background image

15

Subject to change without notice

Very small phase differences with moderately high frequencies 
may yield better results with Lissajous fi gures.

However, in order to get higher precision it is possible to switch 
to higher sensitivities – after accurately positioning at graticule 
centre – thus overdriving the inputs resulting in sharper zero 
crossings. Also, it is possible to use half a period over the full 
10 cm. As the time base is quite accurate increasing the time 
base speed after adjusting for e.g. one period = 10 cm and 
positioning the fi rst crossing on the fi rst graticule line will also 
give better resolution.

Measurement of amplitude modulation

Please note: Use this only in analog mode because in digital 
mode alias displays may void the measurement! For the display 
of low modulation frequencies a slow time base (TIME/DIV) has 
to be selected in order to display one full period of the modu-
lating signal. As the sampling frequency of any digital must be 
reduced at slow time bases it may become too low for a true 
representation.

The momentary amplitude at time t of a hf carrier frequency 
modulated by a sinusoidal low frequency is given by:

u = U

T

 

·

 sin

Ω

t + 0,5 m 

·

 U

T

 

·

 cos (

Ω

 - 

ω

) t - 0,5 m 

·

 U

T

 

·

 cos (

Ω

 - 

ω

) t

where: U

T

  =  amplitude of the unmodulated carrier

 

Ω

 = 

2

π

F = angular carrier frequency

 

ω

 = 

2

π

f = modulation angular frequency

 

=  modulation degree (

v

100%)

In addition to the carrier a lower side band F – f and an upper 
side band F + f will be generated by the modulation.

Picture 1: Amplitudes and frequencies  with AM (m = 50 %) of 
the spectra 

As long as the frequencies involved remain within the scope’s 
bandwidth the amplitude-modulated hf can be displayed. Pre-
ferably the time base is adjusted so that several signal periods 
will be displayed. Triggering is best done from the modulation 
frequency. Sometimes a stable displayed can be achieved by 
twiddling with the time base variable. 

Picture 2: Amplitude modulated hf. F = 1 MHz, f = 1 kHz, 
m = 50 %, U

T

 = 28,3 mV

rms

Set the scope controls as follows in order to display the picture 
2 signal:

CH1 only, 20 mV/cm, AC
TIME/DIV: 0.2 ms/cm
Triggering: NORMAL, AC, internal. 
Use the time base variable or external triggering.

Reading a and b off the screen the modulation degree will 
result:

 

a – b 

a – b

m  =   ——  bzw.  m  =   ——   

·

  100  [%] 

 

a + b 

a + b

a = U

(1 + m)  and  b = U

T

 (1 – m)

When measuring the modulation degree the amplitude and time 
variables can be used without any infl uence on the result.

Triggering and time base

The most important controls and displays for these functions 
are to be found in the shaded TRIGGER area, they are described 
in „Controls and Readout“.-

In YT mode the signal will defl ect the trace vertically while the 
time will defl ect it horizontally, the speed can be selected.
In general periodic voltage signals are displayed with a peri-
odically repeating time base. In order to have a stable display 
successive periods must trigger the time base at exactly the 
same time position of the signal (amplitude and slope). 

STOP

  Pure DC can not trigger the time base, a voltage 

change is necessary.

Triggering may be internal from any of the input signals or 
externally from a time-related signal.

For triggering a minimum signal amplitude is required which 
can be determined with a sine wave signal. With internal trigge-
ring the trigger take-off within the vertical amplifi ers is directly 
following the attenuators. The minimum amplitude is specifi ed 
in mm on the screen. Thus it is not necessary to give a minimum 
voltage for each setting of the attenuator. 

For external triggering the appropriate input connector is used, 
the amplitude necessary there is given in V

pp

. The voltage for 

triggering may be much higher than the minimum, however, it 
should be limited to 20 times the minimum. Please note that 
for good triggering the voltage resp. signal height should be a 
good deal above the minimum. The scope features two trigger 
modes to be described in the following:

Automatic peak triggering (MODE menu)

Consult the chapters MODE 

20

 

>

 AUTO, LEVEL A/B 

19

, FILTER 

21

 and SOURCE 

22

 in ”Controls and Readout“. Using AUTOSET 

this trigger mode will be automatically selected. With DC coup-
ling and with alternate trigger this mode will be left while the 
automatic triggering will remain.

Automatic triggering causes a new time base start after the end 
of the foregoing and after the hold-off time has elapsed even 

          T r i g g e r i n g  a n d  t i m e  b a s e

F – f     

F

     F + f

0,5 m · U

T

0,5 m · U

T

U

T

b

a

m · U

T

U

T

Summary of Contents for CombiScope HM2008

Page 1: ...200 MHz Mixed Signal CombiScope HM2008 Manual English...

Page 2: ...irective des equipements basse tension 73 23 CEE amend e par 93 68 CEE Angewendete harmonisierte Normen Harmonized standards applied Normes harmonis es utilis es Sicherheit Safety S curit EN 61010 1 2...

Page 3: ...ajous gures 14 Measurement of phase differences in dual channel Yt mode 14 Measurement of amplitude modulation 15 Triggering and time base 15 Automatic peak triggering MODE menu 15 Normal trigger mode...

Page 4: ...t voltage Time Base 2ns div 50s div Acquisition modes Single Refresh Average Envelope Roll Peak Detect Front USB Stick Connector for Screenshots USB RS 232 optional IEEE 488 or Ethernet USB Signal dis...

Page 5: ...range 0 250 MHz Coupling DC Level control range 10 10 div Horizontal Deflection Analog Time Base Operating modes A ALT alternating A B B Time base A 20 ns div 0 5 s div 1 2 5 sequence Time base B 20 n...

Page 6: ...rent positions A and B carrying C horizontal operating D and E operating at different angles F handle removal T shipping handle unlocked A A B B C C D D E E T F PUkT PUkT PUk PUk PUk PUk PUk PUk PUkT...

Page 7: ...may be 20 C to 70 C Please note that after exposure to such temperatures or in case of condensation proper time must be allowed until the instrument has reached the permissible temperature resp until...

Page 8: ...V SCALE VAR knob 34 Channel 1 Y de ection coef cient Y variabel and Y scaling setting 17 VOLTS DIV SCALE VAR knob 34 Channel 2 Y de ection coef cient Y variabel and Y scaling setting 18 AUTO MEASURE p...

Page 9: ...selection of PROBE ADJ square wave signal hard ware and software information and details about interface rear side and USB Stick ash drive connector 42 COMPONENT TESTER 2 sockets with 4 mm 47 Connecto...

Page 10: ...st be taken however when charging and discharging a large capacitor DC coupling is preferable with all signals of varying duty cycle otherwise the display will move up and down depending on the duty c...

Page 11: ...ursors may be used for measurement Measurement Adjust the rising portion of the signal to 5 cm Position the rising portion symmetrically to the graticule centre line using both Y and X positioning con...

Page 12: ...e ground connections of probes are especially critical they should be as short as possible and of large size STOP If a probe is to be connected to a BNC connector use a probe tip to BNC adapter If rip...

Page 13: ...mind The oscillosco pe vertical ampli ers are two separate ampli ers and do not constitute a true difference ampli er with as well a high CM rejection as a high permissible CM range Therefore please o...

Page 14: ...and Y signals af ter reading a and b off the screen is possible using the following formulas and a pocket calculator with trigonometric functions This calculation is independent of the signal amplitud...

Page 15: ...ime base variable or external triggering Reading a and b off the screen the modulation degree will result a b a b m bzw m 100 a b a b a UT 1 m and b UT 1 m When measuring the modulation degree the amp...

Page 16: ...ange the slope Positive or negative slope may be selected in auto or normal trigger modes Also a setting both may be selected which will cause a trigger irrespective of the polarity of the next slope...

Page 17: ...Insert a 100 resistor between the center conductor and the BNC connector If possible the coil should be shielded without creating a shorted winding Alternate trigger This mode is selected with SOURCE...

Page 18: ...time for most of the time the digital will not see the signal Also in analog mode the signal itself will be seen on the screen in real time whereas a digital can only show a reconstruction of the sig...

Page 19: ...er COMPONENT PROBE 40 and COMPONENT TESTER 41 The scope has a built in component tester The test object is connected with 4 mm banana plugs In this mode the Y ampli ers and the time base are turned of...

Page 20: ...pend strongly on the kind of FET With depletion type MOSFETs and all JFETs the channel will conduct if prior to testing the gate was connected to the source The Rdson will be shown As this can be very...

Page 21: ...ependent single event recording with Yt display Single Readout display sgl 4 Trigger independent continuous recording menu VERT XY with XY display XY Readout display XY 5 XY display of previously in Y...

Page 22: ...value of the sampling interval 1 sampling interval sampling rate 3 The signal frequency value is related to the highest sine wave signal frequency that can be captured with 10 samples per period realt...

Page 23: ...s shows a straight line in the position of the positive peak value and consequently suggest a positive DC voltage An alias may also take the form of a signal of much lower frequency beat frequency bet...

Page 24: ...rogram for USB connection test RS 232 The RS 232 interface has the usual 9 pole SubD connector Via this bidirectional interface the scope can be controlled remo tely or its settings may be transferred...

Page 25: ...ilable submenus In some modes various pushbuttons or INTENS operations are meaningless and will hence not cause a menu display STOP Please note If a menu is shown some other information dis played in...

Page 26: ...to leave the menu Thereafter only the signal display is activated and the FOCUS TRACE MENU pushbutton will blink as long as the readout is off Pressing the ashing pushbutton calls the Int Knob menu wh...

Page 27: ...hannel mode Yt in the section First time operation and pre settings One period of a sine wave is equal to 2 hence the dis tance between the two long CURSOR lines must be set to one period If the dista...

Page 28: ...will be lost after turn off Mathematics offers 7 1 Equations set Using the INTENS knob 5 sets of formulas can be selected for editing This way 5 user de ned formula sets may be created Each set of fo...

Page 29: ...he display of the former The display will remain on screen until the next acquisition is started by the trigger and causes a new recording This mode is available over the full time base range 50 s cm...

Page 30: ...size is 0 25 s between the samples at a time base setting of 50 s cm The advantage of Peak Detect is that signals are sampled with the highest possible sampling rate to reduce the gap size so that eve...

Page 31: ...RE1 RE1 the signal will be displayed twice on the same spot Associated settings Pressing this function key causes the oscilloscope to take over the settings parameter stored when the signal was store...

Page 32: ...s will remain The digital modes Roll Envelope or Average will be changed to refresh mode AUTOSET will further set the intensity to an average value if it was set too low If a menu was opened it will b...

Page 33: ...control if Yt mode time base mode is present and the CH1 2 CURSOR MA REF ZOOM pushbutton 15 is not lit 14 1 2 Y Position of the FFT display only in digital mode measured with channel 2 Position 2 allo...

Page 34: ...he CH1 menu the de ection coef cient becomes calibrated the CH1 VAR pushbutton 31 does not light any longer and the VOLTS DIV SCALE VAR knob 16 returns to 1 2 5 sequence 16 3 Scaling the FFT display d...

Page 35: ...at V rms the range is from 5mV cm to 20V cm also switched in 1 2 5 sequence Please note that in contrast to Yt and XY mode signal display no peak to peak values but rms values are displayed 18 AUTO ME...

Page 36: ...me base set B trigger to positive or negative slope Thereafter the LEVEL A B control will control the time base B trigger a second trigger point symbol will be shown and marked with B 19 2 FFT mode Th...

Page 37: ...mpli er bandwidth and consequently less trigger signal noise Readout Tr Source Slope AC or DC NR 21 1 2 Slope SLOPE determines whether the rising or falling portion of a signal shall trigger the level...

Page 38: ...5 External In this mode the trigger signal comes from the AUXILIARY INPUT TRIG EXT 38 Readout Tr ext Slope Filter 22 1 6 AC Line The trigger signal is taken from the line mains supply which feeds the...

Page 39: ...ither reference nor mathematic signals are displayed The expanded portion of the signal will be shown on the normal display as an intensi ed sector The length of this sector is dependent upon the sett...

Page 40: ...ave form become digitised and at least show spectrum displays spectra that do not exist in reality If the sampling rate is too low the readout displays ALS if the signal is too high overrange will be...

Page 41: ...nly B The TIME DIV SCA LE VAR knob then only affects time base B By aid of the MAG x10 pushbutton 29 the signal display can be expanded 10 fold reducing the time de ection coef cient by factor 10 30 1...

Page 42: ...sensitivity setting is for AC and is for DC 31 1 1 DC coupling The signal will be directly coupled from the BNC connector via the attenuator to the vertical ampli er The input resistance is 1 M in all...

Page 43: ...DUAL trace alt chop In dual trace mode both channels are turned on and the para meters of both are shown in the readout Between the sensi tivity indications there is an indication whether alternate al...

Page 44: ...It is recommended rst to look at the signals in DUAL mode and to set the sampling rate such that at least one signal period will be displayed Then XY should be selected In XY digital mode both channe...

Page 45: ...he VOLTS DIV SCALE VAR knob 17 returns to 1 2 5 sequence switching and CH2 to calibrated condition 34 INPUT CH1 BNC connector This is the CH1 signal input connector In Yt mode it is a Y input in XY mo...

Page 46: ...accuracy of the FFT calculations in the following averageing process Numbers between 2 and 512 can be chosen by aid of the INTENS 2 knob which are displayed by the readout e g avg 256 The accuracy in...

Page 47: ...ive is connected with the USB Stick connector 43 41 4 1 USB Stick Save Front Panel current oscilloscope parameters The current parameters are saved on the USB ash drive by pressing the function key Sa...

Page 48: ...D 63533 Mainhausen A Rohde Schwarz Company Tel 49 0 61 82 800 0 DQS Certi cation DIN EN ISO 9001 2000 Fax 49 0 61 82 800 100 Reg Nr 071040 QM sales hameg com w w w h a m e g c o m 41 2008 00E1 authori...

Reviews: