Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives Magazine Sponsor RF Cafe Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Alliance Test Equipment Centric RF Empower RF ISOTEC Reactel RF Connector Technology San Francisco Circuits Anritsu Amplifier Solutions Anatech Electronics Axiom Test Equipment Berkeley Nucleonics Conduct RF Copper Mountain Technologies everything RF Exodus Advanced Communications Innovative Power Products KR Filters LadyBug Technologies PCB Directory Rigol TotalTemp Technologies Werbel Microwave Windfreak Technologies Wireless Telecom Group Withwave Sponsorship Rates RF Cafe Software Resources Vintage Magazines RF Cafe Software WhoIs entry for RF Cafe.com Thank you for visiting RF Cafe!
Exodus Advanced Communications Best in Class RF Amplifier SSPAs

RF Electronics Shapes, Stencils for Office, Visio by RF Cafe

Axiom Test Equipment - RF Cafe

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

RF Cascade Workbook for Excel

RF & Electronics Symbols for Visio

RF & Electronics Symbols for Office

RF & Electronics Stencils for Visio

RF Workbench  (shareware)

T-Shirts, Mugs, Cups, Ball Caps, Mouse Pads

These Are Available for Free

Espresso Engineering Workbook™

Smith Chart™ for Excel

Copper Mountain Technologies (VNA) - RF Cafe

Module 21 - Test Methods and Practices
Navy Electricity and Electronics Training Series (NEETS)
Chapter 5:  Pages 5-11 through 5-20

Module 21 − Test Methods and Practices

Pages i , 1−1, 1−11, 1−21, 2−1, 2−11, 2−21, 2−31, 2−41, 3−1, 3−11, 3−21, 3−31, 4−1, 4−11, 5−1, 5−11, 5−21, 5−31, AI−1 to AI−3, Index



Time versus frequencies - RF Cafe

Figure 5-8C. - Time versus frequencies.




The frequency domain contains information not found in the time domain. The spectrum analyzer can display signals composed of more than one frequency (complex signals). It can also discriminate between the components of the signal and measure the power level at each one. It is more sensitive to low-level distortion than an oscilloscope. Its sensitivity and wide, dynamic range are also useful for measuring low-level modulation, as illustrated in views a and B of figure 5-9. The spectrum analyzer is useful in the measurement of long- and short-term stability such as noise sidebands of an oscillator, residual fm of a signal generator, or frequency drift of a device during warm-up, as shown in views A, B, and C of figure 5-10.


Examples of time-domain (left) and frequency-domain (right) low-level signals - RF Cafe

Figure 5-9A. - Examples of time-domain (left) and frequency-domain (right) low-level signals.




Examples of time-domain (left) and frequency-domain (right) low-level signals - RF Cafe

 Figure 5-9B. - Examples of time-domain (left) and frequency-domain (right) low-level signals.


Spectrum analyzer stability measurements - RF Cafe

Figure 5-10A. - Spectrum analyzer stability measurements.




Spectrum analyzer stability measurements - RF Cafe

 Figure 5-10B. - Spectrum analyzer stability measurements.


Spectrum analyzer stability measurements - RF Cafe

Figure 5-10C. - Spectrum analyzer stability measurements.

The swept-frequency response of a filter or amplifier and the swept-distortion measurement of a tuned oscillator are also measurable with the aid of a spectrum analyzer. However, in The Course of these measurements, a variable persistence display or an X-Y recorder should be used to simplify readability. Examples of tuned-oscillator harmonics and filter response are illustrated in figure 5-11. Frequency- conversion devices such as mixers and harmonic generators are easily characterized by such parameters as conversion loss, isolation, and distortion. These parameters can be displayed, as shown in figure 5-12, with the aid of a spectrum analyzer.





Swept-distortion and response characteristics - RF Cafe

Figure 5-11. - Swept-distortion and response characteristics.


Frequency-conversion characteristics - RF Cafe

Figure 5-12. - Frequency-conversion characteristics.



Present-day spectrum analyzers can measure segments of the frequency spectra from 0 hertz to as high as 300 gigahertz when used with waveguide mixers.




Figure 5-13 shows a typical spectrum analyzer. The previously mentioned measurement capabilities can be seen with a spectrum analyzer. However, you will find that the spectrum analyzer generally is used to measure spectral purity of multiplex signals, percentage of modulation of AM signals, and modulation characteristics of fm and pulse-modulated signals. The spectrum analyzer is also used to interpret the displayed spectra of pulsed RF emitted from a radar transmitter.


Typical spectrum analyzer - RF Cafe

Figure 5-13. - Typical spectrum analyzer.




Complex waveforms are divided into two groups, PERIODIC WAVES and NONPERIODIC WAVES. Periodic waves contain the fundamental frequency and its related harmonics. Nonperiodic waves contain a continuous band of frequencies resulting from the repetition period of the fundamental frequency approaching infinity and thereby creating a continuous frequency spectrum.




In all types of modulation, the carrier is varied in proportion to the instantaneous variations of the modulating waveform. The two basic properties of the carrier available for modulation are the Amplitude Characteristic and ANGULAR (frequency or phase) Characteristic.


Amplitude Modulation


The modulation energy in an amplitude-modulated wave is contained entirely within the sidebands. Amplitude modulation of a sinusoidal carrier by another sine wave would be displayed as shown in figure 5-14. For 100% modulation, the total sideband power would be one-half of the carrier power; therefore,




each sideband would be 6 dB less than the carrier, or one-fourth of the power of the carrier. Since the carrier component is not changed with AM transmission, the total power in the 100-percent-modulated wave is 50% higher than in the unmodulated carrier. The primary advantage of the log display that is provided by the spectrum analyzer over the linear display provided by the oscilloscopes for percentage of modulation measurements is that the high dynamic range of the spectrum analyzer (up to 70 dB) allows accurate measurements of values as low as 0.06%. It also allows the measurements of low-level distortion of AM signals. Both capabilities are illustrated in figure 5-15, view A, view B, and view C. The chart in figure 5-16 provides an easy conversion of dB down from carrier into percentage of modulation.


Spectrum analyzer display of an AM signal - RF Cafe

Figure 5-14. - Spectrum analyzer display of an AM signal.


Spectrum analyzer displays of AM signals - RF Cafe

Figure 5-15A. - Spectrum analyzer displays of AM signals.




Spectrum analyzer displays of AM signals - RF Cafe

Figure 5-15B. - Spectrum analyzer displays of AM signals.


Spectrum analyzer displays of AM signals - RF Cafe

Figure 5-15C. - Spectrum analyzer displays of AM signals.




Modulation percentage versus sideband levels - RF Cafe

Figure 5-16. - Modulation percentage versus sideband levels.


Note: Anything greater than -6 dB exceeds 100% modulation and produces distortion, as shown in figure 5-16.


In modern, long-range HF communications, the most important form of amplitude modulation is SSB (single-sideband). In SSB either the upper or lower sideband is transmitted, and the carrier is suppressed. SSB requires only one-sixth of the output power required by AM to transmit an equal amount of intelligence power and less than half the bandwidth. Figure 5-17 shows the effects of balancing the carrier of an AM signal. The most common distortion experienced in SSB is intermodulation distortion, which is caused by nonlinear mixing of intelligence signals. The two-tone test is used to determine if any intermodulation distortion exists. Figure 5-18 illustrates the spectrum analyzer display of the two-tone test with the modulation applied to the upper sideband input.


Double sideband carrier suppressed - RF Cafe

Figure 5-17. - Double sideband carrier suppressed.




Two-tone test - RF Cafe

Figure 5-18. - Two-tone test.


Q-5.    What is the advantage of single-sideband (SSB) transmission over AM transmission?


Frequency Modulation


In frequency modulation, the instantaneous frequency of the radio-frequency wave varies with the modulation signal. As mentioned in NEETS, module 12, the amplitude is kept constant. The number of times per second that the instantaneous frequency varies from the average (carrier frequency) is controlled by the frequency of the modulating signal. The amount by which the frequency departs from the average is controlled by the amplitude of the modulating signal. This variation is referred to as the Frequency DEVIATION of the frequency-modulated wave. We can now establish two clear-cut rules for frequency deviation rate and amplitude in frequency modulation:


·  Amount of frequency shift is proportional to the amplitude of the modulating signal.


(This rule simply means that if a 10-volt signal causes a frequency shift of 20 kilohertz, then a 20- volt signal will cause a frequency shift of 40 kilohertz.)

·  Rate of frequency shift is proportional to the frequency of the modulating signal.


(This second rule means that if the carrier is modulated with a 1-kilohertz tone, then the carrier is changing frequency 1,000 times each second.)


The amplitude and frequency of the signal used to modulate the carrier will determine both the number of significant sidebands (shown in fig. 5-19) and the amplitude of the sidebands (shown in fig. 5- 20). Both the number of significant sidebands and the bandwidth increase as the frequency of the modulating signal increases.





Distribution of sidebands - RF Cafe

Figure 5-19. - Distribution of sidebands.


Spectrum distribution for a modulation index of 2 - RF Cafe

Figure 5-20. - Spectrum distribution for a modulation index of 2.


NEETS, module 12, should be consulted for an in-depth discussion of frequency-modulation principles.


Q-6.    What happens to an fm signal as you increase the frequency of the modulating signal?




An ideal pulsed radar signal is made up of a train of RF pulses with a constant repetition rate, constant pulse width and shape, and constant amplitude. To receive the energy reflected from a target, the radar receiver requires almost ideal pulse radar emission characteristics. By observing the spectra of a pulsed radar signal, you can easily and accurately measure such characteristics as pulse width, duty cycle, and




NEETS Modules
- Matter, Energy, and Direct Current
- Alternating Current and Transformers
- Circuit Protection, Control, and Measurement
- Electrical Conductors, Wiring Techniques, and Schematic Reading
- Generators and Motors
- Electronic Emission, Tubes, and Power Supplies
- Solid-State Devices and Power Supplies
- Amplifiers
- Wave-Generation and Wave-Shaping Circuits
- Wave Propagation, Transmission Lines, and Antennas
- Microwave Principles
- Modulation Principles
- Introduction to Number Systems and Logic Circuits
- - Introduction to Microelectronics
- Principles of Synchros, Servos, and Gyros
- Introduction to Test Equipment
- Radio-Frequency Communications Principles
- Radar Principles
- The Technician's Handbook, Master Glossary
- Test Methods and Practices
- Introduction to Digital Computers
- Magnetic Recording
- Introduction to Fiber Optics
Note: Navy Electricity and Electronics Training Series (NEETS) content is U.S. Navy property in the public domain.

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024


    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

Copyright  1996 - 2026

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website: AirplanesAndRockets.com

My Daughter's Website: EquineKingdom

RF Cascade Workbook 2018 by RF Cafe

LadyBug RF Power Sensors

Innovative Power Products Passive RF Products - RF Cafe