METROTEC VNA-70A User manual

Voice Network Analyzer

MODEL VNA-70A

Instruction Manual

P/N 82-70-027

February 2004

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TABLE OF CONTENTS

1.0 INTRODUCTION

2.0 GENERAL DESCRIPTION

3.0 CONTROLS

4.0 OPERATION

4.1 BATTERY TEST

4.2 BRIDGING AND TERMINATING

4.3 VOICE NETWORK ANALYZER

4.3.1DC VOLTS

4.3.2DC MILLIAMPERES

4.3.3DBm

4.3.4AC VOLTS

4.3.5FREQUENCY

4.3.6TONE GENERATOR

4.3.7OHMS

4.4.DIGIT DISPLAY

4.4.1.OPERATION

4.4.2.DIAL PULSE LEVEL SELECT

4.5.MONITOR SPEAKER

5. POWER SOURCE

6. SPECIFICATIONS

7. APPLICATION NOTES

8. WARRANTY

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1.0 INTRODUCTION

This document provides information on the Model VNA-70A Voice

Network Analyzer Test Set. Included are descriptions of the instrument

controls, functions, specifications and applications. The information is

designed for test engineers and technicians.

2.0 GENERAL DESCRIPTION

The VNA70-A is a comprehensive telecom test instrument which

offers several modes of operation designed specifically for the telecom

environment. Model 70A is an enhanced version of the earlier Model 70

with the addition of Ohms test capability.

The test set acts as a DVOM, a frequency counter, oscillator, dialed

digit display and milliammeter. This unique set of functions are selected to

allow thorough troubleshooting of the local telephone loop and the premise

equipment connected to it.

The instrument is battery powered. It connects to the telephone line

via modular jacks and an alligator clip cordset. All results are shown on a

single high-contrast screen for simple and speedy usage. Measurements

are autoranging and true RMS. Functions include:

A. VOICE NETWORK TEST -- measures and simultaneously displays the

following phone line parameters:

1. DC Voltage

2. DC loop current

3. DC polarity

4. AC signals in either dBm or AC volts

5. Signal frequency

In a separate mode, the VNA-70A measures resistance:

6. Ohms in lop and DC

B. TONE GENERATOR -- generates a 1004 Hz sinewave.

C. DIGIT DISPLAY -- displays numbers as they are dialed.

D. AUDIO MONITOR -- allows input signals to be monitored via a built-in

speaker.

In connection with these features, the VNA-70A may be operated in

either of two modes:

LINE BRIDGING -- allows measurements to be made without loading

the phone line. Input signals may also be monitored via the built-in

speaker

LINE TERMINATING -- applies a precise 600 Ohm AC load to the line

while presenting a 50 to 300 Ohm effective DC resistance.

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3. CONTROLS

A. On/Off/Volume Control

B. Telephone Line Jack

C. Butt Set/CPE Jack

D. Setup Switch

E. Test Mode Switch

F. OHMS Switch

G. Audio Monitor Speaker

H. Display Screen; Super-Twist high contrast

I. Battery Charging Jack

J. Dial Pulse LEVEL SELECT

(Located inside battery compartment)

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Figure 3-1 Instrument Controls

4. OPERATION

4.1 Battery Test

When power is first turned on and the MODE switch is in the TEST

(UP) position, the VNA-70A will automatically enter the Battery Test mode.

During this brief period, it will measure the voltage of its own battery and

indicate this value on the Display Screen. The condition of the battery may

also be monitored at any time by observing the position of the cursor line

along the bottom of the display. The cursor begins on the right-hand side

of the screen with a new or fully charged battery; as the battery runs down,

the cursor moves towards the left. Replace the battery (or recharge if

rechargeable option is installed) when the cursor reaches the left-hand side

of the screen, or if the Battery Test at power-on reads below 6.5 Volts.

4.2 Bridging and Terminating

Using the SETUP switch, either a Line Terminating or a Line Bridging

test setup may be selected. The Line Terminating setup is equivalent to an

“off hook” condition on the phone line, and is selected by setting the switch to

the TERM (down) position. In this setup the VNA-70A presents a fixed 600

Ohm AC load and a variable 50 to 300 Ohm DC load to the line. The Line

Bridging test setup is the equivalent of an “on hook” condition on the phone

line, and is selected by setting the SETUP switch to the BRDG (center)

position. In this case the VNA-70A presents a high-impedance to the line.

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4.3 Voice Network Testing

The Voice Network Test mode is entered by placing the MODE switch in

the TEST (up) position. To make measurements:

a. Insert the modular plug on the test lead into the LINE jack.

b. Connect the test lead clips to telephone line Tip and Ring.

c. Plug a telephone or butt-set into the SET jack.

The following information will appear on the screen:

4.3.1 DC Voltage appears in the upper left-hand section of the screen.

A “+” or a “-“ precedes the voltage value shown to indicate its polarity.

The VNA-70A resolves voltage to the nearest ½ volt, therefore the

fractional DC voltage value is always a “.0” or a “.5”. An over range

condition is indicated by a ▲▲▲ reading.

4.3.2 DC Loop Current appears in the lower left-hand section of the

screen. A “+” or a “-“ precedes the current value shown to indicate its

polarity. The VNA-70A resolves current to the nearest ½ mA, therefore

the fractional DC current value is always a “.0” or a “.5”. An over range

condition is indicated by a ▲▲▲ reading.

_______________________________________________________

CAUTION

_______________________________________________________

OVERRRANGING THE DC MILLIAMMETER SECTION OF THE

VNA-70 FOR EXTENDED PERIODS MAY RESULT IN INTERNAL

DAMAGE.

4.3.3 dBm is displayed in the upper right-hand section of the screen.

With no input signal, an under range reading, indicated by▼▼▼,

is given. For signal inputs between -44 dBm and +4 dBm, the

“dB” mode is automatically selected. DB values are logarithmic in

scale; therefore resolution decreases with signal level.

This may be visualized by recalling the familiar scale of an analog

dB meter; indications are farther apart on the right-hand side and

get closer together toward the left-hand side. See the

SPECIFICATIONS section of this manual for dBm resolution at

various input levels.

4.3.4 AC Voltage replaces the dB indication when the input level is

above +4 dBm. In the AC Volts mode, readings may be taken up

to 125 Volts. An over range condition is indicated by a ▲▲▲

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reading. Both DBm and AC Volts measurements are made using

the True RMS conversion method and will give correct readings

even if distortion, multiple frequencies or noise are present.

4.3.5 Frequency of the input signal appears in the lower right=hand

section of the screen. The VNA-70A resolves frequency to the

nearest cycle. An over range condition is indicated by a ▲▲▲

reading. Note: due to noise, it is normal for a low frequency

reading to sometimes be displayed even with no input.

4.3.6 Tone Generator mode is entered by pushing the SETUP switch

up to TONE position. A “1004 Hz TONE” message appears on

the screen indicating selection of this mode. The sine wave

output should be taken from the LINE jack. Line termination is

maintained while the tone is on, making it an ideal reference tone

for transmission loss measurements. Tone output is at 0.0 dBm.

It also makes a handy “buzz box” for identifying wire pairs in multi-

line cables.

4.3.7 Resistance measurement to the nearest 100 Ohms is possible in

two different modes, depending upon the selection of the Ohms

switch:

LOOP OHMS is selected by moving the Ohms switch to the LOOP

(up) position. This mode gives the effective resistance of a

powered-up, or “Wet loop” by measuring voltage and current, then

calculating the resistance and displaying it on the screen. To use

this Feature:

a. Connect the phone line to the LINE jack, leaving the SET jack

unused.

b. Move the Ohms switch from the OFF (center) position to the

LOOP position.

c. Follow the prompts on the screen, first switching the SETUP

switch to BRDG, then to TERM. The calculated Ohms value

will appear on the display.

DC OHMS is selected by moving the Ohms switch to the DC (down)

position. The clip lead set should be connected to the LINE jack.

While the SET jack is left unused. The test lead clips may be

connected to measure the resistance of any un-powered, or “dry”

circuit.

4.4 Digit Display

4.4.1. Placing the MODE switch in the DIGITS (center) position selects

the Digit Display function. A flashing cursor in the upper left-hand corner

of the screen indicates selection of this mode. In most cases, it is

desirable to select the Line Bridging mode while using this feature.

To use the Digit Display:

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a. Insert the modular plug on the test lead into the LINE jack.

b. Connect the test lead clips to telephone line Tip and Ring.

c. Digits will appear on the screen at the location of the cursor. When

the first line of the display is full, the cursor will “roll-over” to the

second line. When the second line is full, the cursor will “roll” back

to the beginning of the first line. Therefore, if a digit string longer

than thirty-two digits in length is received, the last thirty-two digits

will be displayed.

d. Momentarily pushing the MODE switch down to the RESET position

will clear the display.

4.4.2. The VNA-70A provides two different sensitivity levels for dial pulse

detection. A switch located inside the battery compartment allows

selection of the level most appropriate to a given application. To

set the switch, remove the battery door on the back of the unit, and

hold it so that the battery compartment is to your left.

If the VNA-70A is to read pulse digits at a Central Office or at a D.I.D.

terminal, set the switch to the UP position.

If the VNA-70A is to be used in PBX systems having a 24-Volt battery

system, set the switch to the down position.

For digit monitoring at customer premises on standard 48-Volt

systems, either setting will work although it is generally preferable

to keep the switch in the down position unless CO/DID capability is

specifically required.

4.5. Monitor Speaker

The VNA-70A is equipped with a built-in monitor speaker, which may

be used at any time. Set its volume to the desired level using the

ON/OFF/VOLUME thumbwheel.

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5. POWER SOURCE

The VNA-70A is equipped with a 9-Volt rechargeable Ni-Cad battery.

When the battery runs down, recharge by inserting the plug from the

recharging transformer into the Battery Charger jack on top of the VNA-70A

and plugging the charging transformer into a 110 to 120-Volt AC source.

Recharging time is approximately 12 hours.

The VNA-70A may also be operated from a standard 9-Volt alkaline

battery. The battery is accessed by sliding off the removable cover on the

back of the case. CAUTION: DO NOT ATTEMPT TO USE THE

CHARGING TRANSFOMER IF AN ALKALINE BATTERY IS INSTALLED

IN THE VNA-70A. USE THE CHARGING TRANSFORMER ONLY WHEN

THE RECHARGEABLE NI-CAD BATTERY IS INSTALLED.

6. SPECIFICATIONS

Parameter Min Typ Max Unit

VOICE NETWORK ANALYZER:

DC Volts:

Range +/-1 +/-99.5 Volts DC

Resolution 0.5 Volt

Accuracy +/-1.0 % of FS

DC Milliamps:

Range +/-1 +/-99.5 mA DC

Resolution 0.5 mA

Accuracy +/-1.0 % of FS

AC Volts:

Range 3 125 Volts AC

Resolution 1 Volt

Accuracy +/-2.0 % of FS

Frequency Range 16 1K Hz

Conversion

Method True RMS

Decibels:

Range -44 +4 DBm

Resolution and

Accuracy:

-20 to +4 dBm 0.5 dB

-30 to -20 dBm 1.0 dB

-34 to -30 dBm 2.0 dB

-38 to -34 dBm 4.0 dB

-44 to -38 dBm 6.0 dB

Frequency Range 30 8K Hz

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