4. Feeders & Antennas

Question 1

what are feeders used for?

Answer 1

Connecting the transmitter/receiver to the antenna?

Question 2

What happens to feeders on transmit and receive?

Answer 2

Feeders exhibit ‘loss’ on transmit & receive.

Question 3

T/F The longer the cable, the less amount of loss experienced?

Answer 3

FALSE: More loss is experienced the greater the length of the cable.

Question 4

Why does loss occur?

Answer 4

Loss occurs as some of the RF energy is converted to heat.

Question 5

What else affects feeder loss?

Answer 5

Frequency.

Question 6

What kind of feeder is recommended for VHF & UHF ?

Answer 6

Thicker, low-loss feeder cable is recommended.

Question 7

What are the two types of feeder?

Answer 7

Coaxial & Twin Feeder (Ladder-lined)

Question 8

Which kind of feeder is more commonly used by amateurs, Coaxial or Ladder Line?

Answer 8

Coaxial.

Question 9

T/F: Twin Feeder Cable is balanced.

Answer 9

TRUE. Twin Feeder is balanced, Coaxial Cable is unbalanced.

Question 10

T/F: Twin Feeder has two wires for equal and opposite signals

Answer 10

True. This is why its balanced.

Question 11

What keeps the signal within coaxial cable?

Answer 11

The Outer braid (screen)

Question 12

How many types of connector are there?

Answer 12

Four.

Question 13

What connector is commonly used for HF?

Answer 13

PL259

Question 14

What is the N Connector commonly used for?

Answer 14

VHF & UHF

Question 15

What is the one type of connector which is not screw thread locking?

Answer 15

BNC - It is bayonet locking.

Question 16

What connector is common for handheld radios?

Answer 16

SMA

Question 17

What Ohm BNC connector is used and why?

50 or 70

Answer 17

50 Ohm - the 75 Ohm is not used as it has a different type of pin.

Question 18

What do antennas do?

Answer 18

Convert Electrical Signals into Radio Waves (and vice-versa)

Question 19

T/F: Antennas are designed for specific frequencies.

Answer 19

TRUE. They are also different sizes depending on the band.

Question 20

In general, Lower Frequencies (Longer Wavelengths) require…..?

Answer 20

Larger Antennas.

Question 21

Name 3 of the 5 antenna types.

Answer 21

• Yagi
• Dipole
• 5/8 Wave
• 1/4 Wave
• Long Wire

Question 22

Is a Dipole a balanced or unbalanced antenna?

Answer 22

Balanced.

Question 23

How long (in Wave Lengths) is a Dipole Antenna?

Answer 23

Half a Wavelength.

Question 24

How long would a dipole antenna need to be to work in 14Mhz?

Answer 24

14Mhz is the 20 metre band, so 10 metres, as it is half a wavelength long.

Question 25

What does a Polar Pattern show?

Answer 25

A polar pattern shows how RF signals radiate from the antenna.

Question 26

Where are Omni-Directional signals directed?

Answer 26

Omni-Directional signals are directed in all directions.

Question 27

What type of Antenna is Omni - Directional?

Answer 27

Dipole

Question 28

How long must a 1/4 wave Ground Plane Antenna be to work at 144Mhz (2m Band)

Answer 28

50cm Long

Question 29

What forms the ground plane on a antenna?

Answer 29

4 Horizontal Wires

Question 30

What are the 4 horizontal wires are used as the ground planes called?

Answer 30

Radials

Question 31

What do the radials do?

Answer 31

They form a ground plane which act as a mirror for radio signals.

Question 32

How long is a 5/8 Wave Ground Plane Antenna?

Answer 32

A 5/8 of a wavelength

Question 33

Where do you get a better signal Ona 5/8 wavelength antenna?

Answer 33

Towards the Horizon.

Question 34

Why is there a coil at the base of a 5/8 Wave Antenna?

Answer 34

It is for Coax Matching.

Question 35

What is 5/8 Wave Antenna often used for?

Answer 35

VHF & UHF Mobile.

Question 36

What is a End-Fed Antenna?

Answer 36

A Basic Long-Wire Antenna

Question 37

Are end-fed antennas likely to be of the correct length?

Answer 37

No. They will need to be matched.

Question 38

Are End Fed Antennas more or less likely to cause interference (EMC) than other types?

Answer 38

More Likely

Question 39

What type of Antenna is directional?

Answer 39

Yagi

Question 40

How many directions are signals from a Yagi directed in?

Answer 40

Mainly One

Question 41

What are the components of a Yagi Antenna?

Answer 41

A Dipole, with reflectors and several directors.

Question 42

Yagi Antennas have a ........ gain than other antennas.

Answer 42

Higher

Question 43

What is gain measured in?

Answer 43

Decibels (dB) (Relative to a high wave dipole).

Question 44

Define ERP

Answer 44

Effective Radiated Power

Question 45

What is the ERP Calculation?

Answer 45

ERP (Watts) = transmitted power x gain

Question 46

What is the ERP?

Answer 46

The directional power of an antenna.

Question 47

How can a antenna be polarised?

Answer 47

Either Horizontally or Vertically

Question 48

Can Yagis be Horizontally or Vertically Polarised?

Answer 48

BOTH. Yagis can be polarised either way.

Question 49

What way are VHF & UHF antennas generally polarised?

Answer 49

Vertically.

Question 50

Should the antennas be polarised the same way for VHF & UHF?

Answer 50

Yes. The antennas must be polarised the same way for VHF/UHF.

Question 51

Why does HF polarisation matter less?

Answer 51

It matters less as polarisation for HF as it may be changed by the Ionosphere.