Book 5 Flashcards
What is the purpose of transmission lines?
To convert RF signal from the transmitter to an aerial and from the aerial to a receiver.
How do you work out Characteristic Impedance?
Characteristic Impedance = Square root of L/C
What is a Non-Resonant Line?
Where the line dissipates all the energy from the line that was supplied by the generator.
What is a Resonant line?
Where some of the energy in a line is not absorbed at the load and will be reflected back towards the generator.
What is a Standing Wave?
When two waves combine at every point along the length of the line to form a resultant, stationary wave.
What is the VSWR of a non-resonant line?
1:1
What VSWR is considered acceptable for radio communication equipment?
2:1
What VSWR is considered unacceptably high?
20:1
What is a Balanced Line?
When both conductors have the same impedances to Earth.
What is an Unbalanced Line?
A transmission line whose conductors have unequal impedances with respect to Earth.
What are the Characteristics of a Co-Axial cable?
- Unbalanced
- Screened
- Flexible
- Insulated
- High power loss
What are the characteristics of Twin Wire Open Feeders?
- Balanced
- High transmitter power output
- Must be clear of the ground at all times
- Practical upper frequency limit is about 100MHz
- Bulky and Rigid
What formulae can be used to calculate wavelength?
Wavelength = C/F
What is Polarisation?
The orientation of the electric field of the radio wave with respect to Earth’s surface.
What is the purpose of the Aerial Tuning Unit?
A device which allows the use of one aerial for a broad range of frequencies or wavelengths.
