AdvancedA-007-003-006
A quarter-wave stub, for use at 15 MHz, is made from a coaxial cable having a velocity factor of 0.8. Its physical length will be:
D
Answer
Interference, EMC, and safety
Type
A
7.5 m (24.6 ft)
B
8 m (26.2 ft)
C
12 m (39.4 ft)
D
4 m (13.1 ft)
Answer Notes
The physical length of a transmission line stub is determined by its electrical length and its velocity factor. First, calculate the full free-space wavelength by dividing the speed of light constant (300) by the frequency (15 MHz), which equals 20 metres.
Since a quarter-wave stub is needed, divide the 20 metres by 4, resulting in a free-space quarter-wavelength of 5 metres. Finally, multiply this by the velocity factor of 0.8 to find the physical length, which is 4 metres (approximately 13.1 feet).
Previous · A-007-003-005
The driven element of a Yagi antenna is connected to a coaxial transmission line. The coax braid is connected to the centre of the driven element and the centre conductor is connected to a variable capacitor in series with an adjustable mechanical arrangement on one side of the driven element. The type of matching is:
Next · A-007-003-007
The matching of a driven element with a single adjustable mechanical and capacitive arrangement is descriptive of: