fiber Optic Modem

Technical Manual



See Technical Data Sheet

See Application Diagram

Download Manual PDF

www.versitron.com

Revision B

Copyright May 2000

VERSITRON, Inc.

83 Albe Drive / Suite C

Newark, DE 19702


PROPRIETARY DATA

All data in this manual is proprietary and may not be disclosed,

used or duplicated, for procurement or manufacturing purposes,

without prior written permission by VERSITRON.

All VERSITRON products purchased after January 2001 carry a limited lifetime warranty against defects in material and workmanship. Purchases made prior to January 2001 are warranted for a period of one year from date of delivery. VERSITRON reserves the right to repair or, at our option, replace parts which during normal usage prove to be defective during the warranty period provide that:

1. You call VERSITRON at 302-894-0699 or 800-537-2296 and obtain a Return Maintenance Authorization (RMA) number. Please reference your RMA number on the outside of the shipment box.

2. Shipping charges are pre-paid.

No other warranty is expressed or implied and we are not liable for consequential damages. For repairs outside of the warranty period, the same procedure must be followed.

TABLE OF CONTENTS

 

SECTION 1: DESCRIPTION OF EQUIPMENT

1.1 INTRODUCTION

1.2 DESCRIPTION OF EQUIPMENT

1.2.1 Functional Characteristics

1.2.2 Audio and Data Transmission Characteristics

1.2.3 Physical Characteristics

1.3 TELE-DATA MODEM SPECIFICATIONS

SECTION 2: INSTALLATION

2.1 GENERAL

2.2 SITE SELECTION AND MOUNTING

2.3 SWITCH AND JUMPER SETTINGS

2.3.1 RS-485 / RS-422 Data Transmission Settings

2.3.2 Fiber Optic or Copper Transceiver Network Settings

2.3.3 Interface Impedance Selection

2.3.4 Ring Down Circuit Selection

2.3.5 Default Jumper

2.4 POWER REQUIREMENTS

2.4.1 Installation with AC Power

2.4.2 Installation with DC Power

2.5 INTERFACE WIRING

2.5.1 Fiber Optic Cable Installation

2.6 INITIAL CHECKOUT PRODEDURE

SECTION 3: OPERATION

3.1 INTRODUCTION

3.2 STATUS INDICATORS / AUDIBLE ALARM

SECTION 4: THEORY OF OPERATION

4.1 INTRODUCTION

4.2 POWER SUPPLY AND ALARM CIRCUITRY

4.2.1 Power Supply Circuit

4.2.2 Alarm Circuit

4.3 FUNCTIONAL DESCRIPTION

4.3.1 Ring Detection

4.3.2 Ring Down Circuit

4.3.3 Off-Hook Detection Circuit

4.3.4 Analog-to-Digital Conversion

4.3.5 CPLD (Mux / Demux)

4.3.6 RS-485 / RS-422 Data Transmission Circuit

4.3.7 Fiber Optic / Copper Transceiver Circuit

SECTION 5: MAINTENANCE AND TROUBLESHOOTING

5.1 INTRODUCTION

5.2 FAULT ISOLATION

LIST OF ILLUSTRATIONS

1.1 FONT VIEW, F271X MODEM

1.2 REAR VIEW, F271X MODEM

1.3 BACK PANEL, F271X MODEM

1.4 APPLICATION EXAMPLE

1.5 SWITCH AND JUMPER SETTINGS

1.6 DC POWER SUPPLY CONNECTIONS

List of TABLES

1 DIMENSIONS OF ENCLOSURES AND CHASSIS

2 SW1 SWITCH SETTINGS

3 JP4 JUMPER SETTINGS

4 SW2 SWITCH SETTINGS

5 LINE IMPEDANCE JUMPER SETTINGS

6 RING DOWN SETTINGS

7 DEFAULT SETTINGS

8 (J4) TELEPHONE/ANALOG WIRING

9 (P1) CHASSIS POWER/ALARM WIRING

10 (J1) RS-485/RS-422 DATA TRANSMISSION WIRING

11COPPER INTERFACE WIRING

12 STATUS INDICATORS

13 NONOPERATIONAL INDICATORS



SECTION 1

DESCRIPTION OF EQUIPMENT

 

1.1       INTRODUCTION

This manual provides general and detailed information on the installation and operation of the Model F271X FOM II Series Fiber-Optic Tele/Data Modems. Section 1 provides a general description of the equipment. Section 2 provides installation instructions. Section 3 provides operating instructions. Section 4 provides the theory of operation. Section 5 provides maintenance and troubleshooting information. Figures 1.1 and 1.2 provide an overall view of the Model F271X Tele/Data Modems.

Model
Number

Part Number

Description

F2712

19686-02

Audio, RJ11 and/or Data, RJ45 transmission, multimode, 850nm optics,   ST connectors, 2 Km operational

F2714

19686-04

Audio, RJ11 and/or Data, RJ45 transmission, multimode, 1300nm optics, ST connectors, 8 Km operational

F2715

19686-05

Audio, RJ11 and/or Data, RJ45 transmission, single mode, 1300nm optics, ST connectors, 14 Km operational

1.2       DESCRIPTION OF EQUIPMENT

 

1.2.1                            Functional Characteristics

The Model F271X products are fiber-optic Modems used as an interface extender from a single-line subscriber telephone.  These units are designed to be used with Model F270X Modems that provide an interface to the exchange or central office, or a pair of F271X can be used in a ring down or intercom application (see figure 1.4 for details).  These Modems are designed to transmit audio (Telephone) and/or data (RS-485 or RS-422) together on duplex fiber-optic cable or 4-wire twisted pair cable (depending on the application).  The main characteristics of Model F271X Modems are:

  • Multiplexes data (RS-485 or RS-422) and analog (Telephone audio signal), if desired
  • Transmits multiplexed data/audio signal on fiber-optic or copper interface cables
  • Offers ring down or intercom applications when using a pair of F271X subscriber Modems

 

Model F270X and F271X Modem pairs use multimode fiber-optic cable of up to 2 Km (6,560 ft/1.2 mi) for 850nm LED optics, up to 8 Km (26,240 ft/5 mi) for 1300nm LED optics, or single mode fiber-optic cable of up to 14 Km (46,200 ft/8.7 mi) for 1300nm ELED optics.  If a copper interface is used then up to  303 m(1000 ft/.189 mi) 4-wire twisted pair cable may be used to complete the circuit between the exchange (F270X) and subscriber (F271X) side Modems, or a pair of subscriber (F271X) Modems. 

1.2.2    Audio and Data Transmission Characteristics

The F271X series operates by accepting the audio signal at the RJ11 connector from the subscriber telephone and digitizing it, using an A/D converter.  This signal is then multiplexed with data (RS-485 or  RS-422) signals coming from the RJ45.  The combined signal is applied to a light pulse and transmitted over fiber-optic or 4-wire twisted pair copper cable to the remote F270X or F271X series unit.

The remote F270X or F271X series unit converts the light pulse (in cases of fiber-optic network connection) back into an electrical signal, demultiplexes the combined data/audio signal and applies the digitized signal to an A/D converter to recover the audio signal.  The separated data and audio signals are then sent to their respective destinations.  The outgoing signal path (exchange-to-subscriber or subscriber-to-subscriber) is similar.  The audio signal is digitized and multiplexed together along with the data (RS-485 or RS-422) signals and transmitted to the F271X series unit.  Finally, the F271X Modem recovers the audio and data signals.

The Model F270X/F271X transmits analog signals of 300 to 3400Hz and full duplex asynchronous / isochronous RS-485 or RS-422 data signals up to 64Kbps and is transparent in both directions.

1.2.3    Physical Characteristics

Model F270X/F271X FOM II Series Tele/Data Modems measure 7.0" wide x 0.84" high x 11.6" deep (17.8 x 2.1 x 28.9 cm) and are designed to be mounted in a variety of VERSITRON enclosures and chassis (see Table 1 for dimensions of enclosures and chassis).  "Desktop" options include both single- and dual-card enclosures.  Rack-mount options include a 2-card and 20-card 19” standard rack-mountable chassis.  For either desktop enclosure or 2-card rack-mount chassis, each F270X/F271X unit requires a wall transformer, VERSITRON Model PSAC08 (US) or PSAC09 (European), providing 12 VDC, 1A.  The one-pin power connector for electrical input is on the back of the card.  There are two RJ11 jacks for the telephone and copper interface (used in applications where there is no fiber-optic cable), a RJ45 jack for EIA RS-485 or RS-422 data connection and two ST connectors for the fiber-optic interface, also on the back of the card as shown in Figure 1.3.  For HF20 chassis installations, power is provided by VERSITRON Model AC150W Power Supply / System Monitor.  One AC150W utilizes two slots in the HF20.  Two AC150W units are recommended for power redundancy.  Both F270X and F271X models have six indicator LEDs: power (PWR), off-hook (HOOK), ring signal (RING), loop detection (LOOP), reverse battery signal (RBAT), and alarm (ALM).  No audible alarm is available.

Model
Number

Part
Number

Dimensions
(H x W x D)

Description

Power Supply Required

HF1

19052

1.3" x 7.1" x 11.6"

Single Card Desktop Enclosure

PSAC08 (115 VAC) or PSAC09 (230 VAC)

HF2

19053

2.3" x 7.1" x 11.6"

Dual Card Desktop Enclosure

PSAC08 (115 VAC) or PSAC09 (230 VAC)

HF2SS

19629

1.7" x 19.0" x 13.8"

Dual Card Rack Mount Chassis

PSAC08 (115 VAC) or PSAC09 (230 VAC)

HF20

19032

7.0" x 19.0" x 11.6"

20-Card Rack Mount Chassis

AC150W (115 or 230 VAC)

*¹ Note:  One Power Adapter per  Modem required.

TABLE #1  DIMENSIONS OF ENCLOSURES AND CHASSIS 

 

Front view F271X Modem

FIGURE 1.1  FRONT VIEW, F271X MODEM

 

 

Rear View F271X Modem

             FIGURE 1.2  REAR VIEW, F271X MODEM

 

 

Back Panel 271X

FIGURE 1.3  BACK PANEL, F271X MODEM

Application Example 

FIGURE 1.4  APPLICATION EXAMPLE

 

1.3 Tele/Data Modem Specifications

General Specifications

Models

F270X /F271X*¹

Dimensions

(7" H x 7/8" W x  11" L)  (17.8 x 2.1 x 27.9 cm)

Weight

0.34 kg (12 oz)

Operating Temperature

0° to 50°C (32° to 100°F)

Humidity

Up to 95% relative humidity (noncondensing)

Altitude

Up to 10,000 ft


Note: *¹ X is replaced with 2, 4, or 5  for 850nm MM, 1300nm MM, or 1300nm SM, respectively.

Electrical Interface

Models

F270X /F271X*¹

Power Requirements

12VDC, 1Amp

Connector (Tip & Ring)

RJ11, 2-Wire Twisted Pair

Copper Interface Connector

RJ11, 4-Wire Twisted Pair

Data Transmission Connector

RJ45, CAT 5 UTP

Audio Signal

Analog, 300 to 3400Hz

Data Signal

RS-485 or RS-422 asynchronous or isochronous

Data Rate

Up to 64Kbps

Idle Channel Noise

-55dBm

In-Band Spurious

-40dBm

Out-Band Spurious

-30dBm

Talk Battery

45 to 55 VDC

Loop Current

20mA max (off hook)

Ring Signal

80-150VAC, 15 to 68Hz

Line Impedance (Jumper selectable)

60 Ω or 900 Ω


Note: *¹ X is replaced with 2, 4, or 5  for 850nm MM, 1300nm MM, or 1300nm SM, respectively.

Fiber Optic Interface

Models

F2702/F2712

F2704/F2714

F2705/F2715

Wavelength

Multimode 850nm

Multimode 1300nm

Single Mode 1300nm

Connector

ST

ST

ST

Transmit Output Power
-10 ± 1 dBm

-12 ± 1 dBm

-20 ± 1 dBm

Receiver Sensitivity

-30 ± 1 dBm

-32 ± 1 dBm

-34 ± 1 dBm

Maximum Range

Up to 2 Km

Up to 8 Km

Up to 14 Km

Fiber-optic Cable Size

50/125, 62.5/125, 100/140

50/125, 62.5/125,100/140

8/125, 9/125,10/125

Major Features

  • Intercom or Ring Down Application with two Subscribers, F271X
  • Copper-to-Copper Option (Applications which don’t require fiber, maximum distance up to 1000 feet)
  • Copper-to-Fiber Network Application Option
  • 850nm Multimode, 1300nm Multimode and 1300nm Single Mode Options
  • Data and Audio Multiplexing
  • Line Impedance Option of  600 Ω or 900 Ω

 

SECTION 2

INSTALLATION

2.1 GENERAL

This section contains detailed information on the installation and initial checkout of the Model F271X FOM II Series Modems.  Paragraph 2.2 contains general information on site selection and rack mounting. Paragraph 2.3 contains the description for selecting different options on the Modem.  Paragraph 2.4 and 2.5 contain detailed instructions for connecting Model F271X products to your system.  Paragraph 2.6 contain initial checkout procedures.

2.2       SITE SELECTION AND MOUNTING

The Model F271X FOM II products are designed as a single line Modem, providing one telephone interface.  This particular series can also be connected directly to the serial port (RS-485 or RS-422) of the terminal or data communication equipment with a CAT-5 UTP cable (customer supplied).  When attaching the F271X Modem to a PC, Fax, or STU III, the copper and fiber-optic cable should be securely installed so as to prevent accidental disconnection.  Care should be taken to ensure that the copper and fiber-optic cables are not mechanically separated from the Modem during operation. Space for the power transformer must also be provided.

2.3 SWITCH AND JUMPER SETTINGS

Internal switches and jumpers are provided to select between available options on the F271X. Switch and jumper locations are shown in figure 1.5.  Switch and jumper settings are as follows:

2.3.1 RS-485 / RS-422 Data Transmission Settings

The F271X Modem has an option of changing the polarity of the transmit or receive data signals at the RJ45 jack.  This eliminates a need to reterminate the UTP cable and change the wiring in a RJ45 plug.

Positions

On

Off

SW1-1

Factory setting*

Factory setting*

SW1-2

Inverts the phase/polarity for the RS-485/RS-422  receiver inputs

Normal phase/polarity for the
RS-485/RS-422 receiver inputs

SW1-3

Inverts the phase/polarity for the RS-485/RS-422 transmitter outputs

Normal the phase/polarity for the
RS-485/RS-422 transmitter outputs

SW1-4

Subscriber-to-subscriber, Ring down or intercom application

Subscriber-to-exchange, Normal operation

* Note:  Factory setting for SW1-1 is Off.

* Note:  Do not set SW1-1 in the On position.

TABLE 2: SW1 SWITCH SETTINGS

 

2.3.1    RS-485 / RS-422  Data Transmission Settings (cont’d)

Jumped*

Functional Description

JP4 2 & 3 Slew rate set to 10Mbps

* Note: Factory setting. Do not change.

TABLE 3:  JP4 JUMPER SETTINGS

2.3.2 Fiber Optic or Copper Transceiver Network Settings

A new feature to the VERSITRON class of Modems is the ability of the F270X and F271X Series Modems to multiplex data (RS-485 or RS-422) and analog (Telephone audio signal) onto a fiber OR copper network, depending on the application.  Figure 1.4 shows an example for a copper and fiber network circuit.  The selection for a copper (4-wire twisted pair) or a fiber optic interface is accomplished by the following dip switch settings:

Position

Copper Interface

Fiber Interface

SW2-1

On

Off

SW2-2

Off

On

SW2-3

On

Off

SW2-4

Off

On

TABLE 4:  SW2 SWITCH SETTINGS

 

2.3.3    Interface Impedance Selection

The telephone/analog frequencies look into impedance known as the line impedance.  In the USA and North America it is about 600Ω. In Europe and the Far East it is usually 900Ω. F270X and F271X comply with both standards, depending on the jumper settings.  These settings are as follow:

Jumper

Jumped*

Functional Description

JP2

1 & 2

900 Ω line impedance

JP2

2 & 3

600 Ω line impedance

JP3

Jumper off / removed

900 Ω line impedance

JP3

Jumper on / in

600 Ω line impedance

*Note: Factory Setting: JP1: (2 & 3 are jumped) and JP2: (Jumper on / in)

TABLE 5: LINE IMPEDANCE JUMPER SETTINGS

2.3.4 Ring Down Circuit Selection

The new subscriber Modem, F271X, has been upgraded to include a ring down circuit.  This circuit  allows two subscribers to be connected together in pair.  The following settings need to be made before connecting a pair of F271X:

Jumper/Switch

Normal Settings

Ring Down Settings

JP7

Jump 2 & 3

Jump 1 & 2

JP8

Jump 1 & 2

Jump 2 & 3

SW1-4

Off

On

Note:  Refer to figure 1.5 for the locations of JP7, JP7 and SW1-4

TABLE 6:  RING DOWN SETTINGS

In a ring down configuration, whenever a telephone attached to one of the F271X Modems goes off-hook, the F271X Modem on the other end starts ringing the telephone attached to it. When the receiver is picked up, the ringing stops and a conversation is possible.  Application examples for this type of setup would be for 911 emergency or intercom. (Note: If a F271X Modem is set up in a ring down or intercom application, it will not operate with a F270X exchange side Modem.) 

Jumpers

Factory Settings

Important Instruction

JP11

Jump 2 & 3

Do not change

JP12

Jump 2 & 3

Do not change

Note:  Refer to figure 1.5 for the locations of  JP11 and JP12

TABLE 7:  DEFAULT SETTINGS

Switch and Jumper Settings

FIGURE 1.5 SWITCH AND JUMPER SETTINGS

 

2.4 POWER REQUIREMENTS

The Model F270X FOM II products are designed to operate from an AC power transformer or a DC power source in the range of +12 to +18 VDC.

2.4.1 Installation with AC Power

Before inserting the VERSITRON power transformer, PSAC08 (US) or PSAC09 (EUR), into an AC power source, the plug should be connected to the Modem.  There are no special tools required.

2.4.2 Installation with DC Power

DC power may be used instead of a power transformer.  This requires a 2.5 mm socket, J3 (location shown in figure 1.5) with the positive voltage on the center and the common on the concentric supplying 12VDC at 1A as shown below:

DC Power Supply Connections

FIGURE 1.6  DC POWER SUPPLY CONNECTIONS

 

2.5 INTERFACE WIRING

Tables 8, 9, 10 and 11 list the interface wiring for Model F271X FOM II Series Modems. The RJ11 (J4) is used with a single line 2-wire telephone.  Wiring for (J4) is shown in Table 8.  The modular connector (J3) is wired in parallel with the 12-pin connector (P1) for power.  When installing the telephone Modem as a standalone unit, a power transformer modular jack (J3).  When installing the telephone Modem in a 20-card rack-mount chassis (Model HF20) with optional power supplies (AC150W) the 12 pin connector (P1) is used.  Wiring for the 12-pin connector is shown in Table 9.  RJ45 (J5) is used for RS-485/RS-422 data transmission.  Wiring for J5 is shown in Table 10.  RJ11 (J6) is used in applications where data/audio or both are meant to transmit on a copper, instead of fiber-optic network.  Settings for the copper interface are previously explained in section 2.3.2.  Wiring for the copper interface is shown in Table 11.  Figure 1.5 identifies the locations for RJ11 jack (J4), 12-pin power connector (P1), modular power jack (J3), RJ45 (J5) and RJ11 (J6) jacks. 

Pin Number

Signal Designation

Color

1

Not Used

-

2

Not Used

-

3

Ring

Green

4

Tip

Red

5

Not Used

-

6

Not Used

-

TABLE 8:  (J4) TELEPHONE / ANALOG WIRING

 

Pin Number

Signal Designation

1

+12 VDC

2

+12 VDC

3

Signal Ground

4

Signal Ground

5

Signal Ground

6

Frame Ground (Chassis)

7

System Alarm Interface

8

Signal Ground

9

Signal Ground

10

+12 VDC

11

+12 VDC

12

+12 VDC

TABLE 9:  (P1) CHASSIS POWER / ALARM WIRING

Interface

SW1-2

SW1-3

Pin Number

Signal Designation

Color

Normal Phase/Polarity

Off

Off

1

RX+

Orange w/ White Line

2

RX-

Orange

3

TX-

Green w/ White Line

6

TX+

Green

Inverted Phase/Polarity

On

On

1

RX-

Orange w/ White Line

2

RX+

Orange

3

TX+

Green w/ White Line

6

TX-

Green

TABLE 10:  (J5) RS-485 / RS-422 DATA TRANSMISSION WIRING

Pin Number

Signal Designation

Color

1

Not Used

-

2

RX-

Yellow

3

RX+

Green

4

TX+

Red

5

TX-

Black

6

Not Used

-

TABLE 11:  (J6) COPPER INTERFACE WIRING

 

2.5.1 Fiber Optic Cable Installation

After the electrical and digital interface cables have been wired according to paragraphs 2.4 and 2.5, the fiber-optic cable may be attached to the F271X.  The transmitter module of each unit should be connected to the receiver module of the other unit. That is, the transmitter optic of the exchange side Modem, F270X, should be connected to the receiver optic of the subscriber side Modem, F271X.  On the other hand, the transmitter of the subscriber side Modem, F271X, should be connected to the receiver optic of the exchange side Modem, F270X.  Similarly, when a pair of subscriber Modems, F271X, are used in a ring down application, the same kind of fiber-optic connections are required.

 

2.6 INITIAL CHECKOUT PROCEDURE

The Model F271X FOM II Series Modems contain no power on/off switch.  Once the unit is properly installed and power is applied it should be fully operational.  The power indicator should remain on as long as power is supplied to the unit. Before beginning system operation the following items should be checked to verify proper installation:

  1. Verify that the power plug is seated fully into the Modem or seated firmly in the rack-mount chassis.
  2. Verify that the fiber cable is crossed transmit to receive from unit one to two and unit two to one.
  3. Verify that the alarm LED goes out when the signal is applied to the optical receiver of the F271X, or when 4-wire UTP is connected between F270X and F271X in a copper network application.
  4. Verify the switch settings for the circuit configuration. (i.e. copper or fiber-optic network interface).

If a malfunction is detected during the initial checkout procedure, refer to Section 5 for information on isolating the malfunction in the unit.


SECTION 3

OPERATION

 

3.1 INTRODUCTION

This chapter contains a description of the operating controls and indicators associated with the Model F271X FOM II Series Modems.  Since the Model F271X is designed for continuous and uninterrupted operation, there are no setting requirements after the unit is operational.  Once the Modem is powered up it should remain in service as long as required.

3.2 STATUS INDICATORS / AUDIBLE ALARM

There are 6 indicators on the Model F271X: power (PWR), off-Hook (HOOK), ring detect (RING), loop detect (LOOP), reverse battery (RBAT), alarm (ALM).  No audible alarm is available.

 

LEDs

Color

Function

PWR

Green

Indicates operating voltage is present at the power interface connector

HOOK

Red

Indicates that the telephone set has gone OFF-HOOK, when lit

RING

Red

Indicates RING signal coming from the exchange side Modem, F270X or from the subscriber side Modem F271X, in a ring down application, when lit or blinking

LOOP

Red

Indicates the successful loop closure on the exchange side Modem upon receiving an OFF-HOOK signal from the subscriber side Modem, when lit

RBAT

Red

Indicates Reverse Battery condition of the exchange side Modem F270X, when lit

ALM

Red

Indicates the following when lit:

  • +5V power supply circuit is not working
  • –5V charge pump circuit is not working
  • +12V Power supply is not working
  • A problem exists with data transmission

TABLE 12:  STATUS INDICATORS


SECTION 4

THEORY OF OPERATION

4.1 INTRODUCTION

The F271X is a subscriber side Tele/Data Modem with ST single or multimode fiber-optic connectors.  These Modems are designed to work with F270X subscriber side Modems in pair and interface with audio and RS-485/RS-422 data grade signals.  These units can also work in pairs when used in ring down or intercom applications.  These units are housed in VERSITRON FOM-II chassis: HF1, HF2, HF2SS and HF20.  Chassis descriptions are in paragraph 1.2.3.

4.2 POWER SUPPLY AND ALARM CIRCUITRY

4.2.1 Power Supply Circuit

When 12VDC is applied to the circuit, the unit should draw between 100mA and 130mA depending on the Modem state.  The unit has a switching power supply circuit, which converts 12V to 5VDC and a charge pump circuit, which converts 5V to -5VDC.  The switching power supply has a switching frequency of 44.4Khz determined by a single capacitor C49 (1800pF) and an under voltage lockout feature.  This feature is produced by CR5 (1N755) and CR6 (1N4148).  The under voltage lockout is accomplished as follows:

When the input voltage becomes lower than the zener breakdown voltage, the output transistor is turned off.  This occurs because diode CR6 at that time becomes forward bias, allowing resistor R43 to sink a greater current from the non-inverting input than is sunk by the parallel combination of R44 and R45 at the inverting terminal.

4.2.2 Alarm Circuit

Alarm LED goes off when one of the following occurs:
 

  • +5V power supply circuit is not working
  • –5V charge pump circuit is not working
  • +12V power supply is not working
  • A problem exists with data transmission and a mux clock is not present at U5 (HC123)

These conditions activate the base of Q3, which activates the base of Q2 and starts current flowing through DS6, the alarm LED.  When Q2 is activated this also changes the voltage level of connector P1 pin 7 that activates the system alarm circuit on the power supply.

4.3 FUNCTIONAL DESCRIPTION

The unit consists of the following circuits:

4.3.1 Ring detection
4.3.2 Ring down circuit
4.3.3 Off-Hook detection circuit
4.3.4 Analog to digital conversion
4.3.5 CPLD (Mux/Demux)
4.3.6 RS-485/RS-422 data transmission circuit
4.3.7 Fiber-Optic/Copper transceiver circuit

4.3.1 Ring Detection

The optical receiver detects the ring signal coming from the exchange side Modem F270X.  Then it is fed to the CPLD, which separates the signal from rest of the multiplexed data and sends it to the subscriber’s telephone set.  The ring voltage at the subscriber side Modem, F271X is about 100VAC @ 20Hz ± 3Hz.

4.3.2 Loop Current Detection Circuit

The ring down circuit is used when two F271X, subscriber Modems are connected together.  F271X Modems have a 556 Timer IC, which basically produces a 20Hz ± 3Hz clock pulse.  This clock pulse is then used to ring the telephone attached to the Modem.  Settings for ring down circuit are explained in paragraph 2.3.4.

4.3.3 Reverse Battery Detection Circuit

When the telephone set that is attached to the Modem goes Off-Hook, current flows through the Tip and Ring of the circuit.  U14 optocoupler detects the current and triggers a signal indicating Off-Hook condition.  The ring battery of -48VDC with respect to the Tip is provided by the Modem, which is the source of the current.  The current may vary from 17mA to 25mA.

4.3.4 Analog-to-Digital Conversion

A 2W/4W Hybrid circuit is used before the A/D circuit, this signal is then digitized and band limited for the digital system.  On the reverse path the digital data stream is reconstructed into an analog audio signal.  The sampling rate on the audio signal is 256Khz to ensure signal quality.

4.3.5 CPLD (Mux / Demux)

The CPLD is used to perform the mux/demux of the digitized audio and RS-485/RS-422 digital data signal.  In essence, it is an asynchronous-to-synchronous converter encoded using proprietary VHDL programing designed at VERSITRON.  A 20MHz Oscillator, Y1, provides the clock input to the CPLD.

4.3.6 RS-485 / RS-422 Data Transmission Circuit

In the data transmission circuit, a RS-485/RS-422 interface IC, U17, is used. This IC takes in a balanced data signal and converts it into a TTL signal.  Then the TTL data signal is fed to the CPLD, where it is multiplexed with the digitized audio signal.  During the data reception, the TTL signal is obtained from the CPLD, which then enters the interface IC.  Here the data is reformatted to a RS-485 or RS-422 signal and is transmitted out of the RJ45 connector.

4.3.7 Fiber Optic/Copper Transceiver Circuit

This design has an option of multiplexing data (RS-485 or RS-422) and analog (Telephone audio signal) onto either a fiber or copper network.  The selection for copper (4-wire twisted pair) or fiber interface is accomplished by dip switch settings as described in paragraph 2.3.2.

When the multiplexed audio and data signals are transmitted out of the CPLD, it goes into the JFET, Q1 (VN10KM).  By turning on and off Q1 JFET VN10KM, the fiber-optic transmitter Z2 is turned on and off respectively.  This is how the optical signal is transmitted out of the Modem.  On the receive side,  optical receiver Z1 takes the optical signal from the fiber and converts it into a low voltage current.  This current signal is fed into the fiber-optic quantizer IC, through 0.01mF coupling capacitor, C63.  This chip converts the low voltage signal into a TTL signal, which then goes into the CPLD where the multiplexed audio and data signals are de-multiplexed and sent to their respective destinations.

When a copper-to-copper interface is selected, the multiplexed audio and data signal is transmitted out of the CPLD, which then goes into U22, a full duplex RS-485/RS-422 interface IC.  This chip converts the TTL data signal into a RS-485/RS-422 signal, which is transmitted on a 4-wire twisted pair telephone wire.  On the reception side, U22 a full duplex RS-485/RS-422 interface IC receives the signal from a 4-wire UTP wire.  The RS-485/RS-422 data signal is converted into a TTL data signal and transmitted to the CPLD, U3.  Here the multiplexed audio and data signals are de-multiplexed and sent to their respective destinations.


SECTION 5

MAINTENANCE AND TROUBLESHOOTING

5.1 INTRODUCTION

This chapter contains general information designed to isolate a malfunction in the Model F270X to a replaceable unit.  These units are not equipped with redundancy.  Therefore, a failure in one of these units would interrupt service.

5.2 FAULT ISOLATION

The steps in Table 13 should be taken to check a nonoperating Modem.  Contact VERSITRON Customer Service for additional diagnostic assistance or to arrange for repair as necessary.

STATUS INDICATOR

PROBABLE CAUSE

CORRECTIVE ACTION

POWER (PWR) LED is OFF

No AC power

Check that both ends of the transformer are connected

Blown Fuse

Replace with 250V 1A slo-blo fuse

Other power supply circuit problem

Contact VERSITRON for assistance

ALARM (ALM) LED is ON

Incorrect optical signal level received at receiver input

  1. Check that fiber optic cables are properly connected
  2. Check that the remote unit power is on and the fiber optic connectors are properly attached
  3. Measure the optical levels on both ends (if possible) in order to check the optical link
  4. Contact VERSITRON for assistance

HOOK LED is ON

Possible problems ranging from a telephone set in an Off-Hook position to a problem with the Off-Hook circuit

Check if the telephone set receiver is seated in cradle correctly. If this is not the case, contact VERSITRON for assistance 

LOOP LED is ON

The current supplied by the central office is fluctuating from 17mA to 25mA

Check the exchange side Modem on the other end and check the exchange line coming from the central office or the Switch

RBAT LED is ON

Voltage between Tip and Ring are reversed

Check that the Tip and Ring on the 2-wire UTP coming from the central office are not reversed. That is, Tip wire is not connected to the Ring on the Modem’s RJ11 connector and vise versa

Modem is not working in a subscriber, F271X to exchange, F270X application

Jumpers and switch settings are not set for this application

  1. Check if SW1-1 is OFF
  2. Check if SW2 is properly set for the desired interface (i.e. copper or fiber network application, see table 4)
  3. Check if SW1-4 is in Off position
  4. Check if JP7 is jumped between pin-2 and 3
  5. Check if JP8 is jumped between pin-1 and 2
  6. Contact VERSITRON for assistance
Modem is not working in a subscriber, F271X to subscriber, F271X ring down application Jumpers and switch settings are not set for this application
  1. Check if SW1-1 is OFF
  2. Check if SW2 is properly set for the desired interface (i.e. copper or fiber network application, see table 4)
  3. Check if SW1-4 is in On position
  4. Check if JP7 is jumped between pin-1 and 2
  5. Check if JP8 is jumped between pin-2 and 3
  6. Check if JP11 and JP12 have jumpers between pins 2 and 3
  7. Contact VERSITRON for assistance
TABLE 13:  NONOPERATIONAL INDICATORS

 

If you are still experiencing problems, please contact VERSITRON customer service for assistance at 302-894-0699 or 800-537-2296.

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