Answer: The delta matching system
An easy way to remember this is the two lines help form a triangle, or the Greek letter used as the fourth letter in the phonetic alphabet - \(\Delta\).
Last edited by wileyj2956. Register to edit
Tags: arrl chapter 9 arrl module 9e
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: arrl chapter 9 arrl module 9e
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: arrl chapter 9 arrl module 9e
Hint: "Matching Network" is in the answer.
kg5kou
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 in-turn lead to a defined resonance.
-KE0IPR
Last edited by ke0ipr. Register to edit
Tags: arrl chapter 9 arrl module 9e
Think of the hairpin as a coil. It is a conductor with an inductive reactance. A tuned antenna is resonant which means inductive and capacitive reactances cancel each other out. For an inductor to tune an antenna the antenna must be capacitive.
-w1sop-2
Hint: Hairpin = Inductor, Inductors cancel Capacitors, to tune, we must have cancelled reactance. Thus The driven element reactance must be capacitive
-KE0IPR
Last edited by pimusim. Register to edit
Tags: arrl chapter 9 arrl module 9e
The equivalent lumped-constant network for a hairpin matching system of a 3-element Yagi is a shunt inductor.
Remember that the driven element must be capacitive. The hairpin matching system must be inductive. Hence, a shunt inductor is its equivalent.
Last edited by qubit. Register to edit
Tags: arrl chapter 9 arrl module 9e
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: arrl chapter 9 arrl module 9f
Think of logic behind this problem. One ratio number must be higher than the other (it is the whole point of ratios). This is where SWR comes into play. SWR compares the impedance together.
Last edited by finbays. Register to edit
Tags: arrl chapter 9 arrl module 9f
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.
-KE0IPR
Mnemonic: A Grounded tower needs a Gamma match.
Last edited by xxdpplus. Register to edit
Tags: arrl chapter 9 arrl module 9e
The impedance of a quarter wavelength matching transformer can be found by taking the square root of the product of the two impedances to be matched.
For this problem a 100 ohm impedance must be matched to a 50 ohm impedance.
\[\sqrt{50 \times 100}=\sqrt{5000} \approx 70.71\approx75\]
Therefore, a quarter (1/4) wavelength piece of 75-ohm coax should match the two impedances relatively well.
The formula for the impedance of a quarter wavelength matching transformer is: \[Z_{\text{in}}=\frac{Z_0^2}{Z_L}\Rightarrow Z_0=\sqrt{Z_{\text{in}}Z_L}\] where:
\(Z_{\text{in}}\) is the input impedance
\(Z_0\) is the characteristic impedance
\(Z_L\) is the load impedance
Last edited by wileyj2956. Register to edit
Tags: arrl chapter 9 arrl module 9g
Universal stubs are most used in VHF and higher applications to keep the feed line manageable. They are called universal because it can match unknown feed line and antenna impedances.
Last edited by wileyj2956. Register to edit
Tags: arrl chapter 9 arrl module 9e
Memorization trick:
Each band goes on stage in phases at a concert
Also, driven element is mentioned in question and answer
Some beam antennas use multiple driven elements in order to make them multi-band antennas. The primary purpose of a phasing line when used with an antenna having multiple driven elements is that it ensures that each driven element operates in concert with the others to create the desired antenna pattern.
-KE0IPR
Last edited by mrdfox7. Register to edit
Tags: arrl chapter 9 arrl module 9d
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: The correct answer is the only one with the number 50 in it.
Last edited by bearzohmy. Register to edit
Tags: arrl chapter 9 arrl module 9d