Tektronix FG501 User manual

Tektronix, Inc.
p.10. Box 500
Beaverton, Oregon 97077
COMMITTEDTO EXCELLENCE
INSTRUCTION MANUAL
Serial Number
First printing August 1972

TABLE OF CONTENTS
SECTION 1 OPERATING INSTRUCTIONS
SECTION
2 SPECIFICATION AND PERFORMANCECHECK
Page
1-1
2- 1
I WARNING )
THE FOLLOWING SERVICING INSTRUCTIONS ARE FOR USE BY QUALIFIED PER-
SONNEL ONLY. TO AVOID PERSONAL INJURY, DO NOT PERFORM ANY SERVICING
OTHER THAN THAT CONTAINED IN OPERATING INSTRUCTIONS UNLESS YOU ARE
QUALIFIED TO DO SO.
SEICTION 3 ADJUSTMENT 3-1
SE:CTION 4 MAINTENANCEAND INTERFACING INFORMATION 4- 1
SE:CTION 5 CIRCUIT DESCRIPTION 5- 1
SE:CTION 6 OPTIONS 6- 1
SECTION 7 REPLACEABLEELECTRICAL PARTS 7- 1
SEiCTlON 8 DIAGRAM AND CIRCUIT BOARD ILLUSTRATION 8-1
SEICTION 9 REPLACEABLEMECHANICAL PARTS AND EXPLODED VIEW 9-1
CHANGEINFORMATION

Fig. 1-1. FG 501 Function Generator
REV. B JUL 1978

Section 1-FG 501
INSTRUCTIONS
INTRODUCTION
The FG !501 FunctionGenerator isdesignedtooperate
in a
TM 500-Series power module. Low distortion sine,
square,tria~ngle,pulse,andrampwaveformsfrom0.001
Hz
to 1 MHz as well as a $2.5 volt square-wave trigger are
available atthefront panel.Variable DCoffset ofk7.5volts
is also provided. A "hold1' feature allows the generator
output to be abruptly halted at its instantaneous voltage
level and held there until manually switched on again.
A voltage-controlled frequency (VCF)inputisprovided
to control the output frequency from anexternal voltage
source. The output frequency can be swept above or
below the selected frequency to a maximum of 1000:l
depending onthe polarityandamplitudeof the VCF input
and the selected output frequency.
Also included is an external gate input that allows the
generator to beturned onforthe durationof an externally
applied gating signal. This mode provideseither a single
cycle output or a train (burst) of preselected waveforms
depending on the gating signal width and the generator
frequency setting. The phase (startlevel) of thewaveform
burst can be varied
k90° by a front-panel control.
The variety of swept and modulated signals available
from the IFG 501 make it especially useful for such
applications as testing servo-system or amplifier
response, distortion, and stability; FM generation and
frequency multiplication; or simply used as a variable
beat-frequency oscillator, repetition-rate, or tone-burst
generator. 'The square-wavetrigger output can beusedas
a source for transistor-transistor logic (TTL) or to syn-
chronize an external device such as an oscilloscope
or
counter.
The FG 501 is calibrated and ready for use when
received. Itisdesignedtooperateinanycompartment of
a
TM 500-Series power module only. Refer to the power
module Instruction Manual for line voltage requirements
- and power module operation.
Installation and Removal
CAUTION
D
Turnthepower module off beforeinsertingtheplug-
in; otherwise, damage may occur to the plug-in
circuitry. Because of the high current drawn by the
FG
507, it is also recommended that the power
module be turned off before removing the FG
507.
Refer to Fig. 7-2. Check to see that the plastic
barriers on the interconnecting jack of theselected
power module compartment match the cut-outs in
the
FG 501 circuit board edge connector.
Align the FG 501 chassis with the upper and lower
guides of the selected compartment. Pushthe module in
and press firmly to seat the circuit board in the inter-
connecting jack.
Pull the Power switch on the front panel of the power
module to apply power to the FG 501. Observe that the
POWER indicator light on the FG 501 comes on.
Removethe FG 501 from the power module by pulling
the release latch at the bottom of the front panel and
sliding the unit straight out of the power module.
InterconnectingJack
Bottom Groove
Fig.
1-2. Plug-in installationand removal.
REV. C JUL 1978

Operating Instructions-FG 501
OPERATING CONSIDERATIONS
NOTE
Before using the FG 501 for the first time, read the
Operating Considerations in this section and the
description of the front-panel controls, connectors,
and indicators in Fig.
1-3.
Output Connections
The output of the FG 501 is designed to operate as a
voltage source inseries with 50
f2 andworking intoa 50 f2
load. At the higher frequencies, an unterminated or
improperly terminated output will cause excessive
aberrations on the output waveform (see lmpedance
Matching discussion).Loadslessthan50Rwill reducethe
waveform amplitude.
Excessive distortion or aberrations due to improper
termination is lesslikely tooccur at thelowerfrequencies
(especiallywith sineandtrianglewaveforms). However,to
ensure that waveform purity is preserved, observe the
following precautions:
1. Use quality 50
f2 coaxial cables and connectors.
2. Makeall connections tight andas short as possible.
3. Use quality attenuators, if necessary, to reduce
waveform amplitude to sensitive circuits.
4. Useterminators or impedance-matching devicesto
avoid reflections when using long cables, i.e., six feet or
more.
5. Ensure that attenuators, terminations, etc. have
adequate power-handling capabilities for the output
waveform (approximately 0.5 W into a 50
f2 load).
Power output isdetermined bytheselected waveform,
itsamplitude, and the amount of offset voltage selected.
Thephysical and electricalcharacteristicsof thepulse-
transmitting cable determine the characteristic im-
pedance, velocity of propagation, and amount of signal
loss. Signal loss, due to energy dissipation in the cable
dielectric, is proportional to the frequency; therefore, a
few feet of cable can attenuate high-frequency informa-
tioninafast-rise pulse.Itisimportanttokeepthesecables
as short as possible.
When signal comparison measurements or time
difference determinations are made, the twosiignalsfrom
the test device should travel through coaxial cables with
identical loss and time-delay characteristics.
Ifthereisadcvoltage acrosstheoutput load,theoutput
pulse amplitude will be compressed; or insorne cases, if
the voltage exceeds
f 10 V, it may short the output. To
prevent this from occurring, the output must be coupled
through a dc blocking capacitor to the load. The time
constant of the coupling capacitor and load must belong
enough to maintain pulse flatness.
Risetime and Falltime
If the output pulse from the FG 501 is used for
measuring the rise or falltime of a device, the risetime
characteristics of associated equipment may have to be
considered. If the risetime of the device under test is at
least 10times greater than the combined risetimesof the
FG 501 plus the monitoring oscilloscope and associated
cables, the error introduced will not exceed 1% and
generally can be ignored. If the rise or falltime of the test
device, however, is less than 10 times as long as the
combined risetimes of the testing system, the actual
/-
risetimeof the device will havetobedeterminedfromthe
risetime of each component making up the system. This
equals the square root of the sum of the squares of the
individual risetimes. Conversely,therisetimeof thedevice
under test can be found from the same relationship if all
theactual risetimes inthesystemareknownexceptthatof
the device under test.
lmpedance Matching
Reflections. As a pulse travels down a transmission
line, eachtime itencountersamismatch,or animpedance
different than the transmission line, a reflection is
generated and sent back alongthe linetothe source. The
amplitude and polarity of the reflections are determined
by the amount of the encountered impedance inrelation
to the characteristic impedance of the cable. If the
mismatch impedance is higherthantheline,thereflection
will be of the same polarity as the applied signal; if it is
lower, the reflection will be of opposite polarity. If the
reflectedsignal returns beforethe pulseisended, itadds
to or subtracts from the amplitude of the pulse. This
distorts the pulse shape and amplitude.
MatchingNetworks.
Thefollowingdescribes methods
for matching impedance networks into relatively low
impedances. If the FG 501 is driving a high impedance,
--
such as the 1 MR inputimpedanceof the vertical inputfor
an oscilloscope,thetransmission linemust beterminated
REV. B JUL 1978

Operating Instructions-FG 501
Fig. 1-3. Operating controls and connectors.
REV C, MAR 1979

Operating Instructions-FG 501
into a 50 f2 attenuator and a 50 f2 termination at the
oscilloscope input. The attenuator isolates the input
capacity of the device. Distortion can be caused bythis
input capacity.
A simple resistive impedance-matching network that
provides minimumattenuation isillustrated inFig. 1-4. To
match impedancewith the illustrated network,thefollow-
ing conditions must exist:
(R1
+ Z2)R2must equal zI
Ri + Z2+ R2
and
RI + - 'IR2 must equal ~2
ZI + R2
Therefore:
R1R2
= 2122;and RIZl = R2(Z2 - Z1)
For example;tomatcha 50
f2 system toa125 f2 system,
Z1equals 50
Cl and Z2 equals 125 0.
Therefore:
and R2
1 50dT125 - 50 = 64.6 f2
When constructing such a device, the environment
surrounding the components should also be designed to
provide a transition between the impedances. Keep in
mindthat the characteristic impedanceof acoaxialdevice
isdetermined bythe ratio betweentheoutsidediameter of
the inner conductor to the inside diameter of the outer
conductor.
z, = 1381
E loglo Dld, where D isthe inside
diameter of the outer conductor, and d is the outside
diameter of the inner conductor. E isthe dielectric cons-
tant (1 in air).
Attenuation Ratios.
Though the network in Fig. 1-4
provides minimum attenuation for a purely resistive
impedance-matching device,theattenuation asseenfrom
one end does not equal that seen from the other end.
A
signal (El) applied from the lower impedance source (Z1)
encounters a voltage attenuation (A1)which is greater
than 1 and less than
2, as follows:
Zl
-
(Low)
2
-
(High)
Fig. 1-4. Impedance-matching network that provides minimum
attenuation.
A signal (E2) appliedfromthehigher impedancesource
(22) encounters a greater voltageattenuation
(A2) which is
greater than 1 and less than 2 (Z~IZI):
Inthe example of matching 50
f2 to 125 f2.
The illustrated network can be modified to provide
different attenuation ratios by adding anot.her resistor
(less than R1)between Z1and the junction of R1and R2.
Duration of Ramps and Pulses
The duration of ramp and pulse waveforrns is always
equal tothe half-cycle time of thesine, square, ortriangle
waveform frequency. For MULTIPLIER setti~ngsof 1 or
greater,the retraceloff time issuchthat thewaveformhas
a duty cycle of approximately 80°/o, i.e., frequency equals
approximately 1.6X FREQUENCY
Hz dial setting. For
MULTIPLIER settings less than 1, the retrace/off time is
from 10 ms to 100 ms, which results in duty cycles
---
approaching 10O0/0;i.e., frequency equals approximately
2X FREQUENCY
Hz dial setting.
REV. B JUL 1978

Operating Instructions-FG 501
OPERATION
-A
Free-Running Output
The following procedure provides a free-running
waveform output with variable frequency and amplitude.
1. Set the AMPL control tothe fully counterclockwise
position and the OFFSET control to the 0 (centered)
position. Check that the PHASEcontrol ispushedin(off).
2. Set the FUNCTION selector to the desired
waveform (see Fig. 1-5).
Fig. 1-5. Output waveforms availablefrom the FG 501.
3. Select the desired frequency withthe MULTIPLIER
selector and FREQUENCY Hz dial. For example, if the
MULTIPLIER selector is set to the
lo5 position and the
FREQUENCYHz dial is at 5, output frequency is500 kHz;
i.e., MULTIPLIER setting
X FREQUENCYHz setting. The
output frequency is calibrated when the FREQUENCY
VERNIER control is in the fully clockwise position. The
durationof rampand pulsewaveforms isdependent onthe
MULTIPLIER setting. See Duration of Rampsand Pulses
under Operating Considerations for further information.
4. Connect the load to the OUTPUT connector and
adjust theAMPL control for the desired output amplituae.
Variable DC Offset
Pull outwardon theOFFSETcontrol (pullswitchadded
at SN B020000) to position the dc level (baseline) of the
output waveform. Forexample,$5
V of offsetwill increase
the dc
+ peak ac voltage of a 7.5 V p-p output to+5 and
+ 12.5 V dc .t peak ac while -5 V of offset will reducethe
dc
+ peak ac output to +2.5 V and -5 V.
Gated (Burst) Output and Variable Phase
A gating signal of 2 to 15 V amplitude applied to the
GATE INPUT connector with the PHASE control pulled
out will provide a burst of cycles at the OUTPUT
connector. Thedurationof theburstand number of cycles
inthe burst depend on the gating signal durationandthe
output frequency selected.Whenthegatingsignal goesto
the zero level, the generator completes its last cycle and
remains quiescent until the next gating signal.
Single cycles can be obtained by applying a gating
signal with a periodapproximately equal tothe period of
the FG 501 output waveform. The number of cycles per
burst can be approximated by dividing the gating signal
duration by the period of the FG 501 output frequency
GATE INPUT
PHASE
control at 90" LAG
GATE INPUT
PHASE
control at 0"
GATE INPUT
PHASE
control at 90" LEAD
1 43 1 -04
Fig. 1-6. Single cycle output with variable phase.
REV. C JUL '1978

Operating Instructions-FG 501
The phase (start level) of the waveform burst can be
varied +90° by pullingout andturningthe PHASEcontrol
either counterclockwise or clockwise from the 0
(centered)position (see Fig. 1-6). The phaseof theoutput
burst isreferencedtothesineortrianglewaveform 0° start
point.
Output frequency can be varied during the burst
duration by applying a voltage-controlled frequency
(VCF) signal tothe VCF INPUT connector.
Voltage-Controlled Frequency (VCF) Output
Theoutputfrequency of any selected waveformcanbe
swept within a range of 1000:l by applying a 0 to 10 V
signal to the VCF INPUT connector. The polarity of the
VCF input signal determines which direction the output
frequency sweeps from the frequency slet by the
MULTIPLIER selector and FREQUENCY Hz dial; i.e., a
+
,-,
signal sweeps the frequency upward as shown in Fig.
1-7(A), a
- signal sweeps the frequency doiwnward as
shown in Fig. 1-7(B).
Themaximum sweptfrequencyrangeof 1000:1encom-
passes the sensitive uncalibrated range of the FRE-
QUENCY Hz dial, i.e., <.l to 1. Therefore, to ensure that
the frequency does sweep at least a range of 1000:1, it is
recommended that the FREQUENCY Hzdial be set at 10
and a Oto-1OVsignal beappliedtotheVCF
IN1 connector.
Theoutput will thussweep downwardat least 1000:lfrom
a FREQUENCY Hz dial setting of 10 as shown in Fig.
1-7(B). It may be necessary to vary the CAL control to
obtain the full 1000:l swept range or the lowest swept
frequency desired.
SWEPT FREQUENCY
RANGE
(A) Uncalibrated
VCF
INPUT INPUT INPUT
-5
OUTPUT OUTPUT OUTPUT
Fig. 1-7. Swept Frequency rangewith 10 V signals applied to VCF IN connector.
REV. B JUL 1978