Hameg HM8021-4 User manual

1.6 GHz
Universal Counter
HM8021-4
Handbuch / Manual / Manuel / Manual
Deutsch / English / Français / Español
99 Washington Street
Melrose, MA 02176
Phone [phone]
Toll Free 1-800-517-8431
Visit us at www.TestEquipmentDepot.com

Subject to change without notice
14
General information regarding the
CE marking
HAMEG instruments fulfill the regulations of the
EMC directive. The conformity test made by HA-
MEG is based on the actual generic and product
standards. In cases where different limit values
are applicable, HAMEG applies the strictest
standard. For emission the limits for residential,
commercial and light industry are applied. Re-
garding the immunity (susceptibility) the limits
for industrial environment have been used.
The measuring and data lines of the instrument
have much influence on emission and immunity
and therefore on meeting the acceptance limits.
For different applications the lines and/or cables
used may be different. For measurement opera-
tion the following hints and conditions regarding
emission and immunity should be observed:
1. Data cables
For the connection between instruments resp.
their interfaces and external devices, (computer,
printer etc.) sufficiently screened cables must
be used.
Maximum cable length of data lines must not ex-
ceed 3 m. The manual may specify shorter lengths.
If several interface connectors are provided only
one of them may be used at any time.
Basically interconnections must have a double
screening. For IEEE-bus purposes the double
screened cable HZ72 from HAMEG is suitable.
2. Signal cables
Basically test leads for signal interconnection
between test point and instrument should be
as short as possible. Without instruction in the
manual for a shorter length, signal lines must be
less than 3 meters long.
Signal lines must be screened (coaxial cable - RG58/
U). A proper ground connection is required. In com-
bination with signal generators double screened
cables (RG223/U, RG214/U) must be used.
3. Influence on measuring instruments.
In the presence of strong high frequency electric
or magnetic fields, even with careful setup of the
measuring equipment an influence can not be
excluded.
General information regarding the CE marking
The HAMEG Instruments GmbH herewith
declares conformity of the product
Product name Universal Counter
Type: HM8021-4
with: HM8001-2
Options: –
with applicable regulations
EMC Directive 89/336/EEC amended by
91/263/EWG, 92/31/EEC
Low-Voltage Equipment Directive 73/23/EEC
amended by 93/68/EEC
Harmonized standards applied
Safety
EN 61010-1: 2001 / IEC (CEI) 1010-1: 2001
Measuring category I
Degree of pollution: 2
Electromagnetic compatibility
EN 61326-1/A1 :1997 + A1:1998 + A2 :2001/
IEC 61326 :1997 + A1 :1998 + A2 :2001
Radiation: table 4; Class B
Immunity: table A1
EN 61000-3-2/A14
Harmonic current emissions: Class D
EN 61000-3-3
Voltage fluctuations and flicker
Date: 12.05.2004
Signature
Manuel Roth
Manager
Manufacturer HAMEG Instruments GmbH
Industriestraße 6
D-63533 Mainhausen
DECLARATION OF
CONFORMITY

Subject to change without notice 15
Content
This will not cause damage or put the instrument
out of operation. Small deviations of the measu-
ring value (reading) exceeding the instrument‘s
specifications may result from such conditions
in some cases.
HAMEG Instruments GmbH
Deutsch 2
Français 26
Español 38
English
General information regarding
CE-marking 14
Universal Counter HM8021-4 16
Specifications 17
Important hints 18
Safety 18
Used Symbols 18
Operating conditions 18
Warranty and repair 18
Maintenance 19
Operation of the module 19
Control elements of HM8021-4 20
Triggering, measuring and counting 21
Power on test 21
Measuring functions 21
Input triggering 22
Measuring time and resolution 22
Signal inputs 23
Frequency measurement 23
Period measurement 23
Time interval measurement 23
Totalizing (Event counting) 23
External gate 23
Calibration 24

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16
HM8021-4
1.6 GHz Universal Counter
HM8021-4
Frequency range 0 Hz to 1.6 GHz
10 MHz time base with 0.5 ppm stability (TCXO)
Input A:
Input impedance 1 MΩ, maximum sensitivity 20mVrms
Input C:
Input impedance 50 Ω, maximum sensitivity 30mVrms
Time interval resolution up to 10 ps
Offset mode over the entire measurement range
Gate input (in combination with HO801)
Mainframe HM8001-2 required for operation
Option HO85, a high stabi-
lity oscillator with a sta-
bility of ±5x10-9 per day
Option HO801
Mainframe
HM8001-2

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Totalize (manual / external gated)
Range: DC to 20 MHz
Min. pulse duration: 25 ns
LSD: ±1 count
Resolution: LSD
Ext. gate error: 100 ns (in manual mode only)
Time interval (averaged)
LSD: 100 ns to 10 ps
Resolution: 1 or 2 LSD
Offset
Range: covers the entire measurement
range
Gate time
(Gate time cannot be less than 1 period.)
Range: 100 ms – 10 s in 3 steps
External gate time: min. 150 μs
Timebase
Frequency: 10 MHz clock
10 MHz crystal
Accuracy (between 10°C and 40° C): ±5 x 10-7
Aging: ±3 ppm/15 years
General information
Display: 8-digit 7-segment LED display with
7.65mm digit height, sign and
exponent
Power consumption: approx. 7 Watt
Operating temperature: +10°C to +40°C
Max. relative humidity: 0 % – 90%
(without condensation), 5% – 95% RH
Dimensions (W x H x D): 135 x 68 x 228mm
Weight: approx. 0.6 kg
Values without tolerances are meant to be guidelines and
represent characteristics of an average instrument.
Measurement functions
Frequency A/C, Period A; Totalize A;
Pulse width (averaged); Totalize A during ext. gate
Input characteristics (Input A)
Frequency range:
0 – 150 MHz: DC-coupled
10 Hz – 150 MHz: AC-coupled
Sensitivity: (normal triggering)
DC – 80 MHz: 20 mVrms (sine wave)
80 mV (pulse)
80 MHz – 150 MHz: 60 mVrms (sine wave)
20 Hz-80MHz (auto trig.) 50 mVrms (sine wave)
Minimum pulse width: 5ns
Input noise: 100 μV (typ.)
Coupling: AC or DC (switchable)
Input impedance: 1 MΩII 40 pF
Attenuator: x 1, x 20 (switchable)
Max. input voltage:
0 to 440 Hz: 400 V (DC + ACpeak)
1 MHz: decreasing to 8 Vrms
Input characteristics (Input C)
Frequency range: 100 MHz – 1.6 GHz
Sensitivity:
to 1.3 GHz: 30 mV (typ. 20 mV)
to 1.6 GHz: 100 mV (typ. 80 mV)
Input impedance: 50 Ωnominal
Coupling: AC
Max. input voltage: 5 V (DC + ACpeak)
Input characteristics (external gate)
Input impedance: 4.7 kΩ
Max. input voltage: ±30 V
High/low level: › 2 V/‹ 0.5 V
Min. pulse duration: 50 ns
Min. effective gate time: 150 μs
Frequency measurement (Input A)
LSD: (2.5x10-7s x freq.)/measurement
time
Resolution: ±1 or 2 LSD
Period duration measurement
Range: 10000 sec to 66.6 ns
LSD: (2.5 x 10-7s x period)/measurement
time
Resolution: ±1 or 2 LSD
Specifications
TECHNISCHE DATEN
Referenztemperatur: 23°C ±2 °C
TECHNISCHE DATEN
Referenztemperatur: 23°C ±2 °C
1.6 GHZ Universal Counter
SPECIFICATIONS
Valid at 23degrees C after a 30 minute warm-up
Included in delivery:
Universal Counter HM8021-4, Operator’s
Manual
Optional accessories: HZ33/HZ34 BNC Test
Cable, HZ24 Attenuators, HZ20
BNC banana adapter, HO85 OCXO, HZ10 Silicone
test leads

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18
TRIPLE POWER SUPPLYHM 8040-3
HAMEG
VOLTAGE CURRENT CURRENTVOLTAGE
FUSE
ON/OFF
FUSE
ON/OFF
PUSHLONG
OUTPUT
Important hints
Important hints
The operator is requested to carefully read the
following instructions and those of the mainfra-
me HM8001-2, to avoid
any operating errors and
mistakes and in order to
become aquainted with the
module.
After unpacking the module, check for any me-
chanical damage or loose parts inside. Should
there be any transportation damage, inform the
supplier immediately and do not put the module
into operation. This plug-in module is primarily
intended for use in conjunction with the Mainfra-
me HM8001-2. When incorporating it into other
systems, the module should only be operated with
the specified supply voltages.
Safety
This instrument has been designed and tested in
accordance with IEC Publication 1010-1, Safety
requirements for electrical equipment for measu-
rement, control, and laboratory use. It corres-
ponds as well to the the CENELEC regulations EN
61010-1. All case and chassis parts are connected
to the safety earth conductor. Corresponding to
Safety Class 1 regulations (three-conductor AC
power cable). Without an isolating transformer,
the instrument's power cable must be plugged into
an approved three-contact electrical outlet, which
meets International Electrotechnical Commission
(IEC) safety standards.
Warning!
Any interruption of the protective conductor
inside or outside the instrument or discon-
nection of the protective earth terminal is
likely to render the instrument dangerous.
Intentional interruption is prohibited.
The istrument must be disconnected and secured
against unintentional operation if there is any sug-
gestion that safe operation is not possible.
This may occur:
– if the instrument shows visible damage,
– if the instrument has loose parts.
– if the instrument does not function,
– after long storage under unfavourable circ-
umstances (e.g. outdoors or in moist environ-
ments),
– after excessive transportation stress (e.g. in
poor packaging).
When removing or replacing the metal case, the
instrument must be completely disconnected
from the mains supply. If any measurement or
calibration procedures are necessary on the
opened-up instrument, these must only be carried
out by qualified personnel acquainted with the
danger involved.
Symbols marked on equipment
ATTENTION refer to manual.
DANGER High voltage.
Protective ground (earth) terminal.
Operating conditions
The ambient temperature range during operation
should be between +10°C and +40 °C and should
not exceed –40 °C or +70 °C during transport or
storage. The operational position is optional, how-
ever, the ventilation holes on the HM8001-2 and on
the plug-in modules must not be obstructed.
Warranty and Repair
HAMEG instruments are subjected to a strict qua-
lity control. Prior to leaving the factory, each ins-
trument is burnt-in for 10 hours. By intermittent
operation during this period almost all defects are
detected. Following the burn-in, each instrument
is tested for function and quality, the specifications
are checked in all operating modes; the test gear
is calibrated to national standards.

Important hints
The warranty standards applicable are those of
the country in which the instrument was sold.
Reclamations should be directed to the dealer.
Only valid in EU countries
In order to speed reclamations customers in EU
countries may also contact HAMEG directly. Also,
after the warranty expired, the HAMEG service will
be at your disposal for any repairs.
Return material authorization (RMA):
Prior to returning an instrument to HAMEG ask
for a RMA number either by internet (http://www.
hameg.com) or fax. If you do not have an original
shipping carton, you may obtain one by calling
the HAMEG sales dept ([phone]) or by
sending an email to [e-mail].
Maintenance
The most important characteristics of the instru-
ments should be periodically checked according to
the instructions provided in the sections “Opera-
tional check and “Alignment procedcure. To obtain
the normal operating temperature, the mainframe
with inserted module should be turned on at least
60 minutes before starting the test. The specified
alignment procedure should be strictly observed.
When removing the case detach mains/line cord
and any other connected cables from case of the
mainframe HM8001-2. Remove both screws on
rear panel and, holding case firmly in place, pull
chassis forward out of case. When later replacing
the case, care should be taken to ensure that
it properly fits under the edges of the front and
rear frames. After removal of the two screws at
the rear of the module, both chassis covers can
be lifted. When reclosing the module, care should
be taken that the guides engage correctly with the
front chassis.
Operation of the module
Provided that all hints given in the operating
instructions of the HM8001-2 Mainframe were
followed especially for the selection of the cor-
rect mains voltage start of operation consists
practically of inserting the module into the right
or left opening of the mainframe. The following
pre-cautions should be observed:
Before exchanging the module, the mainframe
must be switched off. A small circle (o) is now
revealed on the red power button in the front
centre of the mainframe.
If the BNC sockets at the rear panel of the
HM8001-2 unit were in use before, the BNC cables
should be disconnected from the basic unit for
safety reasons. Slide in the new module until the
end position is reached.
Before being locked in place, the cabinet of the
instrument is not connected to the protective earth
terminal (banana plug above the mainframe mul-
tipoint connector). In this case, no test signal must
be applied to the input terminals of the module.
Generally, the HM8001-2 set must be turned on
and in full operating condition, before applying any
test signal. If a failure of the measuring equipment
is detected, no further measurements should
be performed. Before switching off the unit or
exchanging a module, the instrument must be
disconnected from the test circuit.
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
FAX [phone] - TestEquipmentDepot.com

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20
Control elements
Control elements
OF (LED)
This LED is lit when an overflow ocurs. This
depends on the selected gate time and on the
frequency of the signal applied.
GT (Gate Open; LED)
The gate indicator is lit when the gate is open
for measurements. This time equals the pre-
selected gate time and a synchronization time.
The gate cannot be open for a time smaller
than 1 period of a signal.
Gate Time (pushbuttons + LEDs)
The gate time is selectable in steps of 0.1s, 1s,
10s.
EXT. (LED)
In the GATE EXTERNAL position, the counter
will expect an external control signal, and will
not measure until such a signal is supplied.
Display Hold (pushbutton + LED)
Depressing the DISPLAY HOLD pushbutton
sets the display time to infinity and freezes
the last measurement result. A new measure-
ment can be initiated using the reset pushbut-
ton. Measuring will restart when Display Hold
is switched off. Display Hold starts and stops
counting in the TOTALIZE function mode.
Function indicators
LEDs (Refer to “Measuring functions”)
Function (pushbuttons)
The “left” and “right” pushbuttons select the
desired function. The appropriate LED is lit
when a function is selected. The default value
when switching power on is Frequency A.
OFFSET (pushbutton + LED)
The displayed value becomes the reference
value. (Not available with the TOTALIZE func-
tion).
RESET (pushbutton + LED)
Stops a measurement and clears the display
in normal measurement mode. When de-
pressing the button in DISPLAY HOLD MODE
the counter performs a single measurement
(one shot) on release of the button. When the
OFFSET MODE is activated, depressing RESET
shows the reference value (which is the actual
offset). Reset is active as long as the button is
depressed.
INPUT C (BNC-connector)
Frequency range: 100MHz to 1.6GHz.
Input impedance 50Ω.
Attention! Do not apply more than 5V (DC+AC
peak) to this input terminal.
DC (pushbutton)
Selection of AC or DC coupling of the signal

Subject to change without notice 21
Functions
input A. The bandwidth for low frequencies
is as low as 10Hz (3dB) when the input is AC
coupled. (Input C has a fixed AC coupling).
1:20 (pushbutton)
Selection of input signal attenuation. Pressing
this button attenuates the input signal by 26dB
before it is applied to the input amplifier.
Auto Trigger (AC) (pushbutton)
With Auto Trigger active the counter triggers
in the middle of the input signal. Auto Trigger
always uses AC-coupling. (AC = pushbutton
depressed).
INPUT A (BNC connector)
Signal input with a sensitivity of 20mVrms up to
80MHz and 60mVrms up to 150 MHz. The input
is protected against overvoltage up to 400V
(DC + ACpeak).
Input impedance: 1MΩ II 40pF.
TRIGGER LEVEL (adjusting knob)
Continuously adjustment of trigger level.
TRIGGER (LED)
3 State trigger indicator. The LED flashes when
triggering is correct. The LED lights when the
trigger level is above the input signal level, it
is not activated when the trigger level is below
the input signal level.
8 digit display
(7 segment LEDs, 7.65 mm high)
for the measuring result (8 digit max. + expo-
nent).
Hz (LED): Indicates the measurement of a
frequency.
Sec (LED): Indicates the measurement of
time.
HM 8001-2:
External Gate Input (BNC connector)
Allows the measurement of the input signal,
controlled by an external source.
Triggering, measuring
and counting
Power-on test
A practical test of the correct operation of the
HM8021-4 is run automatically at power on. As
soon as power is applied, the display shows type
and version of the actual instrument and the GATE
indicator appears, LEDs are lit and the Eprom and
all functions of the counter are tested. The test
runs for about 2 seconds. If an error is detected
it is indicated by an ”I” at the leading digit and
followed by the number of the test that failed.
I 1 microprocessor RAM error
I 2 program ROM error
I 3 counting chain error
When the tests are completed satisfactorily, the
counter sets the display to zero and selects the
default measuring function A.
Measuring functions
FA/FC: Sets the instrument to measure the
frequency of the signal connected to
input A/C.
TOT.: The counter will totalize events
(pulses or cycles) on input A.
Measurement stops and display
freezes as soon as the input signal
is removed or DISPLAY HOLD is
depressed. Depressing RESETcluring
totalizing clearsthe display and starts
a new measurement when releasing
the button. Reset is active as long as
the switch is depressed. Totalizing
A during External Gate is performed
applying a TTL signal to the Ext. Gate
input.
PA: Sets the counter to measure the peri-
od duration of the signal connected to
input A.
TI : Sets the counter to measure the
(AVG) average pulsewidth between positive
slope and the negative slope of an
input signal at input A.

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22
Operational check
Input Triggering
As the input signal can have very different wave-
forms, it is necessary to shape the signals so
that the counting circuits can handle the signals.
The HM8021-4 offers a variaty of signal shaping
possibilities to improve triggering, such as AC/
DC coupling and two trigger level ranges (–2...
2V, –40...+40V). The trigger level can be set in
one of two ways: either by Autotrigger or with the
trigger level potentiometer. In Autotrigger mode
the counter automatically sets the triggering to
the 50% level of the input signal. When this mode
is selected AC coupling is necessary. When the
trigger level control has been set in the manual
trigger mode, the functioning of the trigger circuit
can easily be checked on the trigger indicator. The
LED shows the state of triggering.
LED on: the signal is above the trigger level
LED off: the signal is below the trigger level
LED
blinking: the signal is crossing the hysteresis
band, correct triggering.
For reliable triggering the trigger level should,
in always most cases, be at 50% of the signal’s
peak-to-peak voltage.
Selecting the correct attenuation is important to
obtain the best results from your instrument. If
the attenuation is too high, the measurement will
be affected by the noise of the input comparator.
This results in an unstable display. With an input
signal too great, the input stage may saturate
and thus producing overshoots which result in a
display which is twice too high e.g. at frequency
measurements. Always try to set the control to
AC-coupling and use as much attenuation as pos-
sible for frequency measurements and DC-coup-
ling with no attenuation for time measurements.
In many cases it is vital to have a good impedance
matching to avoid reflections which might make
the trigger level setting very difficult. Always use
a 50 Ωtermination in 50 Ωsystems. The C-input
facilitates no input conditioning controls and
needs no trigger level setting. The input signal is
triggered from 50mV up to the maximum input
voltage of 5V. The input frequency for the C-input
must always be in the range from 100 MHz to
1000 MHz. For frequencies lower than 100MHz the
measurement result may be incorrect.
Measuring time and resolution
The measuring time can be varied in 3 steps
between 100ms and 10sec. The gate time may be
modified during a measurement. In the recipro-
cal mode (at all frequencies with HM8021-4), the
counter totalizes the input cycles until the set
measuring time has elapsed and the synchro-
nization conditions are met. Hence, the effective
measuring time (also called gate time) is longer
than the set measurement time. The measure-
ment in the HM8021-4 is always synchronized to
the input signal. This is called the input synchro-
nized or reciprocal method.
In this mode, both the opening and closing of the
main gate are synchronized with the input signal,
so that only completed input cycles are counted.
This means that a ±1 input cycle error is avoided.
During the gate time, the counter totalizes the
number of clock cycles. When the preselected gate
time is over, the counter waits for the next active
transition of the input signal to stop counting. If
the recurrence of this signal is low, e.g. with long
period times, the stop synchronization time may
be long compared to the preset gate time. In that
case the effective gate time may be very different
from the preset value (if the signal was removed
during measurement, this time becomes infinite
and the measurement finishes never). The reso-
lution in the input synchronized mode is caused
by trunctation of the clock pulses, which results
in +1clock pulse error (100ns). The resolution
of the measurement thus only depends on the
measurement time. For example, the resolution
for 1s measuring time is 10-7, independent of input
frequency. In conventional counters the gate time
is synchronized with the clock signal. The first
and last input cycle can therefore be truncated,
causing a ±1 cycle error. This resuits in a good
resolution for high frequency measurements, but
a poor resolution for low frequency measurements
(±1: frequency, for 1sec. measuring time).

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Alignment procedure
Signal inputs
The front panel of the HM8021-4 has two BNC
input sockets. One (Input A) with an impedance of
1MΩII 40pF. As the frequency measuring range
of the HM8021-4 unit reaches up to 1GHz, this
module offers also an input (C) for frequency
measurements from 100MHz up to 1 GHz. It is
also provided as a BNC socket and has an impe-
dance of 50Ω.
Caution!
Particular care should be taken, when applying
signal voltages to the 1 GHz input of the HM8021-4
unit. A maximum voltage of 5 V (DC+ACpeak) may
be applied to the input C (see ”Specifications”).
Any input voltage exceeding this value will dest-
roy the input stage of the frequency counter!
Frequency measurement
Counters are used for both, frequency and time
interval measurements. However, frequency and
time interval measurements have contradictory
requirements in respect of correct triggering. For
frequency measurements, too high a sensitivity
means that the counter is too sensitive to noise.
Therefore do not use higher sensitivity than needed
for correct triggering. Signals which are superim-
posed on a DC voltage, must be separated via
an input coupling capacitor (i.e. AC-coupling, DC
pushbutton released). The advantages of AC coup-
ling are: no DC-drift and good protection against
DC overload. AC-coupling however, gives a drop
in sensitivity for very low frequencies. The signal
frequency to be measured is applied to one of the
inputs, and the corresponding function is selected.
The trigger point is adjusted by use of the TRIGGER
knob , so that a stable value is displayed. This
stability is obtained, when the trigger signal dis-
play LED flashes (see ”Input triggering”). Now the
test frequency can be read on the 8-digit display.
The obtained resolution depends on the gate time
and can be selected in 3 steps with the GATE TIME
pushbutton switch . When the measurement
range is exceeded, the OVERFLOW LED is light
up. A reliable indication is no longer ensured under
these circumstances. The maximum resolution of
0.1 Hz is obtained with a gate time of 10sec.
Period measurement
For measurement of the period duration, the re-
ciprocal value of the frequency T=1/f is measured
in seconds. The signal is applied as for frequency
measurement.
Time interval measurement
(Pulsewidth)
In TI mode, the time (e.g. number of 100ns clock
pulses) is measured between the positive slope
and the negative slope of an event at channel
A. (Corresponding for negative pulses in TI
mode). In single source time measurements (e.g.
Pulse width) the resolution of the measurement
is one clock pulse (100ns). By using the time in-
terval average technique, which means multiple
measurements of a repetitive signal, the measu-
ring accuracy and resolution are greatly improved.
Compared to single time interval measurements,
the basic 100ns resolution is improved by a factor
of √N, where N is the number of time intervals
being averaged during the measuring time. Note
that the input signal must be repetitive and must
not have a phase relation with the reference fre-
quency. For time interval measurements, too low a
sensitivity means that different signal slopes at the
positive and negative edge cause different delays
between the trigger level crossing and the trigger
point, resulting in incorrect measurements. The
highest possible sensitivity which does not over-
load the input stage, is the ideal. DC-coupling,
attenuation and a continuously variable setting
of the trigger level is necessary for setting the
trigger level at any required point of the input
signal, independent of waveform and duty factor.
Autotriggering requiring AC-coupling is also
possible. The display resolution changes with the
number of measurements taken from the signal.
At single pulse measurements the resolution is
100ns, whereas the resolution may be as small
as 10ps, depending directly on the measurement
time set with the gate switch and the repetition
rate of the input signal.
Totalizing (Event counting)
The kind of signal input is similar as for frequency
measurement. The counting starts at once. Reset
and restart counting is activating by pushing the
knob RESET.
External gate (back of mainframe)
The external gate function allows full control of
the start and stop of the measurement. When Ext.
(gate) is selected and the control input signal

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24
Calibration
is low, the counter makes all necessary prepa-
rations for a measurement. With the high level
of the gate signal, measurement starts when the
input signal triggers after a synchronization delay.
Measurement stops on the first trigger after the
gate signal changes from high to low. The external
gate overrides the set measurement time. The
external gate signal must be in the range 100ns
... 10sec. but the effective gate time will never be
smaller than 150 μs.
External gate is selected by means of the pushbut-
ton and indicated by means of LED. External
gate can be used in all functions.
Example applications are multiple burst fre-
quencies and masked time intervals. Note that
if RF bursts are to be measured using frequency
C, the burst should contain at least 128 cycles of
the f requency to be measured. External gating is
active according to the level applied to the input
(rear side of mainframe).
Calibration
Crystal oscillators are subject to natural aging
during operation, which leads to deviations from
their basic accuracy. Therefore they should be
re-aligned at least twice peryear to ensure the
accuracy indicated in the specification.
Caution!
The time base of the HM8021-4 unit should only
be realigned, if a high-precision frequency stan-
dard is available.
If recallibration is necessary it is carried out as
follows:
1) Select function FA (Frequ.A), OFFSET and
DISPLAY HOLD should be in OFF position.
2) Apply a frequency standard of 1, 5 or 10MHz
to input A and adjust channel A trigger setting
for a stable reading.
3) Depress RESET and then GATE TIME
for approx. 5secs.
4) The display shows ”A...O” during the push
buttons are depressed.
5) When the switches are released the display
shows the date of the last recalibration (DD-
MM-YY or 00-00-00).
6) You may leave calibration mode by depressing
RESET T. In this case no changes are made and
the unit is working in normal mode.
7) If you want to change the date of the last ca-
libration youshouidproceedfromste 5:
Using the key §or ¨(left or right function shift
keys) you can choose the digit that has to be
changed (not flashing). The different digits are
changed by pushing down the GATE TIME
key several times. When the last digit is cor-
rected (now the last digit should light brightly
e.g. 20-02-89) you can leave the calibration
procedure (continue with step 7a) or frequency
calibration can be performed (continue with
step 7b).
7a) If you only want to store the date of the last
calibration without changing the timebase
calibration, there should not be any signal at
the input A during the following steps. After
depressing the right function key ¨”A...” will
be indicated in the display after a few seconds.
If you now depress the reset button you are
again in the normal mode.
7b) If there is a standard frequencyof 1, 5 or 10MHz
at the input A, depress the right function key
¨. A few seconds later the display shows
following informations:
A...if the standard frequency applied is not
accepted
A... 1 6 if the counter has recognized a
1 MHz standard

Subject to change without notice 25
Calibration
A... 5 6 if the counter has recognized a
5MHz standard
A...10 6 if the counter has recognized a
10MHz standard
During the following 45 seconds the signal is
measured and the HM8021-4 is recalibrated.
Finally the new calibrated unit automatically
switches back to normal mode.
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