Tenma 72-6859 User Manual

72-6859

20MHz FUNCTION GENERATOR

INSTRUCTION MANUAL

Tenma 72-6859 Instruction manual

Table of Contents

Introduction 2

Specification 2

EMC 5

Safety 4

Installation 5

Operation 7

Maintenance 8

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Tenma 72-6859 Instruction manual

This instrument is a 20MHz function generator with waveforms of sine, square, triangle, ramp,
pulse and DC from a variable amplitude 50Ω output. A TTL output is also provided.

The frequency range is 0.2Hz to 20MHz selected by an eight decade range multiplier and
calibrated vernier. The sweep input can be used to give a >20:1 frequency change within a
selected range.

The generator output level is 20Vpk-pk maximum from a 50Ω source. The level is set via
switched attenuators plus vernier with a total range of 66dB. DC offset is vernier adjustable over a
±10V range with 0V defined by a centre detent.

A switchable symmetry control with a 6:1 range permits ramp and pulse waveforms to be
produced.

FREQUENCY

Frequency Range: 0.2Hz to 20MHz in 8 overlapping decade ranges with fine adjustment

by a vernier.
Vernier Range: >10:1 on each range.
Vernier Accuracy: Typically ± 5% of full scale.

Introduction

Specification

SWEEP MODE (EXTERNAL)

Sweep Range: Typically >20:1.
Input Impedance:
Input Sensitivity: Typically 0 to 2V for 10:1 sweep.
Maximum Allowable

Input Voltage:
Maximum Slew Rate of

sweep voltage:

OPERATING MODES

(Specifications apply for the top decade of each frequency range and output 10V peak-to-peak
into 50Ω termination).

Sine

Distortion: Typically 2% on 200, 2k and 20k ranges.
Amplitude Flatness: ± 0.2dB to 200kHz; ± 2dB to 20MHz.

Triangle

Linearity: Typically 99% on kHz ranges.

Squarewave

82 kΩ

± 10V

0.1V/us

Rise and Fall Times: <22ns

DC

Range:

±10V from 50Ω

Symmetry

Symmetry Range: Typically variable from 1:6 to 6:1 up to 500kHz.

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Tenma 72-6859 Instruction manual

OUTPUTS

50Ω

Three switch-selectable ranges with 26dB vernier control within each attenuator range.

0dB Range:

1V to 20V peak-to peak from 50Ω (0.5V to 10V into 50Ω).

–20dB Range:

–40dB Range:

DC Offset Control Range:

TTL

Capable of driving 4 standard TTL loads.

GENERAL

Power: 230V or 115V nominal 50/60Hz, adjustable internally; operating

Operating Range: + 5ºC to +40ºC, 20% to 80% RH.

Storage Range:

Environmental: Indoor use at altitudes up to 2000m, Pollution Degree 2.

Electrical Safety: Complies with IEC 1010-1

EMC: Complies with EN50081-1 and EN50082-1

Size: 220(W) x 82(H) x 230(D) mm, (10.3 x 3.4 x 9.2”) excluding feet.

100mV to 2V peak-to-peak (50mV to 1V into 50Ω)

10mV to 0.2V peak-to-peak (5mV to 0.1V into 50Ω)

±10V from 50Ω. DC offset plus signal peak limited to ±10V
(± 5V into 50Ω). DC offset plus waveform attenuated proportionally in

−20dB and −40dB position.

range ±14% of nominal; 30VA max. Installation Category II.

−40ºC to +70ºC

Weight: 1.5 kg (3.3lb).

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Tenma 72-6859 Instruction manual

This instrument is Safety Class I according to IEC classification and has been designed to meet
the requirements of IEC 1010-1 (Safety Requirements for Electrical Equipment for Measurement,
Control and Laboratory Use). It is an Installation Category II instrument intended for operation
from a normal single phase supply.

This instrument has been tested in accordance with IEC 1010-1 and has been supplied in a safe
condition. This instruction manual contains some information and warnings which have to be
followed by the user to ensure safe operation and to retain the instrument in a safe condition.

This instrument has been designed for indoor use in a Pollution Degree 2 environment in the
temperature range 5°C to 40°C, 20% - 80% RH (non-condensing). It may occasionally be
subjected to temperatures between +5°C and –10°C without degradation of its safety. Do not
operate while condensation is present.

Use of this instrument in a manner not specified by these instructions may impair the safety
protection provided. Do not operate the instrument outside its rated supply voltages or
environmental range.

WARNING! THIS INSTRUMENT MUST BE EARTHED

Any interruption of the mains earth conductor inside or outside the instrument will make the
instrument dangerous. Intentional interruption is prohibited. The protective action must not be
negated by the use of an extension cord without a protective conductor.

Safety

When the instrument is connected to its supply, terminals may be live and opening the covers or
removal of parts (except those to which access can be gained by hand) is likely to expose live
parts. The apparatus shall be disconnected from all voltage sources before it is opened for any
adjustment, replacement, maintenance or repair.

Any adjustment, maintenance and repair of the opened instrument under voltage shall be avoided
as far as possible and, if inevitable, shall be carried out only by a skilled person who is aware of
the hazard involved.

If the instrument is clearly defective, has been subject to mechanical damage, excessive moisture
or chemical corrosion the safety protection may be impaired and the apparatus should be
withdrawn from use and returned for checking and repair.

Make sure that only fuses with the required rated current and of the specified type are used for
replacement. The use of makeshift fuses and the short-circuiting of fuse holders is prohibited.

Do not wet the instrument when cleaning it.

The following symbols are used on the instrument and in this manual:-

Caution -refer to the accompanying documentation, incorrect operation may
damage the instrument.

terminal connected to chassis ground.

mains supply OFF.

l

mains supply ON.

alternating current.

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Tenma 72-6859 Instruction manual

This function generator has been designed to meet the requirements of the European EMC
Directive 89/336/EEC.

Compliance was demonstrated by meeting the test limits of the following standards:

Emissions

EN50081-1 (1992) Generic emission standard for residential commercial and light
industry. Test methods and limits used were:

a) EN55022 Conducted, Class B

b) EN55022 Radiated, Class B

Immunity

EN50082-1 (1992) Generic immunity standard for residential, commercial and light industry.
Test methods and limits used were:

a) EN60801-2 (1993) Electrostatic Discharge, 8 kV air discharge.

b) IEC801-3 (1984) RF Field, 3 V/m.

c) IEC801-4 (1988) Fast Transient, 1 kV peak (AC line), 0.5kV peak (signal lines).

EMC

Cautions

To ensure continued compliance with the EMC directive the following precautions should be
observed:

a) connect the generator to other equipment using only high quality, double-screened

cables.

b) after opening the case for any reason ensure that all signal and ground connections

are remade correctly before replacing the covers. Always ensure all case screws are
correctly refitted and tightened.

c) In the event of part replacement becoming necessary, only use components of an

identical type, see the Service Manual.

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Tenma 72-6859 Instruction manual

Mains Operating Voltage

The operating voltage of the instrument is shown on the rear panel. Should it be necessary to
change the operating voltage from 230V to 115V or vice-versa, proceed as follows:

1. Disconnect the instrument from all voltage sources.

2. Remove the 4 screws which hold the upper and lower case halves together and lift off the

case upper.

3. Change the transformer connections following the diagrams below.

230V Operation - Primaries in series

Installation

115V Operation - Primaries in parallel

4. Reassemble in the reverse order.

5. To comply with safety standard requirements the operating voltage marked on the rear

panel must be changed to clearly show the new voltage setting.

Mains Lead

WARNING! THIS INSTRUMENT MUST BE EARTHED

Any interruption of the mains earth conductor inside or outside the instrument will make the
instrument dangerous. Intentional interruption is prohibited.

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Tenma 72-6859 Instruction manual

Power

The ON/OFF switch is on the rear panel of the instrument.

Frequency Selection

Frequency range is selected by an eight position multiplier switch with fine adjustment by
calibrated vernier.

Symmetry

A slide switch selects the symmetry control which varies the duty cycle 1:6 to 6:1 to produce
sawtooth and variable pulse-width waveforms.

Note: The symmetry of the Aux Output does not vary when Sine or Triangle are selected
because the Aux Output is generated by a zero crossing comparator.

Function Selection

The output waveform shape is selected by a four position switch to give sine, square, triangle and
DC. A DC level only is useful as it permits input threshold testing of a circuit without having to
connect up an external supply.

Operation

Main Output

The amplitude of the 50Ω MAIN output is controlled by the 3-position ATTENUATOR switches
and AMPLITUDE control. Maximum output is 20 volts peak-to-peak from 50Ω and 10 volts peak­to-peak when terminated with a 50Ω load.

The AMPLITUDE control has greater than 26dB range and used in conjunction with the
ATTENTUATORS a range of 0dB to −66dB can be achieved. This provides a range of 20V peak­to-peak down to 10mV peak-to-peak, or 10V peak-to-peak down to 5mV peak-to-peak into 50Ω.

Greater attenuation can be achieved by using standard 50Ω BNC attenuators. To maintain
waveform integrity only 50Ω cable should be used and the receiving end should be terminated
with a 50Ω load. The 50Ω MAIN output will withstand a short circuit for a period of 2 minutes at
maximum output and greater periods at lower output levels.

Do not apply external voltages to this output.

DC Offset

The DC OFFSET control has a range of ±10 volts from 50Ω in all output modes; the control has a
centre detent for 0 volts. DC offset plus signal peak is limited to ± 10V (± 5V into 50Ω). DC offset
plus waveform is attenuated proportionally in the −20dB and −40dB positions.

Aux Output

The AUX output provides a fixed TTL pulse output at the same frequency and phase as the
50Ω MAIN output and is capable of driving 4 standard TTL loads.

Sweep Input

The generator frequency can be swept, DC programmed or modulated by a suitable control
voltage applied to the SWEEP IN socket. The instrument sums the SWEEP IN voltage with the
internal control voltage derived from the FREQUENCY vernier to determine the operating
frequency. A positive voltage increases the frequency; for frequency control with positive-going
DC inputs the vernier should therefore be set to the lower frequency limit of the range to be
swept. For example, a 0V to +2V signal will sweep the generator 1 decade up from range
minimum, set by the vernier, to range maximum.

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Tenma 72-6859 Instruction manual

Similarly, a negative voltage decreases the frequency and for negative-going DC inputs the
vernier should be set to the upper frequency limit of the range to be swept. For example, a 0V to

−2V signal will sweep the generator 1 decade down from range maximum, set by the vernier, to
range minimum.

To use a sweep signal which is symmetrical about ground, the vernier should be set to give a
frequency at approximately the centre of the band to be swept.

Do not apply external voltages exceeding ±10V.

For service repair and calibration please contact your local Tenma distributor or go to

www.tenma.com

Cleaning

If the instrument requires cleaning use a cloth that is only lightly dampened with water or a mild
detergent.

Maintenance

WARNING! TO AVOID ELECTRIC SHOCK, OR DAMAGE TO THE INSTRUMENT, NEVER
ALLOW WATER TO GET INSIDE THE CASE. TO AVOID DAMAGE TO THE CASE NEVER
CLEAN WITH SOLVENTS.

Mains Fuse

The transformer primary is protected by an integral thermal fuse which is not user replaceable.
Should a fault develop which causes the thermal fuse to blow, the generator must be returned to
the manufacturer or agent for service.

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TEST EQUIPMENT

405 Pioneer Blvd.

Springboro, Ohio 45066

Book Part No. 48591-0730 Issue 1