Wavetek 148A User Manual

INSTRUCTION MANUAL

MODEL 148A

MHz

AM/FM/PM GENERATOR

@ -

1981. - Wavetek

THIS DOCUMENT CONTAINS INFORMATION PRO-

PRIETARY TO WAVETEK AND IS SOLELY FOR IN-

STRUMENT OPERATION AND MAINTENANCE. THE

INFORMATION IN THIS DOCUMENT MAY NOT BE DUPLICATED IN ANY MANNER WITHOUT THE PRIOR APPROVAL IN WRITING OF WAVETEK.

SAN DIEGO

9045 Balboa Ave., San Diego, CA 92123 P.O. Box 661, San Diego,

’

Tel

7141279-2200

TWX 91w352oo7

Calif.

92112

hhuat

Instrument Retease

l3eeion 6181

A-3181

1.1 THE MODEL

Wavetek Model

148A

148A,

20 MHz AM/FM/PM Generator is a precision source of sine, triangle, square, ramp and pulse waveforms plus

voltage. The waveforms may be controlled in symmetry as well as amplitude and dc offset. A built-in modulation generator can modulate frequency, phase and amplitude or modulation may be by an external source.

The generator may be run in continuous mode or triggered for a single pulse or gated for a burst of pulses. Triggering and gating may be by the Model 148 built-in modulation generator or by

external source. The

triggered and gated waveform start/stop point is

- 90’

selectable from

through +

trol plus dc offset control gives haverwave

90’.

Start/stop con-

capability.

External Trigger:

Generator is quiescent until triggered by an external signal, then generates one cycle at the selected frequency.

External Gate: Same as external trigger, except generator oscillates at the selected frequency for the

duration of the positive state of the external signal plus the time to complete the last cycle.

Internal Trigger: Same as external trigger, except that

the modulation generator is internally connected to the trigger input of the main generator.

Internal Gate: Same as external gate, except that the

modulation generator is internally connected to the trigger input of the main generator.

The main output of waveforms may be offset. A TTL sync pulse is

available

attenuated

and

at main generator frequencies, and the modulation generator waveforms are available at fixed amplitudes.

Frequency of both the main generator and the modulation generator can be manually controlled at the front panel or electrically controlled by external

voltages.

1.2

SPECIFICATIONS

1.2.1

1.2.1.1

Main Generator

Waveforms

Selectable sine % , triangle 2/ , square % positive square

J-L ,

negative square U- and dc. A TTL sync pulse is provided on a separate output connector. All can be produced with variable symmetry, amplitude and dc offset.

1.2.1.2

Operational Modes

Continuous: Generator oscillates continuously at the selected frequency.

Modulation Modes

Internal Modulation

Setting a front panel modulation switch in the INT position routes the selected modulation function from the modulation amplitude control to the selected mod-

ulating circuits of the main generator.

Amplitude Modulation (AM):

lation functions are used in this

2/ , ‘L

internal

mode. With modulation amplitude ccw, carrier at

function output is not amplitude modulated and ap-

proximately half of normal (AM OFF) amplitude.

Clockwise rotation of modulation amplitude results in

increasing amplitude modulation of the carrier to at least 100% AM.

Frequency Modulation (FM) and Sweep:

modulation functions are used to linearly

sweep the main generator frequency. The frequency

dial sets the lower sweep limit and the modulation

amplitude control determines the upper frequency limit (not to exceed 2.0 x multiplier). A sweep set

mode allows precision setting of upper frequency

limit. For frequency deviation, the dial determines the center frequency and modulator varies the main generator frequency above and below

modu-

modulation

/\I , 2/

and

l-l

center by an amount determined by the modulation amplitude.

-Phase Modulation (PM): As in External Modulation. Amplitude of modulator varies phase up to

250’.

2/ , 2/ , \

functions

External Modulation

A BNC feeds an external signal to the modulating circuits when selected by a front panel modulation toggle switch in the EXT position.

peak current and may be attenuated to 60 dB in 20 steps. An additional 20 dB vernier also controls the waveform amplitudes.

1.2.1.6

Approximately sine and triangle waveforms only).

1.2.1.7

Adjustable Waveform Start/Stop Point

- 90’

to +

90’

to 2 MHz (operative on

DC Output and DC Offset

Amplitude Modulation (AM): signals with zero dc component produce suppressed carrier modulation; i.e., a carrier (at main generator function output) amplitude of zero. The function output modulated signal has an amplitude sensitivity of 3 volts peak (1.5 Vp into

rier signal level at the function output can be produced at a sensitivity of 3 Vp (I dc component in. Modulating the dc component mod-

ulates the carrier level. Percent modulation (AM) will be the ratio of the peak ac to peak dc of the modulating signal. Input impedance is

Frequency Modulation (FM) and Sweep: Sensitivity is 20% of frequency range/volt peak. Linear behavior

results only when all instantaneous frequencies called for fall within the frequency range (2 to 0.002 called for is the multiplier and dial setting altered by the instantaneous voltage at the modulation input. Input impedance is 5

Phase Modulation (PM): Sensitivity is volt peak. Linear behavior results only when all instantaneous transition frequencies called for fall within

the frequency range (2

plier).The

depend heavily on the modulation frequency. and

waveform. Inoperative at frequency multiplier settings

below 100. Input frequencies roll off at 6 dB/octave

above one half of full range frequency and above

150

1.2.1.4,

multiplier). The instantaneous frequency

instantaneous frequencies called for will

kHz.

Input impedance is IO

Frequency

5OQ)

kQ.

Range

External modulating

per volt peak in. A car-

Vp into 500) per 1 Vp

>2.5 kQ.

multiplier

IO0

phase shift/

multiplier to 0.002 x multi-

kQ.

Selectable through function output by front panel controls to a minimum of

14.4 Vdc( t 7.2 Vdc into offset limited to k 15 Vdc ( t 7.5 Vdc into set and wave form attenuated proportionately by the 60

output attenuator.

1.2.1.8

AM: Sensitivity of 3 Vp

impedance is FM: Sensitivity of 20% of frequency range/Vp. Input impedance is 5 PM

pedance

1.2.1.9

Symmetry of all waveform outputs is continuously adjustable from 1 variable duty-cycle pulses, sawtooth ramps and symmetrical sine waves.

External Modulation Input

>2.5 k0.

kn.

Sensitivity

is 1O

kQ.

Symmetry

9 to

When SYMMETRY control is used, indicated frequency is divided by ima

tely IO.

500)

out/Vp (1.5V

IO0

phase

19:1.

Varying symmetry provides

NOTE

(5OQ).

Controlled

with signal peak plus

5OQ).

DC off-

into 503). Input

shift/VP.

Input im-

non-

approx-

1.2.1.10 Sync Output (TTL)

TTL level pulse which will drive 10 quency and time symmetry are the same as for function output.

TTL

loads. Fre-

0.0002

approximately

1.2.1.5

(15V

into

1-2

Hz to 20 MHz in

Function Output

, 2/ and \ selectableandvariable

p-p into

5On).

5Os1). n

All waveforms and dc can supply 150

overlapping ranges with

vernier control.

(500)

and u up to 15 Vp (7.5 Vp

to 30V

p-p

1.2.1.11 Trlgger and Gate

Input Range: IV p-p to * Input Impedance: IO Pulse Width: 25 ns minimum. Repetition Rate: IO MHz maximum. Adjustable triggered signal start/stop point: approximately-

90’

+90”

IOV.

k0,

pF.

to 2 MHz.

1.2.1 .12

Frequency Precision

1.2.2.3

Output

(6OOQ)

Dial Accuracy

+ (I

O/O

of setting + 1 % of full range) on x 100 thru

x 1 M ranges.

*+ (2% of setting + 2% of full range) on

x 10 and x

10M

ranges.

.Ol

Time Symmetry

0.5% on x 100 thru x IOOk

2.0 on dial.

5% on all other ranges and from 0.02 to 2.0 on dial.

1.2.1

.13

’

Amplitude Precision

Amplitude Change With

Sine variation less than:

0.1 dB thru x 1

0.5 dB on x 1 M range;

3 dB on x 10M range.

OOk

ranges;

ranges and from 0.2 to

Frequency

’

Step Attenuator Accuracy

0.3 dB per 20 dB step at 2

1.2.1.14

Waveform Characteristics

kHz.

Sine Distortion

<0.5%

< All harmonics 30 range. All harmonics 26 dB below fundamental on x 10

range.

on x 100 Hz to x 10

.O%

on x

.01

to x 10 Hz and x 100

kHz.

kHz

ranges.

below fundamental on x I MHz

thru

MHz

, 2/ and ‘L are fixed level about ground. M and from 0 to +

1.2.2.4 Voltage control of modulator frequency with sensitivity

of 20% of range per volt. Input impedance is 5

1.2.2.5

5V.

Frequency Modulation (FM IN)

Waveform Characteristics

10V

p-p balanced

are fixed level 5 Vp

kQ.

Sine Distortion

Time Symmetry <

O/O

from 1 Hz

from 0.1 Hz to 100

to 10

kHz.

1.2.3 General

1.2.3.1

Stability (for amplitude, dc offset and

frequency)

Short Term:t 0.05% for 10 minutes.

Long Term:

1.2.3.2

Specifications apply at

will operate from

1.2.3.3

28.6

cm (11 ?4 in.) wide;

(103/4

in.) deep.

t,O.25O/o

for 24 hours.

Environmental

25°C t 5°C ambient

O°C

to 50°C ambient temperatures.

Dimensions

13.3

Instrument

(5 % in.) high; 27.3 cm

Square Wave Rise/Fall Times

FUNCTION

OUT < 25

ns for

15V

p-p into a

5Ost

load.

Triangle Distortion

Odd harmonics within 15% of correct value to 2 MHz.

1.2.2

Modulation Generator

1.2.2.1

Selectable sine 2/ , triangle ramp M and down ramp M

1.2.2.2

s,2/

ranges.

M, Nl

Waveforms

Frequency Range

Sweep:

Hzto100

0.1

0.2 Hz

square ?J , up

kHzz

200

kHz

(2 x setting).

three

100:1

1.2.3.4 5 kg (11 lb) net; 6.6 kg (14% lb) shipping.

1.2.3.5

90 to selectable;

Weight

Power

108 to

126V,

105V,,

48 to 400 Hz; less than 40 watts.

Unless otherwise noted, ail specifications apply from when FUNCTION OUT is at maximum and

5OQ

terminated, with SYMMETRY control at OFF. Symmetry and vernier affect frequency calibration. Maximum possible asymmetry is a function of frequency setting.

198 to 231V and 216

NOTE

0.1

to 2.0 on frequency dial

252V

1-3

SECTION

OPERATION

3.1 CONTROLS AND CONNECTORS

The following item

3.1

Main Generator

Frequency Dial

main generator.The setting on this dial multiplied by the FREQ MULT basic output frequency of the generator at the

FUNCTION OUT.6 and SYNC OUT 7 The FREQ VERNIER the modulation generator also affect the main generator frequency.

Mode

Switch

operating mode of the main generator as follows: a.

EXT GATE Mode

quiescent until a proper gate signal is applied at the EXTTRIG IN BNC 13 and then outputs

the selected signal for the duration of the gate

signal, plus the time to complete the last cycle

generated.

numbers are keyed

The

This outer switch selects the

frequency control of the

and, in some cases,

The main generator is

to figure

setting is the

3-1.

BNCs.

b. EXT TRIG

mode, except the main generator output is one cycle of selected signal only.

c. CONT Mode - The output signal is continuous.

INT TRIG -

cept the trigger signal is applied internally by

the modulation generator.

e. INT GATE

the gate signal is applied internally by the modulation generator.

TRIGGER LEVEL

is a continuously variable adjustment of the trigger circuitry firing point. When full ccw, a

tive going pulse at approximately quired for triggering (see figure

cw position,

mately + quired for triggering. In the GATE modes, the‘ generator will run continuously when the control

is cw of 12 o’clock.

Mode

Same as for EXT GATE

Same as for EXTTRIG mode, ex-

Same as for

Control -

positive going pulse at approxi-

7.5V

or more positive voltage is re-

EXT GATE,

This

inner control

7.5V

3-2).

In the full

except

posi-

re-

12 13

Figure 3-1

Controls

MOOULATION

and Connectors

GENERATOR

3-1

3.1.2

Modulation

FUNCTION Switch

Generator

This switch selects the waveform output of the modulation generator. Output is at the OUT BNC connector also available internally to the main generator. Waveforms are sine square

(N\).

AMPLITUDE

sweep frequency.

( ‘% ),

ramp up (M) and ramp down

A SWP SET detent holds the OUT BNC at

control 14 level;

( /L ),

triangle

used

to set upper

and is

( 2/ ),

AM- The instantaneous amplitude of the out-

put signal varies with the instantaneous ampli-

tude of the modulation signal.

FM- The instantaneous frequency of the output signal varies with the instantaneous amplitude of the modulation signal.

PM- The instantaneous phase of the output signal varies with the instantaneous amplitude of the modulation signal.

MOD AMPLITUDE Control - This inner con-

trol attenuates the modulation generator signal that is internally fed to the main generator when modulating. It has no effect during internal triggering or gating and it has no effect on the

OUT

FREQ/PERIOD

signal.

MULT Switch - This outer switch (with ranges given in both frequency and period) selects the modulation generator frequency/

period range.

VARIABLE Control

This inner control sets

the frequency/period within a range.

OUT

(6OOn)

Connector - This BNC is the

modulation generator waveform output: sine

( % ),

triangle

level

1OV p-p

balanced about ground and ramp

( 2/ )

and square

(5V p-p into

6OOQ)

waveforms

( ‘L )

fixed

( AA, M )

fixed level 0 to + 5 Vp waveform. FM IN (5

kQ)

Connector - This BNC is

the input for frequency modulation of the modulation generator.

Sensitivity is 20% of frequency range

per volt in.

OPERATlON

convenience,

For

the generator operation has been grouped in seven basic modes, from which many variations and combinations are possible. The following paragraphs give basic switch positions for each mode and requirements and suggestions for operation.

3.2.1 When setting up the generator, it is advisable to

serve the output on an oscilloscope. Connect TION

5OQ

The dc output can be set from + 15 Vdc

- 15

Vdc (+ 7.5 Vdc to - 7.5 Vdc into

5OQ).

Continuous Operation

ob-

FUNC-

OUT to the scope input using a 500 cable and a

load. For continuous waveform output, select a basic waveform at the desired frequency. Ensure the modulation switches are set to OFF and the mode is set to

CONT.

The output amplitude can be as great as

15V p.p;

attenuate as desired.

NOTE

use

For best waveform quality, TENUATIO N tion; then use

SWITC H

the

for gross attenua-

AMPLITUDE control for

the AT-

fine attenuation.

The waveform may be skewed to the left or right using the SYMMETRY control; e.g., making a ramp from a triangle

(

waveform.

( ,/1 )

NOTE

The output frequency is divided b y

when

the SYMMETRY control is switched from

the OFF position.

The dc level of the waveform may be varied with the

DC OFFSET control, but waveform clipping can occur.

NOTE

The basic modes of operation are:

Continuous- A continuous output signal.

Triggered

One cycle of waveform for each

trigger signal.

Gated

A “burst” of waveforms for the dura-

tion of each gate signal.

Waveform clipping will occur (OVERLOAD

LED will light), unless waveform amplitude

is decreased so

that

wavefor m

plus

offset

is less than 7.5 volts at the waveform peak.

3.2. 2

Triggered Operation

In triggered operation, there is one cycle of output for

each trigger signal input. For triggered operation, first

3-3

set up the generator for continuous operation (refer to paragraph 3.2.1). The main generator may be trig-

gered internally by the modulation generator or trig-

gered by an external source. If an unmodulated waveform is being output, the modulation generator is

free. to give the desired triggering frequency and

should be selected as the trigger source. Use any

modulation generator waveform as the trigger. Set the modulation generator frequency for the desired trigger frequency and sync on the modulation generator output.

NOT E

3.2.4

The TRIGGER LEVEL control manually triggering or gating the generator. For

manually triggering (single cycles), the generator

mode should be EXT TRIG with no external signal input at the EXT TRIG IN connector. Each time TRIGGER LEVEL is rotated cw through mid-position, one triggered cycle will be generated. In EXT GATE mode, the generator runs continuously as long as the TRIGGER LEVEL is

Manual Triggering and Gating

can also be used

of mid-position.

for

1. Trigger frequency must be slower than the output waveform frequency.

The MOD AMPLITUDE control has no effect in

Rotate the TRIGGER LEVEL control to obtain a good trigger. If the waveform start/stop point is to be other than zero degrees, set the TRIG START/STOP control as required. (See figure 3-3.) Haverwaves can be set

up using start/stop control and

-90°

s--

If external triggering is to be used, connect a repetitive signal with a positive going transition of greater than one volt to EXT TRIG IN using a the TRIGGER LEVEL control for proper triggering.

3.2. 3

In gated operation there is a “burst” of waveforms lasting the duration of the gate pulse plus the time required to complete the last cycle of waveform started. Set up as for triggered operation (refer to paragraph 3.2.2) and select a “trigger” signal whose duty time gives the desired waveform burst.

Figure

Gated Operation

INT

TRIG

and INT GATE modes.

offset control.

HAVERSINES

3-3..

Waveform Start/Stop Examples

5OQ

cable. Adjust

3.2.5

AM Operation

In amplitude modulation, the instantaneous amplitude of the output signal varies with the instantaneous amplitude of the modulation signal.

NOT E

The output waveform will be LOAD LED will light) if any instantaneous amplitude greater tha n ( t

7.5 volts into

Set up the generator as for continuous operation (refer to paragraph 3.2.1). Switch to internal or external amplitude modulation. If internal, note that the car-

rier (main generator waveform) mean amplitude is decreased to half. This is to prevent clipping driving the output amplifier) when the carrier amplitude is modulated (increased and decreased) by another signal. Set the modulation generator frequency to a lower frequency than the main generator and sync the scope to the modulation generator output. Set the modulator amplitude for a desired percentage of amplitude modulation (0 to greater than 1 and set the main generator ATTENUATION and AMPLITUDE controls for a desired amplitude of modulated waveform. If external modulation is selected, observe that the carrier (main generator waveform) amplitude drops to zero (null). This is for suppressed carrier mode of amplitude modulation. Connect the modulator OUT

IN with a coaxial cable. Set the main generator ATTENUATION and AMPLITUDE controls amplitude of suppressed carrier waveform. For best

results when using an external modulation signal at

EXT MOD IN, maintain as near as convenient amplitude (which does not exceed 5 main generator ATTENUATION and AMPLITUDE controls. An external source may also be used for regular AM operation, rather than suppressed carrier operation, by supplying a dc component along with the ac

5OQ )

is produced.

clipped(OVER-

15 volt s

(6OOQ)

to the EXT MOD

VP);

(over-

00%

range)

for

a desired

5 Vp

then use the

3-4

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