Login or Register for FREE!
Subelement E9
ANTENNAS AND TRANSMISSION LINES
Section E9G
The Smith chart
Which of the following can be calculated using a Smith chart?
  • Impedance along transmission lines
  • Radiation resistance
  • Antenna radiation pattern
  • Radio propagation

The Smith chart, invented by Phillip H. Smith (1905-1987),[1][2] is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits.

  1. ^ Smith, P. H.; Transmission Line Calculator; Electronics, Vol. 12, No. 1, pp 29-31, January 1939
  2. ^ Smith, P. H.; An Improved Transmission Line Calculator; Electronics, Vol. 17, No. 1, p 130, January 1944

Last edited by verticalham. Register to edit

Tags: none

What type of coordinate system is used in a Smith chart?
  • Voltage circles and current arcs
  • Resistance circles and reactance arcs
  • Voltage lines and current chords
  • Resistance lines and reactance chords

Smith charts have to do with Impedance matching (Resistance). The coordinate system used is resistance circles, and curves.

Last edited by moogatronic. Register to edit

Tags: none

Which of the following is often determined using a Smith chart?
  • Beam headings and radiation patterns
  • Satellite azimuth and elevation bearings
  • Impedance and SWR values in transmission lines
  • Trigonometric functions

The Smith chart, invented by Phillip H. Smith (1905-1987) http://en.wikipedia.org/wiki/Smith_chart#cite_note-0

http://en.wikipedia.org/wiki/Smith_chart#cite_note-1 is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits.

  1. ^ Smith, P. H.; Transmission Line Calculator; Electronics, Vol. 12, No. 1, pp 29-31, January 1939
  2. ^ Smith, P. H.; An Improved Transmission Line Calculator; Electronics, Vol. 17, No. 1, p 130, January 1944

Transmission lines, and matching circuits have all to do about matching impedence (resistance).

Last edited by ipwnnoobs. Register to edit

Tags: none

What are the two families of circles and arcs that make up a Smith chart?
  • Resistance and voltage
  • Reactance and voltage
  • Resistance and reactance
  • Voltage and impedance

remember: smith chart uses R & R, resistance and reactance.

See wikipedia article for more information

Last edited by kd7bbc. Register to edit

Tags: none

What type of chart is shown in Figure E9-3?
  • Smith chart
  • Free space radiation directivity chart
  • Elevation angle radiation pattern chart
  • Azimuth angle radiation pattern chart

This is a Smith Chart.

The circles, all tangent to each other, represent different resistances. The one closest to the tangent represents an infinite resistance, and the one furthest out (largest circle) represents zero resistance. The curved lines represent reactances, from zero (the straight line) to shorter curved lines, the ones representing larger reactances.

The Smith Chart is used to do antenna calculations by drawing lines rather than using formulas.

Last edited by k6yxh. Register to edit

Tags: none

On the Smith chart shown in Figure E9-3, what is the name for the large outer circle on which the reactance arcs terminate?
  • Prime axis
  • Reactance axis
  • Impedance axis
  • Polar axis

The key word here is "REACTANCE".

Reactance arcs terminate at the "REACTANCE" axis!

Last edited by kd5isa. Register to edit

Tags: none

On the Smith chart shown in Figure E9-3, what is the only straight line shown?
  • The reactance axis
  • The current axis
  • The voltage axis
  • The resistance axis

The straight line (the ONLY straight line) in a Smith Chart is the resistance axis. -K4AGO

Stick trick: The only line that resists bending. - N7ELC

Last edited by kornesque. Register to edit

Tags: none

What is the process of normalization with regard to a Smith chart?
  • Reassigning resistance values with regard to the reactance axis
  • Reassigning reactance values with regard to the resistance axis
  • Reassigning impedance values with regard to the prime center
  • Reassigning prime center with regard to the reactance axis

The Smith chart is plotted on the complex reflection coefficient plane in two dimensions and is scaled in normalised impedance (the most common), normalised admittance or both, using different colours to distinguish between them. These are often known as the Z, Y and YZ Smith charts respectively.[7] Normalised scaling allows the Smith chart to be used for problems involving any characteristic or system impedance which is represented by the center point of the chart. The most commonly used normalization impedance is 50 ohms. Once an answer is obtained through the graphical constructions described below, it is straightforward to convert between normalised impedance (or normalised admittance) and the corresponding unnormalized value by multiplying by the characteristic impedance (admittance). Reflection coefficients can be read directly from the chart as they are unit-less parameters. Wikipedia.org https://en.wikipedia.org/wiki/Smith_chart

Last edited by k4ago. Register to edit

Tags: none

What third family of circles is often added to a Smith chart during the process of solving problems?
  • Standing wave ratio circles
  • Antenna-length circles
  • Coaxial-length circles
  • Radiation-pattern circles

The circles already present on the Smith chart include those for the resistive and reactive components of the normalized load impedance. One would normally use the intersection of these circles to identify the magnitude and angle of gamma, the voltage reflection coefficient.

By maintaining a gamma of constant magnitude about the origin, one can draw a third group of circles. Because standing wave ratio only depends on this magnitude, these circles define the standing wave ratio.

Thus, the correct answer is Standing-wave ratio circles.

Last edited by k4ago. Register to edit

Tags: none

What do the arcs on a Smith chart represent?
  • Frequency
  • SWR
  • Points with constant resistance
  • Points with constant reactance

In the days of slide rules, the Smith chart was packed with lines, curves, grids and nomographs.

The arcs represent points with constant reactance. To interpret impedance on the Smith chart, it is necessary to understand constant resistance circles and constant reactance arcs.

A very comprehensive and in depth depiction of Smith Charts can be found at Wikipedia

Last edited by grinningphd. Register to edit

Tags: none

How are the wavelength scales on a Smith chart calibrated?
  • In fractions of transmission line electrical frequency
  • In fractions of transmission line electrical wavelength
  • In fractions of antenna electrical wavelength
  • In fractions of antenna electrical frequency

The wavelength scales on a Smith chart are calibrated in fractions of transmission line electrical wavelength.


The outer ring of a Smith Chart defines fractional electrical wavelength of feedline starting at zero and ending at 0.5 (half the electrical wavelength). It also defines the direction toward the generator. This is a hint, indicating that this is a feedline length and not antenna length.

Smith Charts are useful to determine feedline line length required to match a load to a radio transmitter.

Last edited by qubit. Register to edit

Tags: none

Go to E9F Go to E9H