Tags: none

A Gamma-match can match impedance below 50 ohms right up to that 50 ohms which your transceiver wants to see. A Yagi antenna almost never has an impedance of 50 ohms.

REF: http://www.dx-antennas.com/Gamma_match.htm

Last edited by kb1cxd. Register to edit

Tags: none

Memorization trick: a SECTION of transmission line = a STUB (like a movie ticket stub is a section of the ticket)

In microwave and radio-frequency engineering, a stub is a length of transmission line or waveguide that is connected at one end only. The free end of the stub is either left open-circuit or (especially in the case of waveguides) short-circuited. Neglecting transmission line losses, the input impedance of the stub is purely reactive; either capacitive or inductive, depending on the electrical length of the stub, and on whether it is open or short circuit. Stubs may thus be considered to be frequency-dependent capacitors and frequency-dependent inductors. Because stubs take on reactive properties as a function of their electrical length, stubs are most common in UHF or microwave circuits where the line lengths are more manageable. Stubs are commonly used in antenna impedance matching circuits and frequency selective filters.

http://en.wikipedia.org/wiki/Stub_(electronics)

Last edited by ldwyze. Register to edit

Tags: none

The PVC insulation that encases the center conductor of a coaxial cable is within the outer tube that provides a series capacitance of some gamma-type matching networks.
The inductive reactance is cancelled by the series capacitance within the matching network. This will lead to a defined resonance.

Hint: "Matching Network" is in the answer.

Last edited by kd7bbc. Register to edit

Tags: none

Tags: none

When implementing a quarter-wave Q-section (also called a quarter wave impedance transformer), the impedance \(Z_o\) of the quarter wave section should be equal to \(\sqrt{Z_{in} Z_L}\). In this case: \(Z_o = \sqrt{50 * 100} = 70.71 \Omega\), which is closest to 75 ohms.

Last edited by zulud9. Register to edit

Tags: none

The reflection coefficient is defined as

\[\Gamma = {(Z_L - Z_0) \over (Z_L + Z_0)}\]

where \(Z_L\) is the impedance of the load and \(Z_0\) is the characteristic impedance of the transmission line. If \(Z_0\) and \(Z_L\) are the same, the reflection coefficient (\(\Gamma\)) is zero. And the reflection coefficient increases the more \(Z_L\) and \(Z_0\) differ, indicating stronger mismatch between the load and transmission line.

Last edited by kv0a. Register to edit

Tags: none

A WIlkinson Power Divider is used in microwave circuitry to split the power coming into the divider's input port into two output ports. Each port has the same impedance and the two output ports are of equal power and are isolated from each other, which minimizes crosstalk between ports. The Wilkinson Divider is passive, so it works equally well as a power combiner due to reciprocity.

Hint: it divides the power "50/50" between two 50 ohm loads.

Last edited by nimbius. Register to edit

Tags: none

The gamma match is an effective method of connecting a 50-ohm coaxial cable feed line to a grounded tower so it can be used as a vertical antenna.

The gamma match is the name of an antenna matching system that matches an unbalanced feed line to an antenna by feeding the driven element both at the center of the element and at a fraction of a wavelength to one side of center.

Mnemonic: A Grounded tower needs a Gamma match.

Last edited by kd7bbc. Register to edit

Tags: none

Tags: none