300 QUESTION BOARD EXAM REVIEWER PART2 Flashcards
- If the SWR is infinite, what type of load does the transmission line has?
Purely reactive
- The standard analog telephone channel bandwidth.
300 – 3400 Hz
- Telephone channel has a band-pass characteristic occupying the frequency range of?
300 – 3400Hz
- Short Circuit Stubs are preferred to open circuit stubs because the latter are?
Liable to radiate
- What is the ratio of the reflected voltage to the incident voltage?
Reflected voltage
- One method of determining antenna impedance?
Quarter wave matching
- Coaxial cable impedance is typically _____.
50-75 ohms
- Waveguides become compulsory above what frequencies?
Above 3 GHz
- Nominal voice channel bandwidth is _____.
4kHz (Nominal is like in name only, actual is 300-3700Hz)
- Quarter-wavelength line is used as _____.
Impedance transformer
- The transmission lines which can convey electromagnetic waves only in higher modes is usually called _____.
Waveguide
- Why is nitrogen gas sometimes used in waveguide?
To keep the waveguide dry
- The apparent speed of propagation along a waveguide based on the distance between wavefronts along the walls of the guide is called?
Phase velocity
A quarter-wave line is connected to an RF generator and is shorted out at the far end. What is the input impedance to the line generator?
A high value of resistance
If the SWR on a transmission line has a high value, the reason could be?
An impedance mismatch between line and load
If a quarter-wave transmission line is shorted at one end…
The line behaves as a parallel-tuned circuit.
A 50-ohm transmission line is feeding an antenna which represents a 50-ohm resistive load. To shorten the line, the length must be?
Any convenient value
The outer conductor of the coaxial cable is usually grounded at?
The beginning and the end of the cable.
A feature of an infinite transmission line is that? Its input impedance at the generator is _____ line’s surge impedance
equal to
When the Surge impedance of a line is matched to a load, the line will?
Transfer maximum power to the load
Other terminology for Characteristic Impedance
Surge Impedance
A lossless line is terminated by a resistive load which is not equal to the surge impedance. If the value of reflection is 0.5, the VSWR is?
3
Ratio of the mismatch between the antenna and the transmitter?
SWR
Commonly used telephone wire?
AWG #19
Distance travelled by a wave in one cycle?
Wavelength
The velocity factor is inversely proportional with respect to the?
square root of the dielectric constant
____ is a hollow structure that has no center conductor, but allows waves to propagate down its length.
Waveguide
To connect a coaxial line to parallel wire line, _____ is used.
Balun (coaxial is unbalanced, parallel is balanced)
In a waveguide, _____ is a specific configuration of electric and magnetic fields that allows a wave to propagate.
Mode
_____ are transmission lines which can convey electromagnetic waves in higher order modes
Waveguide
The twists in twisted wire pairs do what?
It reduces electromagnetic interference
What is the most commonly used transmission line for high frequency applications?
Coaxial
Loading means the addition of?
Inductance
The characteristics of a transmission line does not depend on what? length, conductor diameter, conductor spacing, dielectric material.
Length (Very important, know that Surge Impedance is not affected by length)
One of the following is not a common transmission line impedance: 50, 75, 120, 300.
120
For maximum absorption of power at the antenna, the relationship between Zo and Zl should be?
Equal
_____ is a pattern of voltage and current variations along a transmission line not terminated in its characteristics impedance.
Standing Waves
What is the desirable SWR on a transmission line?
1 (SWR is from1 to infinity. 1SWR means 0 reflection coefficient, meaning: max power transfer)
A 50 ohm Coax is connected to a 73 ohm antenna. What’s the SWR?
1.46 (73-50/73+50 —- 1+x / 1-x)
What is the most desirable reflection coefficient?
0 (no reflection, all absorbed)
What is the ratio expressing the percentage of incident voltage reflected on a transmission line?
Reflection Coefficient
The minimum voltage along a transmission line is 260V, while the maximum is 390V, the SWR is?
1.5 = [1 + (390-260/390+260) / 1 - (390-260/390+260)]
At very high frequencies, transmission lines act as?
Antennas
One meter is one wavelength at a frequency of?
300MHz (Speed of Light / Frequency = Wavelength)
A shorted quarter-wave line at the operating frequency acts like?
Parallel resonant circuit
A shorted half-wave line at the operating frequency acts like?
Series resonant circuit
A medium least susceptible to noise?
Coaxial
A medium most widely used in LANs?
Twisted Pairs