4. Feeders & Antennas Flashcards
what are feeders used for?
Connecting the transmitter/receiver to the antenna?
What happens to feeders on transmit and receive?
Feeders exhibit ‘loss’ on transmit & receive.
T/F The longer the cable, the less amount of loss experienced?
FALSE: More loss is experienced the greater the length of the cable.
Why does loss occur?
Loss occurs as some of the RF energy is converted to heat.
What else affects feeder loss?
Frequency.
What kind of feeder is recommended for VHF & UHF ?
Thicker, low-loss feeder cable is recommended.
What are the two types of feeder?
Coaxial & Twin Feeder (Ladder-lined)
Which kind of feeder is more commonly used by amateurs, Coaxial or Ladder Line?
Coaxial.
T/F: Twin Feeder Cable is balanced.
TRUE. Twin Feeder is balanced, Coaxial Cable is unbalanced.
T/F: Twin Feeder has two wires for equal and opposite signals
True. This is why its balanced.
What keeps the signal within coaxial cable?
The Outer braid (screen)
How many types of connector are there?
Four.
What connector is commonly used for HF?
PL259
What is the N Connector commonly used for?
VHF & UHF
What is the one type of connector which is not screw thread locking?
BNC - It is bayonet locking.
What connector is common for handheld radios?
SMA
What Ohm BNC connector is used and why?
50 or 70
50 Ohm - the 75 Ohm is not used as it has a different type of pin.
What do antennas do?
Convert Electrical Signals into Radio Waves (and vice-versa)
T/F: Antennas are designed for specific frequencies.
TRUE. They are also different sizes depending on the band.
In general, Lower Frequencies (Longer Wavelengths) require…..?
Larger Antennas.
Name 3 of the 5 antenna types.
- Yagi
- Dipole
- 5/8 Wave
- 1/4 Wave
- Long Wire
Is a Dipole a balanced or unbalanced antenna?
Balanced.
How long (in Wave Lengths) is a Dipole Antenna?
Half a Wavelength.
How long would a dipole antenna need to be to work in 14Mhz?
14Mhz is the 20 metre band, so 10 metres, as it is half a wavelength long.
What does a Polar Pattern show?
A polar pattern shows how RF signals radiate from the antenna.
Where are Omni-Directional signals directed?
Omni-Directional signals are directed in all directions.
What type of Antenna is Omni - Directional?
Dipole
How long must a 1/4 wave Ground Plane Antenna be to work at 144Mhz (2m Band)
50cm Long
What forms the ground plane on a antenna?
4 Horizontal Wires
What are the 4 horizontal wires are used as the ground planes called?
Radials
What do the radials do?
They form a ground plane which act as a mirror for radio signals.
How long is a 5/8 Wave Ground Plane Antenna?
A 5/8 of a wavelength
Where do you get a better signal Ona 5/8 wavelength antenna?
Towards the Horizon.
Why is there a coil at the base of a 5/8 Wave Antenna?
It is for Coax Matching.
What is 5/8 Wave Antenna often used for?
VHF & UHF Mobile.
What is a End-Fed Antenna?
A Basic Long-Wire Antenna
Are end-fed antennas likely to be of the correct length?
No. They will need to be matched.
Are End Fed Antennas more or less likely to cause interference (EMC) than other types?
More Likely
What type of Antenna is directional?
Yagi
How many directions are signals from a Yagi directed in?
Mainly One
What are the components of a Yagi Antenna?
A Dipole, with reflectors and several directors.
Yagi Antennas have a …….. gain than other antennas.
Higher
What is gain measured in?
Decibels (dB) (Relative to a high wave dipole).
Define ERP
Effective Radiated Power
What is the ERP Calculation?
ERP (Watts) = transmitted power x gain
What is the ERP?
The directional power of an antenna.
How can a antenna be polarised?
Either Horizontally or Vertically
Can Yagis be Horizontally or Vertically Polarised?
BOTH. Yagis can be polarised either way.
What way are VHF & UHF antennas generally polarised?
Vertically.
Should the antennas be polarised the same way for VHF & UHF?
Yes. The antennas must be polarised the same way for VHF/UHF.
Why does HF polarisation matter less?
It matters less as polarisation for HF as it may be changed by the Ionosphere.
