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INSTRUCTION MANUAL
MODEL 148A
2 0 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 I N 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, Calif. 92112
' Tel 7141279-2200 TWX 91w352oo7
hhuat l3eeion 6181
Instrument Retease A-3181
1.1 THE MODEL 148A External Trigger: Generator is quiescent until trig-
gered by an external signal, then generates one cycle
Wavetek Model 148A, 20 MHz AM/FM/PM Generator at the selected frequency.
is a precision source of sine, triangle, square, ramp
and pulse waveforms plus dc voltage. The waveforms External Gate: Same as external trigger, except gen-
may be controlled in symmetry as well as amplitude erator oscillates at the selected frequency for the
and dc offset. A built-in modulation generator can duration of the positive state of the external signal
modulate frequency, phase and amplitude or modula- plus the time to complete the last cycle.
tion may be by an external source.
Internal Trigger: Same as external trigger, except that
The generator may be run in continuous mode or trig- the modulation generator is internally connected to
gered for a single pulse or gated for a burst of pulses. the trigger input of the main generator.
Triggering and gating may be by the Model 148 built-in
modulation generator or by a n external source. The Internal Gate: Same as external gate, except that the
triggered and gated waveform start/stop point is modulation generator is internally connected to the
selectable from - 90' through + 90' Start/stop con-
. trigger input of the main generator.
trol plus dc offset control gives haverwave capability.
The main output of waveforms may be attenuated and 3 Modulation Modes
offset. A TTL sync pulse is available at main generator
frequencies, and the modulation generator waveforms Internal Modulation
are available at fixed amplitudes. Setting a front panel modulation switch in the INT
position routes the selected modulation function from
Frequency of both the main generator and the the modulation amplitude control to the selected mod-
modulation generator can be manually controlled at ulating circuits of the main generator.
the front panel or electrically controlled by external
voltages. Amplitude Modulation (AM): 2/ 2/ , `
L modu-
lation functions are used in this internal modulation
mode. With modulation amplitude ccw, carrier at
1.2 SPECIFICATIONS function output is not amplitude modulated and ap-
proximately half of normal (AM OFF) amplitude.
1.2.1 Main Generator Clockwise rotation of modulation amplitude results in
increasing amplitude modulation of the carrier to at
1.2.1.1 Waveforms least 100% AM.
S e l e c t a b l e s i n e % , triangle 2/ , square % , Frequency Modulation (FM) and Sweep: M and
positive square J-L , negative square U- and dc. A m modulation functions are used to linearly
TTL sync pulse is provided on a separate output con- sweep the main generator frequency. The frequency
nector. All can be produced with variable symmetry, dial sets the lower sweep limit and the modulation
amplitude and dc offset. amplitude control determines the upper frequency
limit (not to exceed 2.0 x multiplier). A sweep set
1.2.1.2 Operational Modes mode allows precision setting of upper frequency
limit. For frequency deviation, the dial determines the
Continuous: Generator oscillates continuously at the center frequency and modulator /\I , 2/ or \
selected frequency. varies the main generator frequency above and below
l-l
center by an amount determined by the modulation peak current and may be attenuated to 60 dB in 20 dB
amplitude. steps. An additional 20 dB vernier also controls the
waveform amplitudes.
-Phase Modulation (PM): As in External Modulation.
A m p l i t u d e o f m o d u l a t o r 2/ , 2/ , \ f u n c t i o n s 1.2.1.6 Adjustable Waveform Start/Stop Point
varies phase up to 250' .
Approximately - 90'to + 90' to 2 MHz (operative on
External Modulation sine and triangle waveforms only).
A BNC feeds an external signal to the modulating cir-
cuits when selected by a front panel modulation tog- 1.2.1.7 DC Output and DC Offset
gle switch in the EXT position.
Selectable through function output (5OQ). Controlled
Amplitude Modulation (AM): External modulating
by front panel controls to a minimum of
signals with zero dc component produce suppressed
t 14.4 Vdc( t 7.2 Vdc into 500) with signal peak plus
carrier modulation; i.e., a carrier (at main generator
offset limited to k 15 Vdc ( t 7.5 Vdc into 5OQ). DC off-
function output) amplitude of zero. The function out-
set and wave form attenuated proportionately by the
put modulated signal has an amplitude sensitivity of
60 dB output attenuator.
3 volts peak (1.5 Vp into 5OQ) per volt peak in. A car-
rier signal level at the function output can be pro-
1.2.1.8 External Modulation Input
duced at a sensitivity of 3 Vp (I .5 Vp into 500) per 1 Vp
dc component in. Modulating the dc component mod- AM: Sensitivity of 3 Vp out/Vp (1.5V into 503). Input
ulates the carrier level. Percent modulation (AM) will
impedance is >2.5 k0.
be the ratio of the peak ac to peak dc of the modulating FM: Sensitivity of 20% of frequency range/Vp. Input
signal. Input impedance is >2.5 kQ.
impedance is 5 kn.
PM : Sensitivity of IO0 phase shift/VP. Input im-
Frequency Modulation (FM) and Sweep: Sensitivity is
pedance is 1O kQ.
20% of frequency range/volt peak. Linear behavior
results only when all instantaneous frequencies call-
1.2.1.9 Symmetry
ed for fall within the frequency range (2 x multiplier
to 0.002 x multiplier). The instantaneous frequency
Symmetry of all waveform outputs is continuously ad-
called for is the multiplier and dial setting altered by
justable from 1 :1 9 to 19:1. Varying symmetry provides
the instantaneous voltage at the modulation input. In-
variable duty-cycle pulses, sawtooth ramps and non-
put impedance is 5 kQ.
symmetrical sine waves.
Phase Modulation (PM): Sensitivity is IO0 phase shift/
volt peak. Linear behavior results only when all instan- NOTE
taneous transition frequencies called for fall within
the frequency range (2 x multiplier to 0.002 x multi- When SYMMETRY control is used, in-
plier).The instantaneous frequencies called for will dicated frequency is divided by approx-
depend heavily on the modulation frequency. and ima tely IO.
waveform. Inoperative at frequency multiplier settings
below 100. Input frequencies roll off at 6 dB/octave 1.2.1.10 Sync Output (TTL)
above one half of full range frequency and above
150 kHz. Input impedance is IO kQ. TTL level pulse which will drive 10 TTL loads. Fre-
quency and time symmetry are the same as for func-
1.2.1.4, Frequency Range tion output.
0.0002 Hz to 20 MHz in IO overlapping ranges with 1.2.1.11 Trlgger and Gate
approximately 1 % vernier control.
Input Range: IV p-p to * IOV.
1.2.1.5 Function Output (500) Input Impedance: IO k0, 33 pF.
Pulse Width: 25 ns minimum.
s , 2/ and \ selectableandvariable to 30V p-p Repetition Rate: IO MHz maximum.
(15V p-p into 5Os1). n and u up to 15 Vp (7.5 Vp Adjustable triggered signal start/stop point: approxi-
into 5On). All waveforms and dc can supply 150 mA mately - 90'to +90" to 2 MHz.
1-2
1.2.1 .12 Frequency Precision 1.2.2.3 Output (6OOQ)
Dial Accuracy 2/ , 2/ and ` are fixed level 10V p-p balanced
L
+ (I O/O of setting + 1 % of full range) on x 100 thru
- about ground. M and M are fixed level 5 Vp
x 1 M ranges. from 0 to + 5V.
*+ (2% of setting + 2% of full range) on x .Ol thru
- 1.2.2.4 Frequency Modulation (FM IN)
x 10 and x 10M ranges.
Voltage control of modulator frequency with sensitivity
Time Symmetry of 20% of range per volt. Input impedance is 5 kQ.
t 0.5% on x 100 thru x IOOk ranges and from 0.2 to
1.2.2.5 Waveform Characteristics
2.0 on dial. '
t 5% on all other ranges and from 0.02 to 2.0 on dial.
Sine Distortion
<5 %
1.2.1 .13 Amplitude Precision
Amplitude Change With Frequency Time Symmetry
Sine variation less than: ' < O/O from 1 Hz to 10 kHz.
t 0.1 dB thru x 1 OOk ranges; 5 % from 0.1 Hz to 100 kHz.
-+ 0.5 dB on x 1 M range; 1.2.3 General
t 3 dB on x 10M range.
1.2.3.1 Stability (for amplitude, dc offset and
Step Attenuator Accuracy frequency)
+
- 0.3 dB per 20 dB step at 2 kHz. Short Term: t 0.05% for 10 minutes.
Long Term: t,O.25O/o for 24 hours.
1.2.1.14 Waveform Characteristics
1.2.3.2 Environmental
Sine Distortion
Specifications apply at 25