T7C-2014: Antenna measurements and troubleshooting: measuring SWR; dummy loads; coaxial cables; feed line failure modes
What is the primary purpose of a dummy load?
To prevent the radiation of signals when making tests
To prevent over-modulation of your transmitter
To improve the radiation from your antenna
To improve the signal to noise ratio of your receiver
Which of the following instruments can be used to determine if an antenna is resonant at the desired operating frequency?
An antenna analyzer
A Q meter
A frequency counter
What, in general terms, is standing wave ratio (SWR)?
A measure of how well a load is matched to a transmission line
The ratio of high to low impedance in a feed line
The transmitter efficiency ratio
An indication of the quality of your station’s ground connection
What reading on an SWR meter indicates a perfect impedance match between the antenna and the feed line?
1 to 1
2 to 1
1 to 3
10 to 1
What is the approximate SWR value above which the protection circuits in most solid-state transmitters begin to reduce transmitter power?
2 to 1
1 to 2
6 to 1
10 to 1
What does an SWR reading of 4:1 indicate?
Loss of -4dB
Good impedance match
Gain of +4dB
What happens to power lost in a feed line?
It is converted into heat
It increases the SWR
It comes back into your transmitter and could cause damage
It can cause distortion of your signal
What instrument other than an SWR meter could you use to determine if a feed line and antenna are properly matched?
Which of the following is the most common cause for failure of coaxial cables?
The velocity factor exceeds 1.0
Why should the outer jacket of coaxial cable be resistant to ultraviolet light?
Ultraviolet light can damage the jacket and allow water to enter the cable
Ultraviolet resistant jackets prevent harmonic radiation
Ultraviolet light can increase losses in the cable’s jacket
Ultraviolet and RF signals can mix together, causing interference
What is a disadvantage of air core coaxial cable when compared to foam or solid dielectric types?
It requires special techniques to prevent water absorption
It has more loss per foot
It cannot be used for VHF or UHF antennas
It cannot be used at below freezing temperatures
Which of the following is a common use of coaxial cable?
Carrying RF signals between a radio and antenna
Carrying dc power from a vehicle battery to a mobile radio
Securing masts, tubing, and other cylindrical objects on towers
Connecting data signals from a TNC to a computer
What does a dummy load consist of?
A non-inductive resistor and a heat sink
A high-gain amplifier and a TR switch
A low voltage power supply and a DC relay
A 50 ohm reactance used to terminate a transmission line
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