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 71.1 Prelab Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.2 Background Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.3 dB and dBm Terminology . . . . . . . . . . . . . . . . . . . . . . . . 71.4 Fundamentals of RF Power Measurement . . . . . . . . . . . . . . . . 81.5 Microwave Power Meter -HP-E4418 . . . . . . . . . . . . . . . . . . . 9

1.5.1 Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . 91.6 Types of Power Measurements . . . . . . . . . . . . . . . . . . . . . . 101.7 Average and Instantenous Power . . . . . . . . . . . . . . . . . . . . 101.8 Power of Modulated Sinusoidal Signal . . . . . . . . . . . . . . . . . . 111.9 Pulse Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.10 Power Sensing Method . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.10.1 Thermocouple as a sensor of Power meter. . . . . . . . . . . . 131.10.2 Diode as a Sensor of Power Meter . . . . . . . . . . . . . . . . 141.10.3 Directional Power Sensor . . . . . . . . . . . . . . . . . . . . . 16

2 Experiment Procedure 172.1 Required Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.2 Turning On the Power Meter . . . . . . . . . . . . . . . . . . . . . . 172.3 Front Panel Tour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.4 Power Meter Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.4.1 Zeroing the Power Meter . . . . . . . . . . . . . . . . . . . . . 192.4.2 Calibrating the Power Meter . . . . . . . . . . . . . . . . . . . 19

2.5 Average Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.6 Power of a Modulated Sinusoidal Signal . . . . . . . . . . . . . . . . 212.7 Pulse Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.8 Diode Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222.9 Final Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.10 Appendix-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.10.1 To phase lock two function generator. . . . . . . . . . . . . . . 232.10.2 Setting a zero phase reference at the end of the cable. . . . . . 24

4 CONTENTS

Part I

Experiment-4 Power Meter andPower Measurement

5

Chapter 1

INTRODUCTION

1.1 Prelab Exercise

1. Define average power, Instantaneous power, PEP, thermocouple principle, squarelaw region of diode.

2. Describe how you intend to measure incident and reflected power usingdirectional coupler.

1.2 Background Theory

At low frequencies, the strength of the signal is calculated by measuring the voltage orcurrent. Voltage and current are related by Ohm’s law (current= voltage÷impedance),and power defined as the product of voltage and current. At microwave frequenciesthe equivalents to voltage is electric field, and magnetic field to current. It is not aneasy task to measure accurately magnetic and electric fields. Power is the quantitythat is measured and the magnetic and electric fields are derived from the measuredpower. Power is the amplitude of the electromagnetic wave, and is measured in unitsof watts, which related to mechanics units as watt (W ) = 1 joule/sec. At microwavefrequencies, the reference level of power is not 1 W , but 1 mW . The reason is thata milliwatts of power is enough to operate microwave devices and components, andeven wireless products. Techniques for power measurements depend on frequency.Below 100kHz, voltage and current are practically measured. At frequencies of tenshundreds of MHz, power measurement is more accurate then the power calculated bymeasuring voltage and current. Above 1GHz, power measurement is dominant andcurrent 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 forhigh powers ( more than 1watt), and the zeroes for low powers make the calculationcumbersome. For convenience and the cases we perform relative power measurement,for example, to compare the output power coming out of amplifier, relative to thatgoing into it. the dB system of units is used and expressed as :

8 Introduction

P [dB] = 10 log10(P

Pref) (1.1)

The dB number system can also be used to express absolute value of microwavepower as dBm and defined as:

P [dBm] = 10 log10(P

1mW) (1.2)

Watts dBm designation1,000,000 90 1 megawatt1,000 50 1 kilowatt1 30 1 watt0.001 0 1 milliwatt0.000,001 -30 1 microwatt0.000,000,001 -60 1 nanowatt0.000,000,000,001 -90 1 picowatt0.000,000,000,000,001 -120 1 femtowattTable-1 Prefix used to specify microwave power

1.4 Fundamentals of RF Power Measurement

The measurement of power in RF and microwave applications has the same signif-icance as voltage measurements in electrical engineering. Power meters are usedfor a wide variety of measurement tasks. In comparison with spectrum or networkanalyzers, they are relatively cheap and unsophisticated instruments.

The development of carrier-based telecommunications at the beginning of thiscentury derived a parallel development in the field of power measurements. The ma-jority of methods were based on converting electrical energy into heat(Thermistorand thermocouple devices). For a long time, this was the only way of making ac-curate measurements at practically any frequency. In the meantime, direct voltageand current measurements can be made up into the GHz range assuming matchedsystem without having to convert electrical energy into heat. Nevertheless, the in-tensity of RF and microwave signals is still given in terms of power. Apart from thehigh accuracy of thermal power meters, there are other important reasons for usingpower. Any signal transmission by waves, for example sound propagation, involvesthe transfer of energy. Only the rate of energy flow, power, is an absolute measure ofwave intensity. In the RF and microwave ranges, the wave properties of the electro-magnetic field play an important role because the dimensions of the lines used are ofthe same order of magnitude as the wavelength used. This fact has to be taken intoaccount when the quantity to be measured . Voltage and current are less appropri-ate because they depend on the physical characteristics of the transmission medium(dimensions, dielectric constant, permeability) and field strength. Consider, for ex-ample, two matched coaxial cables with characteristic impedance of 50Ω and 75Ω.

Microwave Power Meter -HP-E4418 9

MatchingNetwork

RFInput

TemperatureSensor

BPFSignal

cocditioning

MicroProcessor

Chopperdriver

ADC

DisplayBusCalibrator

Diode Sensor Power Meter

EEPROM

DSP

Figure 1 Block diagram of Power Meter with Diode Sensor

For the same transmitted power, the voltage and current for the two impedance differby a factor of 1.22. here are further reasons for selecting power as the quantity to bemeasured. 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 advancedto the point where dramatically-improved performance and capabilities are availablefor diode power sensing and metering power sensors are now capable of measuringover a wide dynamic - 70 to +20 dBm, range of 90 dB . This permits the new sensorsto be used for CW applications which previously required two sensors.

The new HP ECP-E18A power sensor features a frequency range 10 MHz to18 GHz. A simplified block-diagram of the sensor is shown in Figure-1 . The frontend construction is combines the matching input pad ( low value Attenuator), diodes,FET choppers, integrated RF filter capacitors, a driving pre-amplifier. All of thosecomponents operate at such low levels that it was necessary to integrate them intoa single thermal space on a surface-mount-technology PC board. To achieve theexpanded dynamic range of 90-dB, the sensor/meter architecture depends on a datacompensation algorithm, which is calibrated and stored in an individual EEPROM ineach sensor. The data algorithm stores information of three parameters, input powerlevel versus frequency versus temperature for the range 10 MHz to 18 and - 70 to +20dBm and 0 to 55 C. At the time of sensor power-up, the power meter interrogates theattached sensor, using an industry-standard serial bus format, and in turn, receivesthe upload of sensor calibration data. An internal temperature sensor supplies thediode’s temperature data for the temperature-compensation algorithm in the powermeter. The new sensor store cal-factor tables for two different input power levels to

10 Introduction

PowerVoltageCurrent

Ampl

itude

t

Average Power

Amplitude of sinusoidal power (solid line), voltage (dashed line), current (dash-dotted line), and average power (dotted line) as function of time. θ is the phasedifference between current and voltage.

θ

Figure 2 Average and Instantenous power

improve accuracy of the correction routines. Figure -1 shows a simplified schematicof the HP EPM-4418A meter. The pre-amplified sensor output signal receives someearly amplification, followed by some signal conditioning and filtering. The signal isthen applied to a dual ADC. A serial output from the ADC takes the sampled signalsto the digital signal processor, which is controlled by the main microprocessor. Adifferential drive signal, synchronized to the ADC sampling clock, is output to thesensor for its chopping function.The ADC provides a 20-bit data stream to the digitalsignal processor, which is under control of the main microprocessor. Even the syn-chronous detection is performed by the ADC and DSP rather than use of a traditionalsynchronous 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 peakenvelope power. The first is suitable for energy transfer considerations, the secondtype deals with square shape power pulses as function of time, and the last with amore complicated shapes of power as function of time. The pulse power measurementgives 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 ofsingle power measurements is performed, such that the needed details of the poweras 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 ofcurrent 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 currenti(t) = Im cos(wt+ θi)

Then the power will be

p(t) = v(t)i(t) = Vm cos(wt+ θv)Im cos(wt+ θi)

by using the trigonometric identity cos θ1 cos θ2 = 12[cos(θ1 − θ2) + cos(θ1 + θ2)]

we get

p(t) =VmIm2

cos(θv − θi) +VmIm2

cos(2wt+ θv + θi)

by using the trigonometric identity cos(θ1 + θ2) = cos θ1 cos θ2 − sin θ1 sin θ2we get

p(t) =VmIm2

cos(θv − θi) + (1.3)

+VmIm2

cos(θv + θi) cos 2wt− VmIm2

sin(θv + θi) sin 2wt

the following points can be made concerning equation-6.3 and Fig.-21. The average value of the power (or the DC component) is given by VmIm

2cos(θv−

θi) and has maximum when the phase difference between current and voltage equalzero.

2. The frequency of the instantenous power is twice the frequency of voltageor current.

3. If the phase difference between voltage and current is +π/2, the circuitis purely inductive and the average power will be zero ,power will oscillate betweensource and inductor.

4. If the phase difference between voltage and current is -π/2, the circuit ispurely cacitive and the average power will be zero ,power will oscillate between sourceand capacitor.

1.8 Power of Modulated Sinusoidal Signal

When modulated sinusoidal signals are applied, other definitions of power are moreappropriate to the system (Fig-3). The average of P over the modulation period iscalled the average power Pavg. This is what a thermal power meter would indicate.

The power averaged over one period of a carrier is referred to as the envelopepower Pe(t). It varies in time with the modulation frequency. The maximum envelopepower is referred to as the peak envelope power or PEP . PEP is an importantparameter for specifying transmitters. PEP and the envelope power can only bemeasured with peak or envelope power meters, which use fast diode sensors.

12 Introduction

AM voltage signal

Average PowerEnvelope Power

Instantaneous Power

PEP

t

t

p

V

0

0

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 consideredto be the time between the 50 percent rise-time and fall time amplitude points ( seeFig-4). Pulse power is defined by

P =1

τ

τZ0

v(t)i(t)dt

By definition, pulse power is averages out any aberrations in the pulse envelope suchas overshoot or undershoot ringing.

The definition of pulse power has been extended since the early days of mi-crowave to be:

Pp =Pavg

Duty Cycle

where duty cycle is the pulse width times the repetition frequency. This extendeddefinition, allows calculation of pulse power from an average power measurement andthe 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 anaverage power sensor. One reason is that the instrumentation is less expensive, andin a technical sense, the averaging technique integrates all the pulse imperfectionsinto 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 anaverage power sensor.

Power Sensing Method 13

pulse width τPRI=1/PRF

Average Power

Pulse topamplitude

PRI

Time

Pow

er τDuty cycle=PRF.

Figure 4 Common Pulse Parameters

* Thermocouple* Diode

* Directional-Coupler

Sensing elements

powerMeter

RFinput

Substituted DCor AC Signal

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 signalthat 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, anddirectional 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 volt-age due to temperature differences between a hot and a cold junction. If the twometals are put together in a closed circuit, current will flow due to the difference inthe voltages. If the loop remains closed, current will flow as long as the two junc-tions remain at different temperatures. In a thermocouple, the loop is broken anda sensitive DC voltmeter is inserted to measure the net thermoelectric voltage (seeFig-6). The measuring voltage can be related to a temperature change due to RFpower incident upon the thermocouple element.

14 Introduction

metal-1

metal-2

Hot-junctionVdc Cold junction

Figure 6 Thermocouple principle

Since the voltage produced in a thermocouple is very low, it is possible toconnect several junction in series in order to yield larger thermoelectric voltage. Thetwo main reasons for wide using thermocouple technology are: Thermocouple ex-hibit wider dynamic range than thermistor technology, and they feature an inherentsquare-law detection characteristic proportional to DC . Since thermocouples, likethermistors with a self-balancing bridge, always respond to the true power of a sig-nal, 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 lowermeasurement 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 measure-ments at microwave frequencies. Diodes convert high frequency energy to DC byusing rectification properties, inherent to their non-linear current-voltage (i-v) char-acteristics. The advantage of the diode is that they can be used for measurement ofextremely low powers. Refer to Fig-8 and Fig.-9 You can see that their square-lawregion begin from -70 to -30 dBm.

Mathematically, a detection diode obeys the diode detection

I = Is(eqvkt − 1) = Is(e

αv − 1) (1.4)

α =q

kt

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 isthe voltage across the diode. Equation–- may be rewrite as a series using Taylorexpansion, in order to analyze the rectifing process.

I = Is(αv +(αv)2

2!+(αv)3

3!+ ....

(αv)n

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

-0.06 -0.04 -0.02 0 0.02 0.04 0.06

80µΑ

60µΑ

40µΑ

20µΑ

Voltage(v)

Cur

rent

Power(dBm) -21 -15 -11.5

Figure 7 Small signal I-V characteristic of diode detector

0

0.05

0.1

0.15

0.2

0.05 0.1 0.15 0.2 0.25 0.3Voltage(v)

Cur

rent

(A)

Power(dBm)

70µv

-70 -13 3 4.8 6 7 8

Figure 8 Largel signal I-V characteristic of diode detector

prooved that the approximation of square law region is valid between the noise levelto about 20mv (-20dbm). In that region the output I (and output v on resistor), isproportional to RF input voltage squared. When αv ∼ 1, (or between -20 dBm to 0dBm ) the other term of equation-6.4 become significant, the diode response no longerin 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 proportionalto input voltage.

For a typical diode, the square law region , exist from the noise level about0.1nw (-70dBm) to 10µw (-20 dBm). the quasi square law region ranges from 10 µwto 1 mw, and linear region extend from 1 mw to 100 mw.

Diode technology provides some 8000 times (40 dB.) more-efficient RF-to-DC conversion compared to the thermocouple previously discussed. Diode sensortechnology 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. Atthe detecting level of 0.1 nw (-70dBm) the diode detector output is about 50 nv, sucha very low signal requires special care to prevent mixing signal with noise. Todaybroadband 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 incidentand reflected power. They are constructed with a dual directional coupler, withcapability to separate between forward and reflected wave. The coupled signal aremeasured by separate RF to DC converters (Schottky diode) for the incident andfor the reflected power. Fig.-12 shows a typical block diagram of directional powersensors.

Some sensors can measure the peak power, the output signal of the sensorsbeing boosted and applied to a peak hold circuit before it is transferred to the powermeter. The directional coupler determines the main features of a directional powersensor, such as measurement accuracy, matching, frequency and power range. Due torather small dimensions, line couplers with short secondary line directional couplerswith lumped components or similar designs are suitable for use with directional powermeters. For the frequency range up to 100 MHz, the lumped coupler mostly used.Due to the directional coupler, directional power sensors are always somewhat morenarrowband than the terminating power sensors, covering a bandwidth between oneoctave and little more than two decades. The rated power ranges from a few W tosome kW . It can relatively easily be influenced by the coupling ratio, with hardlyany change to the power absorbed by the directional sensor. Reflection coefficientand insertion loss of the directional coupler are usually negligible. This holds true atleast for the lower band limit, where there is only a loose coupling between main lineand 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 (AWG)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 isoperating 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.-11. Preset -This hardkey allows you to preset the power meter if you are cur-

rently working in local mode (that is, front panel operation).2. NH -This hardkey allows you to select the upper or lower measurement win-

dow on the power meter’s display. The window which is selected is highlighted by a

18 Experiment Procedure

POWER REF

-10 dBm1

3

2

4 5 6 7 8

9101112

Figure 1 Front panel of power meter

shadowed box.¤↔ ¤

¤ -This hardkey allows you to choose either a one or a two windowdisplay.

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 notbeen 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 SystemInput

hardkey allows access to softkey menus which affect the general

power meter system setup, (for example the HP-IB address) and also to softkey menuswhich effect the setup of the channel inputs.

5. SaveRe call -This hardkey is the only one that is completely dedicated to the

control of the power meter as a system.

6. MeasureSetup

Re fOffset

dBm/w - These hardkeys allow access to same menus

which affect the setup of the measurement windows.

7. FrequencyCal Fac

, ZeroCal

- These hardkeys allow access to softkey menus which affectthe 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 con-

nector. The output signal sinewave of 1 mW at 50 MHz is used for calibrating thesensor and meter combination.

10. ⇑ ⇓ ⇐= =⇒ -Arrow hardkeys allow you to move the position of thecursor, use select fields for editing, and edit alphanumeric characters.

11. More -Menu related hardkeys this hardkey allows you to move through allpages of a menu. The bottom right of the power meter display indicates the numberof pages in the menu. For example, if ”1 of 2” is displayed, pressing More movesyou 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

POWERREF

-10 dBm

Figure 2 Zeroing and Calibrating Power Meter

Repeatedly pressing Prev accesses a menu which allows you to increase and decreasethe 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 tothe power sensor. During zeroing, which takes approximately 10 seconds, the waitsymbol is displayed. To zero the power meter:

Zeroing of the power meter is recommended:* when a 5C 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 power1. Connect the power sensor to the POWER REF output as indicated in

Fig-2.1. Press Zero

cal, Zero . During zeroing the wait symbol is displayed.

2.4.2 Calibrating the Power Meter

Calibration sets the gain of the power meter using a 50 MHz 1 mW calibrator as atraceable power reference. The power meter’s POWER REF output is used as thesignal source for calibration. An essential part of calibrating is setting the correctreference calibration factor for the power sensor you are using. The HP E-4412Apower sensors set the reference calibration factor automatically. During calibrationthe wait symbol is displayed. The power meter identify that an HP E-series powersensor is connected and will not allow you to select certain softkeys. The text onthese softkeys appears grayed out.

NoteDuring 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 stateit 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

HP-33120A

15.000,000 MHz

Oscilloscope 54600AR

L

I

Figure 3 Average power of sinusoidal signa

2. Press ZeroCal

3. Press: cal to calibrate the power meter. During calibration the wait symbolis 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 thevoltage and the current respectively. The Double Balanced Mixer used as a multiplierwith losses, which multiply the voltage and the current respectively. The oscilloscopeused as the display of the power meter.

1. Refer to appendix-1, connect the system according to appendix, and setthe 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 −AWG- Frequency 1 kHz amplitude 100 mv.RF −AWG- 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

powerVoltage

Table-1Why 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 thephase 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

HP-33120A

15.000,000 MHz

Oscilloscope 54600AR

L

I

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 orderto 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−AWG- Frequency 20 kHz amplitude 400 mv , AMmodulation, modulated

frequency 1 kHz, AM depth 70%.RF − AWG- Frequency 20 kHz amplitude 100 mv , AM modulation, modu-

lated 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, generatedby 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 measurea. 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

15.000,000 MHz

HP-33120A

Oscilloscope 54600A

Figure 5 Power of pulse signal

515.000,00MHz

Signal generator HP-8647A

DiodeDetector

10.000,00 VDC

HP-34401A

Digital multimeter

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 voltageas 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, mea-sure 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 averagepower for 0,90,-90, ( answer the relevant questions in this pharagraph).

2. Using the data of Power of a Modulated Sinusoidal Signal draw a graphlike 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 theorypart).

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 ofa. Pulse powerb. 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 orworksheet ) find the best equation of the curve. According to the graphs find therange where the output voltage of the diode is approximately proportional to theinput 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 ArbitraryWaveform Generator HP-33120A to Ref in on the rear panel of the slave HP-33120Aas indicated in Fig-9.

2. Connect the two AWG’s to the oscilloscope as shown in figure-93. Set the oscilloscope to XY function, in order to measure phase difference.

24 Experiment Procedure

15.000,000 MHz

HP-33120A

15.000,000 MHz

Oscilloscope 54600AOscilloscope

display

Ref Out Ext Ref in Ref Out Ext Ref in

Rear panel connection.

Figure 7 Setting zero phase using Lissajous method

4. Turn on the menu of the AWG by pressing shift Menu On/Off the displaythen 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: ADJUST5. 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 (zerophase). 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 <, thedisplay 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 ∨ thedisplayed 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 anotherHP-33120A or external clock signal with the specified phase relationship. The twosignals remain locked unless you change the output frequency.