Download Basic RF Technic and Laboratory Manual

Basic RF Technic and Laboratory Manual
Dr. Haim Matzner&Shimshon Levy
April 2002
2
CONTENTS
I
Experiment-4 Power Meter and Power Measurement
5
1 Introduction
1.1 Prelab Exercise . . . . . . . . . . . . . . . . . . .
1.2 Background Theory . . . . . . . . . . . . . . . . .
1.3 dB and dBm Terminology . . . . . . . . . . . . .
1.4 Fundamentals of RF Power Measurement . . . . .
1.5 Microwave Power Meter -HP-E4418 . . . . . . . .
1.5.1 Theory of Operation . . . . . . . . . . . .
1.6 Types of Power Measurements . . . . . . . . . . .
1.7 Average and Instantenous Power . . . . . . . . .
1.8 Power of Modulated Sinusoidal Signal . . . . . . .
1.9 Pulse Power . . . . . . . . . . . . . . . . . . . . .
1.10 Power Sensing Method . . . . . . . . . . . . . . .
1.10.1 Thermocouple as a sensor of Power meter.
1.10.2 Diode as a Sensor of Power Meter . . . . .
1.10.3 Directional Power Sensor . . . . . . . . . .
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14
16
2 Experiment Procedure
2.1 Required Equipment . . . . . . . . . . .
2.2 Turning On the Power Meter . . . . . .
2.3 Front Panel Tour . . . . . . . . . . . . .
2.4 Power Meter Operation . . . . . . . . . .
2.4.1 Zeroing the Power Meter . . . . .
2.4.2 Calibrating the Power Meter . . .
2.5 Average Power . . . . . . . . . . . . . .
2.6 Power of a Modulated Sinusoidal Signal
2.7 Pulse Power . . . . . . . . . . . . . . . .
2.8 Diode Detector . . . . . . . . . . . . . .
2.9 Final Report . . . . . . . . . . . . . . . .
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2.10 Appendix-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10.1 To phase lock two function generator. . . . . . . . . . . . . . .
2.10.2 Setting a zero phase reference at the end of the cable. . . . . .
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4
CONTENTS
Part I
Experiment-4 Power Meter and
Power Measurement
5
Chapter 1
INTRODUCTION
1.1
Prelab Exercise
1. Define average power, Instantaneous power, PEP, thermocouple principle, square
law region of diode.
2. Describe how you intend to measure incident and reflected power using
directional coupler.
1.2
Background Theory
At low frequencies, the strength of the signal is calculated by measuring the voltage or
current. Voltage and current are related by Ohm’s law (current= voltage÷impedance),
and power defined as the product of voltage and current. At microwave frequencies
the equivalents to voltage is electric field, and magnetic field to current. It is not an
easy task to measure accurately magnetic and electric fields. Power is the quantity
that is measured and the magnetic and electric fields are derived from the measured
power. Power is the amplitude of the electromagnetic wave, and is measured in units
of watts, which related to mechanics units as watt (W ) = 1 joule/sec. At microwave
frequencies, the reference level of power is not 1 W , but 1 mW . The reason is that
a milliwatts of power is enough to operate microwave devices and components, and
even wireless products. Techniques for power measurements depend on frequency.
Below 100kHz, voltage and current are practically measured. At frequencies of tens
hundreds of MHz, power measurement is more accurate then the power calculated by
measuring voltage and current. Above 1GHz, power measurement is dominant and
current and voltage measurements are not practical.
1.3
dB and dBm Terminology
If we look at table one, we see that all the zeroes, before the decimal point for
high powers ( more than 1watt), and the zeroes for low powers make the calculation
cumbersome. For convenience and the cases we perform relative power measurement,
for example, to compare the output power coming out of amplifier, relative to that
going into it. the dB system of units is used and expressed as :
8
Introduction
P
)
(1.1)
Pref
The dB number system can also be used to express absolute value of microwave
power as dBm and defined as:
P [dB] = 10 log10 (
P
)
1mW
Watts
dBm designation
1,000,000
90
1 megawatt
1,000
50
1 kilowatt
1
30
1 watt
0.001
0
1 milliwatt
0.000,001
-30
1 microwatt
0.000,000,001
-60
1 nanowatt
0.000,000,000,001
-90
1 picowatt
0.000,000,000,000,001 -120 1 femtowatt
Table-1 Prefix used to specify microwave power
P [dBm] = 10 log10 (
1.4
(1.2)
Fundamentals of RF Power Measurement
The measurement of power in RF and microwave applications has the same significance as voltage measurements in electrical engineering. Power meters are used
for a wide variety of measurement tasks. In comparison with spectrum or network
analyzers, they are relatively cheap and unsophisticated instruments.
The development of carrier-based telecommunications at the beginning of this
century derived a parallel development in the field of power measurements. The majority of methods were based on converting electrical energy into heat(Thermistor
and thermocouple devices). For a long time, this was the only way of making accurate measurements at practically any frequency. In the meantime, direct voltage
and current measurements can be made up into the GHz range assuming matched
system without having to convert electrical energy into heat. Nevertheless, the intensity of RF and microwave signals is still given in terms of power. Apart from the
high accuracy of thermal power meters, there are other important reasons for using
power. Any signal transmission by waves, for example sound propagation, involves
the transfer of energy. Only the rate of energy flow, power, is an absolute measure of
wave intensity. In the RF and microwave ranges, the wave properties of the electromagnetic field play an important role because the dimensions of the lines used are of
the same order of magnitude as the wavelength used. This fact has to be taken into
account when the quantity to be measured . Voltage and current are less appropriate because they depend on the physical characteristics of the transmission medium
(dimensions, dielectric constant, permeability) and field strength. Consider, for example, two matched coaxial cables with characteristic impedance of 50Ω and 75Ω.
Microwave Power Meter -HP-E4418
9
Diode Sensor
RF
Input
Power Meter
Matching
Network
Temperature
Sensor
BPF
EE
PROM
Calibrator
Signal
cocditioni
ng
ADC
Chopper
driver
DSP
Bus
Display
Micro
Processor
Figure 1 Block diagram of Power Meter with Diode Sensor
For the same transmitted power, the voltage and current for the two impedance differ
by a factor of 1.22. here are further reasons for selecting power as the quantity to be
measured. There is no direct way of measuring voltage and current in waveguides,
and when standing waves occur, there are large measurement errors.
1.5
Microwave Power Meter -HP-E4418
1.5.1 Theory of Operation
Digital signal processing and microwave semiconductor technology have now advanced
to the point where dramatically-improved performance and capabilities are available
for diode power sensing and metering power sensors are now capable of measuring
over a wide dynamic - 70 to +20 dBm, range of 90 dB . This permits the new sensors
to be used for CW applications which previously required two sensors.
The new HP ECP-E18A power sensor features a frequency range 10 MHz to
18 GHz. A simplified block-diagram of the sensor is shown in Figure-1 . The front
end construction is combines the matching input pad ( low value Attenuator), diodes,
FET choppers, integrated RF filter capacitors, a driving pre-amplifier. All of those
components operate at such low levels that it was necessary to integrate them into
a single thermal space on a surface-mount-technology PC board. To achieve the
expanded dynamic range of 90-dB, the sensor/meter architecture depends on a data
compensation algorithm, which is calibrated and stored in an individual EEPROM in
each sensor. The data algorithm stores information of three parameters, input power
level versus frequency versus temperature for the range 10 MHz to 18 and - 70 to +20
dBm and 0 to 55 ◦ C. At the time of sensor power-up, the power meter interrogates the
attached sensor, using an industry-standard serial bus format, and in turn, receives
the upload of sensor calibration data. An internal temperature sensor supplies the
diode’s temperature data for the temperature-compensation algorithm in the power
meter. The new sensor store cal-factor tables for two different input power levels to
10
Introduction
Average Power
Amplitude
θ
Voltage
Current
Power
t
Amplitude of sinusoidal power (solid line), voltage (dashed line), current (dashdotted line), and average power (dotted line) as function of time. θ is the phase
difference between current and voltage.
Figure 2 Average and Instantenous power
improve accuracy of the correction routines. Figure -1 shows a simplified schematic
of the HP EPM-4418A meter. The pre-amplified sensor output signal receives some
early amplification, followed by some signal conditioning and filtering. The signal is
then applied to a dual ADC. A serial output from the ADC takes the sampled signals
to the digital signal processor, which is controlled by the main microprocessor. A
differential drive signal, synchronized to the ADC sampling clock, is output to the
sensor for its chopping function.The ADC provides a 20-bit data stream to the digital
signal processor, which is under control of the main microprocessor. Even the synchronous detection is performed by the ADC and DSP rather than use of a traditional
synchronous detector. Experiment-3 Power Meter and Power Measurement
1.6
Types of Power Measurements
The main types of power measurements are: average power, pulse power and peak
envelope power. The first is suitable for energy transfer considerations, the second
type deals with square shape power pulses as function of time, and the last with a
more complicated shapes of power as function of time. The pulse power measurement
gives us also peak power values, which is an important information in many cases.
In order to have a peak envelope power measurement, a relatively great number of
single power measurements is performed, such that the needed details of the power
as function of time are seen.
1.7
Average and Instantenous Power
Power is usually defined as the rate of transfer or absorption of energy per unit time.
The power transmitted across a system is the product of the instantaneous values of
current and voltage at that system(see Fig-2).
Power of Modulated Sinusoidal Signal
11
Let the Voltage be
v(t) = Vm cos(wt + θv )
and the current
i(t) = Im cos(wt + θi )
Then the power will be
p(t) = v(t)i(t) = Vm cos(wt + θv )Im cos(wt + θi )
we get
by using the trigonometric identity cos θ1 cos θ2 = 12 [cos(θ1 − θ2 ) + cos(θ1 + θ2 )]
we get
Vm Im
Vm Im
cos(θv − θi ) +
cos(2wt + θv + θi )
2
2
by using the trigonometric identity cos(θ1 + θ2 ) = cos θ1 cos θ2 − sin θ1 sin θ2
p(t) =
Vm Im
(1.3)
cos(θv − θi ) +
2
Vm Im
Vm Im
+
cos(θv + θi ) cos 2wt −
sin(θv + θi ) sin 2wt
2
2
the following points can be made concerning equation-6.3 and Fig.-2
1. The average value of the power (or the DC component) is given by Vm2Im cos(θv −
θi ) and has maximum when the phase difference between current and voltage equal
zero.
2. The frequency of the instantenous power is twice the frequency of voltage
or current.
3. If the phase difference between voltage and current is +π/2, the circuit
is purely inductive and the average power will be zero ,power will oscillate between
source and inductor.
4. If the phase difference between voltage and current is -π/2, the circuit is
purely cacitive and the average power will be zero ,power will oscillate between source
and capacitor.
p(t) =
1.8
Power of Modulated Sinusoidal Signal
When modulated sinusoidal signals are applied, other definitions of power are more
appropriate to the system (Fig-3). The average of P over the modulation period is
called the average power P avg. This is what a thermal power meter would indicate.
The power averaged over one period of a carrier is referred to as the envelope
power P e(t). It varies in time with the modulation frequency. The maximum envelope
power is referred to as the peak envelope power or P EP . PEP is an important
parameter for specifying transmitters. P EP and the envelope power can only be
measured with peak or envelope power meters, which use fast diode sensors.
12
Introduction
V
t
0
AM voltage signal
p
PEP
Instantaneous Power
Envelope Power
Average Power
0
t
Figure 3 PEP and instantaneous power of Am Signal
1.9
Pulse Power
power of the pulse is averaged over the pulse width τ , Pulse width τ is considered
to be the time between the 50 percent rise-time and fall time amplitude points ( see
Fig-4). Pulse power is defined by
1
P =
τ
Zτ
v(t)i(t)dt
0
By definition, pulse power is averages out any aberrations in the pulse envelope such
as overshoot or undershoot ringing.
The definition of pulse power has been extended since the early days of microwave to be:
Pavg
Pp =
Duty Cycle
where duty cycle is the pulse width times the repetition frequency. This extended
definition, allows calculation of pulse power from an average power measurement and
the duty cycle. For microwave systems which are designed for a fixed duty cycle,
peak power is often calculated by use of the duty cycle calculation along with an
average power sensor. One reason is that the instrumentation is less expensive, and
in a technical sense, the averaging technique integrates all the pulse imperfections
into the average. For microwave systems which are designed for a fixed duty cycle,
peak power is often calculated by use of the duty cycle calculation along with an
average power sensor.
Power Sensing Method
13
PRI=1/PRF
Power
pulse width τ
Duty cycle=PRF. τ
Pulse top
amplitude
Average Power
PRI
Time
Figure 4 Common Pulse Parameters
* Thermocouple
* Diode
* Directional- Substituted DC
Coupler
or AC Signal
RF
input
power
Meter
Sensing elements
Figure 5 Four type of power sensing methods
1.10
Power Sensing Method
Most of power sensors convert high frequency power to a DC or low frequency signal
that the power meter can then measure and relate to a certain RF power level.
The Four main types of sensors are thermistors, thermocouples, diode detectors, and
directional coupler (see Fig-5). Each power sensor has it’s benefits and limitations.
We will briefly go into the theory of each type.
1.10.1 Thermocouple as a sensor of Power meter.
Thermocouple sensors are based on the fact that a different metals generates a voltage due to temperature differences between a hot and a cold junction. If the two
metals are put together in a closed circuit, current will flow due to the difference in
the voltages. If the loop remains closed, current will flow as long as the two junctions remain at different temperatures. In a thermocouple, the loop is broken and
a sensitive DC voltmeter is inserted to measure the net thermoelectric voltage (see
Fig-6). The measuring voltage can be related to a temperature change due to RF
power incident upon the thermocouple element.
14
Introduction
metal-1
Hot-junction
Vdc
Cold junction
metal-2
Figure 6 Thermocouple principle
Since the voltage produced in a thermocouple is very low, it is possible to
connect several junction in series in order to yield larger thermoelectric voltage. The
two main reasons for wide using thermocouple technology are: Thermocouple exhibit wider dynamic range than thermistor technology, and they feature an inherent
square-law detection characteristic proportional to DC . Since thermocouples, like
thermistors with a self-balancing bridge, always respond to the true power of a signal, they are ideal for all types of signal formats from CW to complex modulations.
Thermocouple make usable power measurements down to -30 dBm, and have lower
measurement uncertainty due to a lower SWR.
1.10.2 Diode as a Sensor of Power Meter
Rectifying diodes have long been used as detectors and for relative power measurements at microwave frequencies. Diodes convert high frequency energy to DC by
using rectification properties, inherent to their non-linear current-voltage (i-v) characteristics. The advantage of the diode is that they can be used for measurement of
extremely low powers. Refer to Fig-8 and Fig.-9 You can see that their square-law
region begin from -70 to -30 dBm.
Mathematically, a detection diode obeys the diode detection
qv
I = Is (e kt − 1) = Is (eαv − 1)
q
α =
kt
(1.4)
where Is is the saturation current (about 10 µA), q is the electron charge ,
T is the absolute temperature, k is Boltzman constant. I is the diode current, v is
the voltage across the diode. Equation–- may be rewrite as a series using Taylor
expansion, in order to analyze the rectifing process.
I = Is (αv +
(αv)2 (αv)3
(αv)n
+
+ ....
2!
3!
n!
for small signal operation (αv < 1) only the the first two term are significant,
so the diode is said to be operating in the square law region. Mathematically it can be
Power Sensing Method
15
Current
80µΑ
60µΑ
40µΑ
20µΑ
Voltage(v)
-0.06
-0.04
-0.02
0
Power(dBm)
0.02
-21
0.04
-15
0.06
-11.5
Figure 7 Small signal I-V characteristic of diode detector
Current(A)
0.2
0.15
0.1
0.05
Voltage(v)
0
70µ v
Power(dBm) -70
0.05
0.1
0.15
0.2
-13
3
4.8
6
0.25
7
0.3
8
Figure 8 Largel signal I-V characteristic of diode detector
prooved that the approximation of square law region is valid between the noise level
to about 20mv (-20dbm). In that region the output I (and output v on resistor), is
proportional to RF input voltage squared. When αv ∼ 1, (or between -20 dBm to 0
dBm ) the other term of equation-6.4 become significant, the diode response no longer
in law region, but according to quasi law region. above that range (0 to 20 dBm )
the diode moves into linear region, inthat region the output voltage is proportional
to input voltage.
For a typical diode, the square law region , exist from the noise level about
0.1nw (-70dBm) to 10µw (-20 dBm). the quasi square law region ranges from 10 µw
to 1 mw, and linear region extend from 1 mw to 100 mw.
Diode technology provides some 8000 times (40 dB.) more-efficient RF-toDC conversion compared to the thermocouple previously discussed. Diode sensor
technology excels in sensitivity, although thermocouple sensors maintain their one
16
Introduction
Pinc
Pref
Load
Figure 9 Measuring power using directional coupler
primary advantage as pure square-law detectors for the range -30 to +20 dBm. At
the detecting level of 0.1 nw (-70dBm) the diode detector output is about 50 nv, such
a very low signal requires special care to prevent mixing signal with noise. Today
broadband detectors span frequencies from 100 kHz to 50 GHz.
1.10.3 Directional Power Sensor
Directional sensors are connected between source and load, to measure the incident
and reflected power. They are constructed with a dual directional coupler, with
capability to separate between forward and reflected wave. The coupled signal are
measured by separate RF to DC converters (Schottky diode) for the incident and
for the reflected power. Fig.-12 shows a typical block diagram of directional power
sensors.
Some sensors can measure the peak power, the output signal of the sensors
being boosted and applied to a peak hold circuit before it is transferred to the power
meter. The directional coupler determines the main features of a directional power
sensor, such as measurement accuracy, matching, frequency and power range. Due to
rather small dimensions, line couplers with short secondary line directional couplers
with lumped components or similar designs are suitable for use with directional power
meters. For the frequency range up to 100 MHz, the lumped coupler mostly used.
Due to the directional coupler, directional power sensors are always somewhat more
narrowband than the terminating power sensors, covering a bandwidth between one
octave and little more than two decades. The rated power ranges from a few W to
some kW . It can relatively easily be influenced by the coupling ratio, with hardly
any change to the power absorbed by the directional sensor. Reflection coefficient
and insertion loss of the directional coupler are usually negligible. This holds true at
least for the lower band limit, where there is only a loose coupling between main line
and secondary line.
Chapter 2
EXPERIMENT PROCEDURE
2.1
Required Equipment
1. Oscilloscope HP − 54603B.
2. Signal Generator (SG)HP − 8647A.
3. Two Arbitrary Waveform Generators (AW G)HP − 33120A.
4. Power Meter HP-E4418B.
5. Power Sensor- HP-E4412A.
6. Double Balanced Mixer Mini-Circuit ZAD − 6.
6. Diode Detector Herotek DZM124NB..
7. Directional Coupler Waveline 9008-20.
8. Termination-50Ω .
2.2
Turning On the Power Meter
The following steps show you how to turn on the power meter and verify that it is
operating correctly.
1. Connect the power cord and turn on the power meter.
The front panel display and the green power LED light up when the power
meter is switched on. The power meter performs it’s power on self test.
2. Set the display contrast if required.
The display contrast is adjusted by pressing ↑ ª and ↓ ª . If these softkeys
are not displayed press Prev repeatedly until they appear.
3. Connect a power sensor.
Connect one end of the sensor cable to the power meter’s channel input and
the other end to the power sensor.
2.3
Front Panel Tour
Refer to Fig.-1
1. Preset -This hardkey allows you to preset the power meter if you are currently working in local mode (that is, front panel operation).
2. NH -This hardkey allows you to select the upper or lower measurement window on the power meter’s display. The window which is selected is highlighted by a
18
Experiment Procedure
12
11 10
9
POWER REF
1
-10 dBm
2
3
4
5
6
7
8
Figure 1 Front panel of power meter
shadowed box.
¤↔ ¤
-This hardkey allows you to choose either a one or a two window
¤
display.
3. ∅ | -This hardkey switches the power meter between on and standby.
When the power meter is switched to standby (that is, when this hardkey has not
been selected but the line power is connected to the instrument) the red LED is lit.
When the power meter is switched on the green LED is lit.
4. The System
hardkey allows access to softkey menus which affect the general
Input
power meter system setup, (for example the HP-IB address) and also to softkey menus
which effect the setup of the channel inputs.
Save
-This hardkey is the only one that is completely dedicated to the
5. Re
call
control of the power meter as a system.
Re f
dBm/w - These hardkeys allow access to same menus
6. Measure
Setup
Of f set
which affect the setup of the measurement windows.
requency
7. FCal
, Zero
- These hardkeys allow access to softkey menus which affect
F ac
Cal
the measurement channel.
8. Channel Input- The HP E4418B has one sensor input.
9. POWER REF Output- The power reference output is a 50Ω type N connector. The output signal sinewave of 1 mW at 50 MHz is used for calibrating the
sensor and meter combination.
10. ⇑ ⇓ ⇐= =⇒ -Arrow hardkeys allow you to move the position of the
cursor, use select fields for editing, and edit alphanumeric characters.
11. More -Menu related hardkeys this hardkey allows you to move through all
pages of a menu. The bottom right of the power meter display indicates the number
of pages in the menu. For example, if ”1 of 2” is displayed, pressing More moves
you to ”2 of 2”. Pressing More again moves you back to ”1 of 2”.
Prev This hardkey allows you to move back one level in the softkey menu.
Power Meter Operation
19
-10 dBm
POWER
REF
Figure 2 Zeroing and Calibrating Power Meter
Repeatedly pressing Prev accesses a menu which allows you to increase and decrease
the display contrast.
12. Softkeys- These four keys are used to make a selection from the menus.
2.4
Power Meter Operation
2.4.1 Zeroing the Power Meter
Zeroing adjusts the power meter for a zero power reading with no power applied to
the power sensor. During zeroing, which takes approximately 10 seconds, the wait
symbol is displayed. To zero the power meter:
Zeroing of the power meter is recommended:
* when a 5◦ C change in temperature occurs since the last calibration.
* when you change the power sensor.
* every 24 hours.
* prior to measuring low level signals. For example, 10 dB above the lowest
specified power for your power
1. Connect the power sensor to the POWER REF output as indicated in
Fig-2.
, Zero . During zeroing the wait symbol is displayed.
1. Press Zero
cal
2.4.2 Calibrating the Power Meter
Calibration sets the gain of the power meter using a 50 MHz 1 mW calibrator as a
traceable power reference. The power meter’s POWER REF output is used as the
signal source for calibration. An essential part of calibrating is setting the correct
reference calibration factor for the power sensor you are using. The HP E-4412A
power sensors set the reference calibration factor automatically. During calibration
the wait symbol is displayed. The power meter identify that an HP E-series power
sensor is connected and will not allow you to select certain softkeys. The text on
these softkeys appears grayed out.
Note
During calibration the power meter automatically switches the power reference
calibrator on (if it is not already on), then after calibration it switches it to the state
it was in prior to the calibration.
1. Verify that the system is connected as indicated In Fig.-2
20
Experiment Procedure
15.000,000 MHz
R
HP-33120A
15.000,000 MHz
I
Oscilloscope 54600A
L
Figure 3 Average power of sinusoidal signa
2. Press
Zero
Cal
3. Press: cal to calibrate the power meter. During calibration the wait symbol
is displayed. (The power meter automatically turns on the POWER REF output.)
2.5
Average Power
In this part of the experiment, we use two sinusoidal waveforms to represent the
voltage and the current respectively. The Double Balanced Mixer used as a multiplier
with losses, which multiply the voltage and the current respectively. The oscilloscope
used as the display of the power meter.
1. Refer to appendix-1, connect the system according to appendix, and set
the phase between the two generators to zero degree.
2. Connect the System according to Fig.- 3.
3. Adjust the T &M equipment as follows:
LO − AW G- Frequency 1 kHz amplitude 100 mv.
RF − AW G- Frequency 1 kHz amplitude 100 mv.
4. Measure the two signals according to table-1, and save the data on magnetic
media.
Frequency Vp−p Vave
power
.
Voltage
Table-1
Why is Vave of the voltage signal significantly smaller than the Vave of the
power signal?
5. Set the phase between the two generators to +90◦ ,describe what happens
to the power signal, and what is the meaning of these changes?
6. Set the phase between the two generators to -90◦ describe what happens
to the power signal generators to -90◦ what is the difference +90◦ and -90◦ ? Set the
phase between the two generators to +90◦ ,-90◦ , and save the data on magnetic media
Power of a Modulated Sinusoidal Signal
21
15.000,000 MHz
R
HP-33120A
15.000,000 MHz
I
Oscilloscope 54600A
L
Figure 4 Power of AM modulated signal
for each phase difference.
2.6
Power of a Modulated Sinusoidal Signal
In this part of the experiment, we multiply two identical AM signal sources, in order
to simulate three types of power (average power, peak power, peak envelope peak)
used in measuring modulated sinusoidal signals .
1. Connect the System according to Fig. -4.
2. Set the frequency of the two AWG’s to 20 kHz,and set the phase to 0◦
between them.
3. Adjust the T &M equipment as follow:
LO−AW G- Frequency 20 kHz amplitude 400 mv , AM modulation, modulated
frequency 1 kHz, AM depth 70%.
RF − AW G- Frequency 20 kHz amplitude 100 mv , AM modulation, modulated frequency 1 kHz, AM depth 70%.
4. Adjust the oscilloscope in order to get a stable signal like Fig-3 (theory
chapter), and save the data on magnetic media.
2.7
Pulse Power
In this part of the experiment, we measure the major parameter of a pulse, generated
by a square wave signal with offset and duty cycle.
1. Connect the System according to Fig.-5 .
2.Adjust the AWG to: Square wave , Frequency 1 MHz , amplitude 100 mv
,offset 50 mv,duty cycle 20%.
3. Using the oscilloscope feature measure
a. Zero to peak power, (without the over and under shoot of the pulse),
b. Pulse width,
c. Pulse Repetition Interval (PRI).
d. Average power.
22
Experiment Procedure
Oscilloscope 54600A
15.000,000 MHz
HP-33120A
Figure 5 Power of pulse signal
Digital multimeter
515.000,00
MHz
10.000,00 V
DC
Diode
Detector
HP-34401A
Signal generator HP-8647A
Figure 6 Measuring power using diode detector
e. Pulse Repetition Frequency (PRF).
f. Duty cycle of the pulse
save the Pulse on magnetic media.
2.8
Diode Detector
In the first part of the experiment you will sketch the characteristic curve voltage
as a function of input power. In the second part you will measure the power of an
’unknown’ source .
1. Connect the diode detector to the signal generator as indicated in Fig.-6.
2. Set the signal generator to 500 MHz, amplitude according to table-2, measure the output voltage and fill in the table.
Final Report
23
P(dBm) Diode Voltage P(dBm) Diode Voltage
-50
-15
-45
-10
-40
-7
-35
-5
-30
0
-25
3
-20
5
-17
10
Table-2
2.9
Final Report
1. Using the data of average and instantaneous power , draw three graphs of average
power for 0◦ ,90◦ ,-90◦ , ( answer the relevant questions in this pharagraph).
2. Using the data of Power of a Modulated Sinusoidal Signal draw a graph
like figure-3(theory part), but based on measured data.
a. Using Matlab or other software, draw a graph of 20 kHz AM- signal,
modulated by 1 kHz, AM depth of 70%. (See instantaneous power Fig.-3 theory
part).
b. A graph of calculated average power (Pave ).
c. A graph of calculated envelope power Pe(t) (based on average of every
cycle of instantaneous power).
d. Find the PEP from the above calculation.
3. Referring to your data of pulse measurement , draw a graph of
a. Pulse power
b. Average power of the pulse(calculated).
From the data find peak power, PRF, duty cycle of the pulse.
4. Use the data of table-2, draw a graph of the diode (Vin (calculated) as a
function of output voltage). Using regression function (with statistical software or
worksheet ) find the best equation of the curve. According to the graphs find the
range where the output voltage of the diode is approximately proportional to the
input power, and the range that the output voltage is proportional to input voltage.
2.10
Appendix-1
2.10.1 To phase lock two function generator.
1. Connect rear- panel Ref Out 10MHz output terminal of the master Arbitrary
Waveform Generator HP-33120A to Ref in on the rear panel of the slave HP-33120A
as indicated in Fig-9.
2. Connect the two AWG’s to the oscilloscope as shown in figure-9
3. Set the oscilloscope to XY function, in order to measure phase difference.
24
Experiment Procedure
Ref Out Ext Ref in
Ref Out Ext Ref in
Rear panel connection.
15.000,000 MHz
Oscilloscope 54600A
Oscilloscope
display
HP-33120A
15.000,000 MHz
Figure 7 Setting zero phase using Lissajous method
4. Turn on the menu of the AWG by pressing shift Menu On/Off the display
then looks like A: MOD MENU .
5. Move across to G: PHASE MENU by pressing the < button.
6. Move down one level to the ADJUST command, by pressing ∨, the display
looks like 1: ADJUST
5. Press ∨ one level and set the phase offset, Change the phase continuously
between the two AWG’s until you get straight line, incline at 45◦ to the X axis (zero
phase). you see then a display like ∧120.000DEG .
6. Turn off the menu by pressing ENTER .You have then exited the menu.
2.10.2 Setting a zero phase reference at the end of the cable.
1. Turn on the menu by pressing shift Menu On/Off the display looks like A: MOD MENU
.
2. Move across to the PHASE MENU choice on this level, by pressing <, the
display looks like G: PHASE MENU
3. Move down one level and then across to the SET ZERO by pressing ∨ and
> bottoms, the display show the message 2: SET ZERO .
4. Move down a level to set the zero phase reference, by pressing ∨ the
displayed message indicates PHASE = 0 .
5. Press Enter , save the phase reference and turn off the menu.
Important
Appendix-1
25
1. At this point, the function generator HP-33120A is phase locked to another
HP-33120A or external clock signal with the specified phase relationship. The two
signals remain locked unless you change the output frequency.