RF Training Module PDF

8/8/2019 RF Training Module PDF

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Honeywell Technology Solutions Inc.

Goddard Corporate Park

Lanham, Maryland 20706-2291

RF Training Module(Test & Integration Department Presentation Package)

Original

February 2009


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What is RF?

Basic Definition

Basic RF Terminology

RF Bands

Basic RF systems from Spacecraft to Ground Segment

Transponders

Transceivers Antennas

Transmission Lines

Transmitters/Exciters

Amplifiers

Receivers

Description of Basic RF test equipment Signal Generator

Spectrum Analyzer

Power meter

Counter

Basic RF equations

Space and Cable loss

Link Calculations

Noise Figure

Useful WEB Sites and References

Lab Demonstration

RF TRAINING MODULE OUTLINE

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RF (Radio frequency) is a frequency or rate of oscillation within the range of about 3 Hzto 300 GHz.

Since most of this range is beyond the vibration rate that most mechanical systems canrespond to, RF usually refers to oscillations in electrical circuits or electromagneticradiation.

Electrical currents that oscillate at RF have special properties not shared by direct currentsignals.

One such property is the ease with which it can ionize air to create a conductive paththrough air.

Another special property is an electromagnetic force that drives the RF current to thesurface of conductors, known as the skin effect which is useful when designing RFcircuits.

Another property is the ability to appear to flow through paths that contain insulatingmaterial, like the dielectric insulator of a capacitor.

The degree of effect of these properties depends on the frequency of the signals.

Basic Definition

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Hertz (Hz)

A term representing cycles/second (cps).

The unit of measure is named after Heinrich Hertz, German physicist.

For example, 1 Hz means that an event repeats once per second, 2 Hz is twice persecond, and so on.

Frequency

The number of occurrences of a repeating event per unit time.

For example:

The frequency of the standard pitch A above middle C on a piano is usuallydefined as 440 Hz, (440 cps).

In North America the frequency of the alternating current (AC) is 60 Hz.

Visible light from deep red to violet has frequencies of 430 to 750 THz

(Terahertz).

RF Terminology

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Wavelength ()

The wavelength is related to the frequency by the formula: wavelength = wave speed/ frequency.

For example: = c/f, where c is the speed of light (in meters/sec) and f is

frequency (Hz).

Higher frequencies have shorter wavelengths.

Lower frequencies have longer wavelengths.

Frequency Multipliers

Hz (Hertz) Cycles/Second 1 Hz

kHz (kilohertz) One Thousand Hertz 1,000 Hz

MHz (megahertz) One Million Hertz 1,000,000 Hz

GHz (gigahertz) One Billion Hertz 1,000,000,000 Hz

THz (terahertz) One Trillion Hertz 1,000,000,000,000 Hz

RF Terminology

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Decibel (dB)

A logarithmic unit of measurement that expresses the magnitude of a physicalquantity (usually power or intensity) relative to a specified or implied reference level.

This reference levelis represented by a suffix.

For example: "dBm" indicates the reference quantity is one milliwatt (onethousandth of a watt) and dBW indicates the reference quantity is one Watt.

Since it expresses a ratio of two quantities with the same unit, it is dimensionless.

It has a number of advantages, such as the ability to represent very large or smallnumbers.

For example: LOG10(1,000,000) = 6; LOG10(0.000001) = -6

It has the ability to carry out multiplication of ratios by simple addition and subtraction.

For example: Doubling output power is 3 dB while a quadrupling is 6 dB.Therefore, if the antenna gain is doubled (3 dB) and the transmitter power isquadrupled (6 dB), the overall improvement is 3 + 6 = 9 dB.

Insertion Loss (I.L.)

The transmission loss from input to output, measured in dB.

RF Terminology

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VSWR (Voltage Standing Wave Ratio)

SWR is simply the ratio of the resistance of the termination and the characteristicimpedance of the line.

For example:A 75 ohm load will give an SWR of 1.5 when used to terminate a 50 ohmcable since 75/50 = 1.5.

Return Loss (R.L.)

The ratio of the power reflected back from the line to the power transmitted into theline.

Reflective Loss

The transmission loss due to the reflection of power at a discontinuity (mismatch).

For example: Applying a signal from a 50 ohm source into a 90 ohm receptor is animpedance mismatch.

Watt

It measures the rate of energy conversion.

Using the units of ampere and volt, work (energy) is done at a rate of one watt whenone ampere flows through a potential difference of one volt.

For Example: 1 watt = 1A x 1V; 120VAC applied to a 100W bulb draws 0.833 A

RF Terminology

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Bandwidth

In terms of RF, Bandwidth is the difference between the upper and lower cutoff

frequencies.

Can refer to a filter, a communication channel, an antenna or a signal spectrum, andis typically measured in hertz.

RF Terminology

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A graph of a bandpass filter's gain

magnitude, illustrating the concept of -3

dB (or half-power) bandwidth.


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Microwave data links, radio astronomy, remote

sensing, advanced weapons systems, advanced

security scanning

1 to 10 mm30 to 300 GHzEHFExtremely High

Frequency

Wireless networks, satellite links, microwave links,

satellite TV, door openers

1 to 10 cm3 to 30 GHzSHFSuper High Frequency

Broadcast television, mobile telephones, cordlesstelephones, wireless networking, remote keyless

entry for cars, microwave ovens, GPR

10 to 100 cm300 to 3000 MHzUHFUltra High Frequency

FM Broadcasting, broadcast television, aviation,

GPR

1 to 10 m30 to 300 MHzVHFVery High Frequency

Shortwave, amateur radio, citizens band radio10 to 100 m3 to 30 MHzHFHigh Frequency

Navigational Beacons, AM Broadcasting, maritime and

aviation communication

100 m to 1 km300 to 3000 KHzMFMedium Frequency

AM broadcasting, Navigational beacons, Low FER1 to 10 km30 to 300 KHzLFLow Frequency

directly audible when converted to sound (below ca. 18-

20 kHz; or ultrasound" 20-30+ kHz)

10 to 100 km3 to 30 KHzVLFVery Low Frequency

directly audible when converted to sound,

communication with mines

100 to 1000 km300 to 3000 HzULFUltra Low Frequency

directly audible when converted to sound, AC power

grids (50 hertz and 60 hertz)

1000 to 10000 km30 to 300 HzSLFSuper Low Frequency

directly audible when converted to sound,

communication with submarines

10,000 to 100,000 km3 to 30 HzELFExtremely Low

Frequency

APPLICATIONWAVELENGTHFREQUENCYSYMBOLNAME

RF Bands

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Military Radar Bands

UHF1 0.3 m300 1000 MHz

HF100 10 m3 30 MHz

VHF10 -1 m30 300 MHz

u mm300 3000 GHz

mm2.7 1.0 mm110 300 GHz

W4.0 2.7 mm75 110 GHz

V7.5 4.0 mm40 75 GHz

Ka11.1 7.5 mm27 40 GHz

K1.67 1.11 cm18 27 GHz

Ku2.5 1.67 cm12 18 GHz

X3.75 2.5 cm8 12 GHz

C7.5 3.75 cm4 8 GHz

S15 7.5 cm2 4 GHz

BANDWAVELENGTHFREQUENCY

RF Bands

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Basic RF Systems from Space to Ground Segment

+100Kz

Doppler

MOC

IP Cloud

GNCommand

System

Exciter

Ranging

Equipment

S-band TrackingData Processor GSFC FDFor

MOC

Tracking

Data

Acquisition Data IIRV

Recording/

Storage

Receivers

IP Cloud

Earth Horizon

Uplink

-100Kz

Doppler

2025-2120

MHz

PTP orFEP

Bit

Sync

2200-2300 MHz

Telemetry

Commands

& Ranging

** Not all stations have ranging

IP Encapsulated Data

MOC

PTP or

FEP

Downlink

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Basic RF Systems from Space to Ground Segment

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A transponder is the combination receiver/transmitter component of the communicationsubsystem that receives, processes, and transmits radio signals.

The term is a contraction of the words transmitter and responder.

Many spacecraft have multiple transponders for backup protection.

Transponders

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The transmitter and receiver are co-located in one unit and can be phase coherent withone another such that the transmit (downlink) carrier source is derived from and isphasecoherentwith the received (uplink) carrier from the ground station.

This coherency allows precise estimations of orbit and speed from measurements ofDoppler offset and rate of the downlink frequency at the ground station.

The XPNDR receives and detects digital command signals that control and configure thespacecraft.

The XPNDR transmits telemetered data from the spacecraft data subsystem which cancontain health status and science data.

The XPNDR demodulates the ranging signal contained in the uplink and re-modulates itonto the downlink.

Thus, by measuring the return propagation time, the distance between the groundstation and the satellite can be calculated.

Transponders

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Short for transmitter-receiver, a device that both transmits and receives analog or digital

signals.

In radio communications, a transceiver is a two-way radio that combines both a radio

transmitter and a receiver that exchanges information in half-duplex mode. The transmit frequency may be some ratio of the receive frequency but they are not

phase coherentwith one another.

Ranging and two way doppler cannot be performed when a spacecraft uses a

transceiver as its radio, but one way doppler can be performed.

Transceivers

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Antennas

Top Ten Antenna Questions

Frequency Range, Center Frequency, and Bandwidth

Minimum Gain (referenced dBd or dBi)

Maximum Allowable VSWR

Radiation Pattern: Omni or Directional

Polarization: Linear (Horizontal or Vertical); Elliptical (LHCP or RHCP)

Connector type (Male or Female)

Power Rating in Watts: Average and Peak

Maximum Physical Size

Where will the Antenna be mounted

Expected lifetime

Antennas

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Common Communication Antenna Types

TYPE Typical Gain (dBd)

Dipole 0

Omni 0

Gain Omni (Directional) 3 to 12

Mobile Whips -0.6 to 5.5

Corner Reflector 4 to 10

Log Periodic 3 to 8

Horn 5 to 12

Antennas

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Common Communication Antenna Types

TYPE Typical Gain (dBd)

Helix 5 to 15

Micro-Strip Patch 3 to 15

Yagi 3 to 20

Panel 5 to 20

Parabolic Dish 10 to 30

Antennas

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Gain Antenna performance is primarily established by its gain.

Gain must always be measured against a know reference.

Unfortunately, there are many "so-called" gain references.

Choosing the wrong reference could cost you up to 2.0 dB in performance.

Most commercial antenna suppliers specify gain in dBd (gain over a half-wavedipole).

The half-wave dipole has a very predictable radiation pattern similar to that of adonut.

Another reference, especially at microwave frequencies, is dBi.

This term refers to gain over an isotropic radiator, a theoretical antenna thatradiates equally well in all directions (such as the Sun).

If an antenna is specified in dBi gain, it will appear to have approximately 2.15 dB

higher gain than dBd. This may be a nifty way to impress the customer but it does not mean that you

get more gain if dBi is the reference.

Beware if the supplier only quotes antenna gain in just "dB". What is the reference?For instance, some mobile antennas are specified in dB gain over a quarter wavewhip which is about 0.6 dB less gain than a dipole.

Antennas

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VSWR (voltage-standing-wave-ratio) represents the degree with which an antenna is"matched" to the system impedance.

Most modern antennas, receivers and transmitters are designed for peakperformance when operating into a 50 Ohm transmission line.

If the VSWR is too high, the transmitter power may be reduced as well as thestrength of the received signal.

The typical commercial standard for maximum allowable VSWR across theentire bandwidth of a system is 1.5:1.

You should specify the maximum VSWR and the operating frequency bandwidth

when specifying your antenna. A VSWR of 2:1 or greater usually is considered unacceptable since it increases

losses in the transmission line.

Incidentally, decreasing the VSWR below 1.5:1 will often be expensive and will havelittle noticeable improvement.

Antennas

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Radiation Patterns

A graphical depiction of the relative field strength transmitted from or received by theantenna.

Antenna radiation patterns are taken at one frequency, one polarization, and one

plane cut.

plots in the plane of the axis is the azimuth or"E-plane"

plots in the plane perpendicular to the axis is the elevation or"H-plane

The patterns are usually presented in polar or rectilinear form with a dB strength

scale. Patterns are normalized to the maximum graph value, 0 dB, and a directivity is given

for the antenna.

This means that if the side lobe level from the radiation pattern were down -13dB, and the directivity of the antenna was 4 dB, then the sidelobe gain would be -9 dB.

Three types of plotting scales are in common usage; linear, linear logarithmic andmodified logarithmic.

Antennas

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Antennas

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Antennas

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Another popular antenna specification is the "front-to-back" (F/B) ratio.

It is defined as the difference in dB between the maximum gain or front of theantenna (usually 0 degrees) and a point exactly 180 degrees behind the front.

Another important antenna parameter is the side and rear lobe levels (if any).

In a well designed antenna they should typically be 10-15 dB below the main beam.

This parameter is often important but seldom seen on data sheets.

A good logarithmic plot will easily show such lobes and the direction where they aremaximum.

Antenna plots will assist in the proper aiming of the antenna for optimum performance onall the desired signals.

The narrower the beamwidth, the greater the difficulty in properly aiming the antenna.

Antennas

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Antenna Polarization

Most communications systems use either vertical, horizontal or circular polarization.

Knowing the difference between polarizations and how to maximize theirbenefit is very important to the antenna user.

A linearpolarized antenna radiates wholly in one plane containing the direction ofpropagation.

A circular polarized wave radiates energy in both the horizontal and vertical planesand all planes in between.

The difference, if any, between the maximum and the minimum peaks as theantenna is rotated through all angles, is called the axial ratio or ellipticity and isusually specified in decibels (dB).

If the axial ratio is near 0 dB, the antenna is said to be circular polarized. If theaxial ratio is greater than 1-2 dB, the polarization is often referred to as elliptical.

In a circular polarized antenna, the plane of polarization rotates in a circle making onecomplete revolution during one period of the wave.

If the rotation is clockwise looking in the direction of propagation, the sense iscalled right-hand-circular (RHC).

If the rotation is counterclockwise, the sense is called left-hand-circular (LHC).

Antennas

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Polarization (continued)

An antenna is said to be vertically polarized (linear) when its electric field isperpendicular to the Earth's surface.

An example of a vertical antenna is a broadcast tower for AM radio or the "whip"antenna on an automobile.

Horizontally polarized (linear) antennas have their electric field parallel to the Earth'ssurface.

Television transmissions in the USA use horizontal polarization.

Maximum signal strength between stations occurs when both stations are using

identical polarization. In a linearly polarized system, a misalignment of polarization of 45 degrees will

degrade the signal up to 3 dB and if misaligned 90 degrees the attenuation can be 20dB or more.

Likewise, in a circular polarized system, both antennas must have the same sense. If

not, an additional loss of 20 dB or more will be incurred. Also note that linearly polarized antennas will work with circularly polarized antennas

and vice versa. However, there will be up to a 3 dB loss in signal strength.

Circular polarization is most often used for satellite communications.

Antennas

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Transmission lines are a very important part of a communications system.

They carry RF signals from one place to another.

Transmission lines are used to interconnect antennas and receivers/transmitters, andinterconnect computers in a network.

The flow of RF through a transmission line is very different from the flow of DC along apair of wires.

It is possible for a transmission line that is open-circuited at one end to look like a shortcircuit at the other end and in general, the impedance one measures at the input of atransmission line is dependent not only on the load placed at the far end of the line, butalso on the electrical length of the line.

It is these unusual properties that make transmission lines more than just a pair of wires.

Transmission Lines

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Types of transmission lines:

The simplest type of transmission line consists of two conductorsseparated by a small distance. This type of transmission line iscalled parallel line, open wire line, or ladder line.

Another type of two wire transmission line consists of two parallelwires embedded in an insulating material (typically polyethylene).This type of transmission line is called twin-lead, and is verysimilar to open wire line.

Another type of two wire line is called unshielded twisted pair.(UTP). It consists of two wires twisted around one another. Themost common type of UTP is CAT5 network cable. It consists of4 UTPs in a common sheath.

A fourth type of transmission line is shielded pair. It consists oftwo conductors insulated from each other and surrounded by a

shield made of metal braid. The braided shield prevents RF frombeing radiated by the conductors as well as stray RF fromentering the transmission line.

Transmission Lines

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Types of transmission lines (continued):

A fifth type is coaxial cable (coax). A coaxial cable consists of

two conductors separated by a dielectric material. The center

conductor and the outer conductor, or shield, are configured in

such a way that they form concentric cylinders with a commonaxis (hence co-axial).

Yet another type of transmission line is a hollow metal tube,

known as waveguide.

In a waveguide the RF travels as a guided electromagneticwave, rather than as RF current, as is the case for the

other types of transmission lines.

The dimensions of the waveguide must be on the order of

one wavelength of the guided RF wave, which limits

application of waveguides to frequencies in the UHF andmicrowave region.

Transmission Lines

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Flexible (Braided) Coaxial Cable is by far the most common type of closed transmissionline because of its flexibility.

This type of cable is used in practically all applications requiring complete shielding ofthe center conductor.

The effectiveness of the shielding depends upon the weave of the braid and thenumber of braid layers.

One of the draw-backs of braided cable is that the shielding is not 100% effective,especially at higher frequencies. This is because the braided construction can permitsmall amounts of short wavelength (high frequency) energy to radiate.

Normally this does not present a problem; however, if a higher degree of shielding isrequired, semi-rigid coaxial cable is recommended.

In some high frequency flexible coaxial cables the outer shield consists if normalbraids and an extra aluminum foil shield to give better high frequency shielding.

Semi-rigid Coaxial Cable uses a solid tubular outer conductor, so that all the RF energy iscontained within the cable. For applications using frequencies higher than 30 GHz aminiature semi-rigid cable is recommended.

Transmission Lines

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In communication and information processing, a transmitter is any object (source) whichsends information to an observer (receiver).

In radio electronics and broadcasting, a transmitter usually has an oscillator, amodulator, and amplifiers.


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A crystal oscillatoris generally used because of its ability to provide a very stablereference for generating the transmitters signal.

The oscillator is then multiplied up to the desired transmit frequency.

The signal then gets modulated by commands or data. The information is either modulated directly onto the transmit signal (called the

carrier) or it is first modulated on a subcarrier and then onto the transmit signal.

For the transmit signal to be at a sufficient level the final stage of the transmitter is anamplifier.


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There are several modulation methods used.

Analog modulation

Amplitude Modulation (AM): AM works by varying the strength of the transmittedsignal in relation to the information being sent.

Single-Sideband (SSB): A refinement of amplitude modulation that more efficientlyuses electrical power and bandwidth.

Frequency Modulation (FM): Conveys information over a carrier wave by varying itsfrequency. The instantaneous frequency of the carrier is directly proportional to theinstantaneous value of the input signal.

Phase Modulation (PM): Represents information as variations in the instantaneous

phase of a carrier wave. It tends to require more complex receiving hardware andthere can be ambiguity problems in determining whether, for example, the signal haschanged phase by +180 or -180.

Space Modulation (SM): This modulation method differs from internal modulationmethods inside most other radio transmitters in that the phases and powers of twoindividual signals mix within airspace, rather than in a modulator.


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Digital Modulation On-off Keying (OOK): Represents digital data as the presence or absence of a carrier

wave.

Frequency Shift Keying (FSK): Digital information is transmitted through discretefrequency changes of a carrier wave. With this scheme, the "1" is called the mark

frequency and the "0" is called the space frequency. Amplitude Shift Keying (ASK): Represents digital data as variations in the amplitude

of a carrier wave.

Phase Shift Keying (PSK): Conveys data by changing, or modulating, the phase of areference signal (the carrier wave).

Various forms of PSK are:

DPSK: Differential Phase Shift Keying

BPSK: Binary Phase Shift Keying

QPSK: Quadrature Phase Shift Keying

OQPSK: Offset Quadrature Phase Shift Keying

Quadrature Amplitude Modulation (QAM): Conveys data by changing (modulating)the amplitude of two carrier waves. These two waves, usually sinusoids, are out ofphase with each other by 90 and are thus called quadrature carriers.


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Spread Spectrum

Frequency Hopping Spread Spectrum (FHSS): A method of transmitting radio signalsby rapidly switching a carrier among many frequency channels, using apseudorandom sequence known to both transmitter and receiver.

Direct Sequence Spread Spectrum (DSSS): Phase modulation of a sine wave with acontinuous string of pseudo-noise (PN) code symbols called "chips", each of whichhas a much shorter duration than an information bit.

That is, each information bit is modulated by a sequence of much faster chips.Therefore, the chip rate is much higher than the information bit rate.

It uses a signal structure in which the sequence of chips produced by thetransmitter is known a prioriby the receiver.

The receiver can then use the same PN sequence to counteract the effect of thePN sequence on the received signal in order to reconstruct the information

signal.


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An amplifier, or simply amp, is any device that changes, usually increases, the amplitudeof a signal.

Some types of Amplifiers:

Power Amplifier (PA): In general a power amplifier is designated as the last

amplifier in a transmission chain (the output stage). Types of PAs:

Solid State Power Amp (SSPA) Is the most common used because of itscompact size.

Traveling-Wave Tube Amplifier (TWTA) is an electronic device used to amplifyradio frequency signals to high power. The bandwidth of a broadband TWT canbe as high as three octaves, although tuned (narrowband) versions exist, andoperating frequencies range from 300 MHz to 50 GHz.

Klystron is a specialized linear-beam vacuum tube (evacuated electron tube).Klystrons are used as amplifiers at microwave and radio frequencies to producehigh-power carrier waves for space communications.

Low Noise Amplifier (LNA): This is generally the first amplification of a receivedsignal from the antenna.

Amplifiers

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Figures of merit: The quality of an amplifier can be characterized by a number ofspecifications, provided below.

Gain: The gain of an amplifier is the ratio of output to input power or amplitude, and isusually measured in decibels. (When measured in decibels it is logarithmically relatedto the power ratio: G(dB)=10 log(Pout/Pin)).

Bandwidth: The bandwidth (BW) of an amplifier is the range of frequencies for whichthe amplifier gives "satisfactory performance". Bandwidth can be defined as thedifference between the lower and upper half power points, also known as the 3 dBbandwidth. Bandwidths for other response tolerances are sometimes quoted (1 dB,6 dB etc.).

Efficiency:A measure of how much of the DC input power is usefully applied to the

amplifier's output. Class A amplifiers are very inefficient, in the range of 1020% with a max

efficiency of 25%.

Class B amplifiers have a very high efficiency but are impractical because of highlevels of distortion. In practical design, the result of a tradeoff is the class AB

design. Class AB amplifiers are commonly between 3555% efficient with a theoretical

maximum of 78.5%.

Amplifiers

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Efficiency (continued):

Class D switching amplifiers have reported efficiencies as high as 97%.

The efficiency of the amplifier, limits the amount of total power output that isusefully available.

Note that more efficient amplifiers run much cooler, and often do not need anycooling fans even in multi-kilowatt designs. The reason for this is that the loss ofefficiency produces heat as a by-product of the energy lost during the conversionof power. In more efficient amplifiers there is less loss of energy so in turn lessheat.

Linearity:An ideal amplifier would be a totally linear device, but real amplifiers are

only linear within certain practical limits.

Noise: This is a measure of how much noise is introduced in the amplificationprocess.

Output dynamic range: Usually given in dB, between the smallest and largest usefuloutput levels. The lowest useful level is limited by output noise, while the largest is

limited most often by distortion. The ratio of these two is quoted as the amplifierdynamic range. More precisely, ifS = maximal allowed signal power and N= noisepower, the dynamic range DRis DR = (S + N ) /N.

Slew rate: The maximum rate of change of output , usually quoted in volts persecond (or microsecond).

Amplifiers

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A radio receiveris an electronic circuit that receives its input from an antenna, useselectronic filters to separate a wanted radio signal from all other signals picked up by thisantenna, amplifies it to a level suitable for further processing, and finally converts throughdemodulation and decoding the signal into a form usable for the consumer, such assound, pictures, digital data, measurement values, navigational positions, etc.

LNA

IFA

Receivers

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Basic Receiver Characteristics

Sensitivity: The measure of receivers ability to reproduce very weak signals.

The weaker the signal that can be applied and still produce a certain signal-to-

noise (S/N) ratio, the better that receivers sensitivity rating.

Usually, sensitivity is specified as the signal strength in microvolts necessary to

cause a S/N of 10 dB, or 3.16:1.

Selectivity: Determines the extent to which the receiver is capable of distinguishing

between the desired signal and the undesired signals.

This is achieved by using high performance filters.

Noise: Noise is the limiting factor on the minimum usable signal that the receiver

can process and still produce a usable output.

Expressed in decibels, it is an indication of the degree to which a circuit deviatesfrom the ideal.

A noise figure of 0 decibels is ideal.

Receivers

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Types of Receivers:

Basically there is one type of receiver: the superheterodyne.

The process of mixing the received signal is called heterodyning and if the local

oscillator selected is above the received signal the system is referred to as a

superheterodyne receiver.

The advantage of this system is the only part requiring change for receiving a

signal at a different frequency (within the operating band) is the local oscillatorused in the down conversion.

So FM, AM, CW, PSK, BPSK, QPSK, etc signals are received using a

superheterodyne receiver as the core. Additional electronics are needed to recover

the information being transmitted.

Receivers

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D i ti f B i RF t t i t


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Signal Generators

A signal generator, also known variously as a test signal generator, functiongenerator, tone generator, arbitrary waveform generator, digital pattern generator orfrequency generator is an electronic device that generates repeating or non-repeatingelectronic signals (in either the analog or digital domains). They are generally used in

designing, testing, troubleshooting, and repairing electronic devices.. There are many different types of signal generators, with different purposes and

applications (and at varying levels of expense).

In general, no device is suitable for all possible applications.

Generators as a Continuous Wave (CW) source are often used as local oscillators inthe development or testing of transmitters and receivers.

Used in a swept mode frequency responses of many devices, such as amplifiers,filters, and mixers can be measured.

Description of Basic RF test equipment

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D i ti f RF t t i t


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Spectrum Analyzer

The spectrum analyzer, like an oscilloscope, is a basic tool used for observing

signals. Where the oscilloscope provides a window into the time domain, the

spectrum analyzer provides a window into the frequency domain.

Description of RF test equipment

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Description of RF test eq ipment


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Spectrum Analyzer (continued)

The spectrum analyzer settings must be wisely set for application-specificmeasurements, and the measurement procedure optimized to take best advantage ofthe specifications.

The resolution bandwidth (RBW) setting must be considered when concerned withseparating spectral components, setting an appropriate noise floor and demodulatinga signal.

Before making any measurement, it is important to know that there are severaltechniques that can be used to improve both amplitude and frequency measurement

accuracies. A spectrum analyzers ability to measure low-level signals is limited by the noise

generated inside the spectrum analyzer. This sensitivity to low-level signals isaffected by the analyzer settings.

Total measurement uncertainty involves adding up the different sources ofuncertainty in the spectrum analyzer. If any controls can be left unchanged such asthe RF attenuator setting, resolution bandwidth, or reference level, all uncertaintiesassociated with changing these controls drop out, and the total measurementuncertainty is minimized.


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Power Meter

Power measurement is the fundamental parameter for characterizing components

and systems at RF and microwave frequencies.

Above the range of 30 MHz to 100 MHz, where the parameters of voltage and currentbecome inconvenient or more difficult to measure, microwave power becomes the

parameter of choice.

Power specifications are often the critical factor in the design, and ultimately the

performance, of almost all RF and microwave equipment.


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Counters

The conventional counter is a digital electronic device which measures the frequency

of an input signal. It may also have been designed to perform related basic

measurements including the period of the input signal, ratio of the frequency of twoinput signals, time interval between two events and totalizing a specific group of

events.


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Basic RF Equations


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A link budget commonly refers to the complete gain and loss equation from the

transmitter, through the ambient medium (air, cable, waveguide, fiber, etc.) and through

to the receiver.

Although the complete equation would incorporate many terms, the high-level block

diagram shown below is often used.

Prx = Ptx + Gtx + Grx - Afs Am; Where

Prx = received power at detector ( dBW )

Ptx = transmitter output power ( dBW )

Gtx = transmitter antenna gain ( dBi )

Grx = receiver antenna gain ( dBi )

Afs = free space attenuation ( dB )

Am = miscellaneous attenuation ( radome, rain, etc. )

Basic RF Equations

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Basic RF Equations


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As the transmitted signal traverses the atmosphere its power level changes at a rate

inversely proportional to the distance traveled. The formula above accounts for only the

diminishing voltage without accounting for absorption or dispersion by the atmosphere.

As an example, an uplink signal of 2106.40625 MHz transmitted 300 KM (a typical shuttle

altitude) would experience a loss of 148.46 dB.

=c/f: where c (speed of light) = 2.99792458 x 108m/sec

=0.142324 meters

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Cable attenuation is the sum of the conductor losses and the dielectric losses per thefollowing equations.

d = outside diameter of inner conductor in mm.

D = inside diameter of outer conductor in mm.

er=relative dielectric constant.

f =frequency in GHz.

Prd =inner conductor material resistivity relative to copper. PrD =outer conductor material resistivity relative to copper.

=skin depth

Typical losses for commonly used 50 ohm double shielded cables at 2.1 GHz.

RG174 1.33 dB/m

RG214 0.37 dB/m

RG223 0.66 dB/m RG400 0.72 dB/m

LMR240 0.39 dB/m

LMR600 0.13 dB/m

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The antenna gain G (dBi), is related to its diameter d (m), by the following equation, where

=wavelength

=antenna efficiency (1); typically 0.5

f=frequency in Hz

c=speed of light (2.99792458 x 108 m/sec

d=the dish diameter

For a dish with diameter 11 meters at 210640625 Hz its gain is 44.69 dBi

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Often the noise figure (NF) of a device is specified at a specific temperature (e.g. 20C)because the NF goes up as the temperature goes up in a non-linear fashion.

For example, what is the NF of an amplifier at 85C, having a nf of 2.0 dB at 20C.

NF = 10Log[10 (nf/10) 1 + (Te/To)]; where

NF = Noise Figure

nf = Noise Figure at 20C

Te = Operating Temperature in kelvins

To = Ambient temperature in kelvins

K = C + 273

NF = 10Log[1.58 1 + 358/293]

NF = 10Log[1.80] = 2.56 dB Often received signal strength is specified in dBm. But sometimes it is specified in dB-Hz.

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If the NF of the receiver is known, conversion is fairly simple.

Receiver Temperature (TR)=293(10(NF/10)-1) = 171.37K, for a NF of 2.0

System Temperature (TS)= TR+ TO = 171.37 + 293 = 464.37K

System Noise Density (NO)= -198.6dB/Hz + 10Log (TS) = -171.93 = -172 dBm/Hz

For a received level of 33 dB-Hz, the converted value in dBm is 33-172 = -139 dBm

-198.6 comes from Boltzmann's constant expressed in dB: 10Log(1.3806503 x 10-23)+30

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USEFUL WEB SITES


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http://www.rfcafe.com

Provides many helpful formulas and resources

http://www.timesmicrowave.com/cable_calculators/

Cable performance calculators

http://www.home.agilent.com Go to technical support application notes test and measurements RF and

Microwave

Hundreds of applications on how to use various types of equipment to make specific

RF measurements.

References: Principles of Communication Systems by Taub and Schilling 1971

Handbook of Electronic Calculations Edited by Kaufman and Seidman 1979

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LAB DEMONSTRATION


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Typical bench level test on a transponder.

Display of different modulation spectrums.

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Documents

RF Training Module PDF