Foundation Licence

Feeders and Antennas

What they do

Feeder: transfers RF current between a transceiver and antenna without radiating radio waves. (Hope springs eternal).

Antenna: transfers RF energy with best possible efficiency from RF current to RF wave or from RF wave to RF current.

Types of Feeder

Coaxial Cable (coax)

Ribbon Feeder

Open Wire Feeder

Types of Plug

BNC Plug

PL 259 Plug

Types of Antenna

At Foundation Level:

Half Wave Dipole ¼ Wave ground plane 5/8 ground plane Yagi antenna End fed wire.

The Half – Wave Dipole

hal

f w

avel

en

gth

Transceiver

dip

ole

¼ Antenna

Coax Feed

5/8 Antenna

• Improved low angle radiation pattern

• Has ‘gain’ (4dB)

• Coil: for matching to transmitter (adds 1/8 )

The Yagi Antenna

Ways of indicating “Gain”

3dB

6dB

9dB

10dB

2 times

4 times

8 times

10 times

Effective Radiated Power (erp)

erp = antenna gain × transmit power

Polarisation

Direction of Polarisation is the same as the direction of electric field.

Vertical Polarisation

Horizontal Polarisation

Matching Antennas / Feeders

Source of Energy Load

Matching Antennas

Source of Energy Load

Energy reflected back to source

SWR: Standing Wave Ratio

How good a match?

You don’t have to know this yet!

But…

Antenna Tuning Unit (ATU)

SWR Meter

Variation of SWR with Dipole Length

Dummy Loads

It’s all a matter of balance

Balance = electrical symmetry

The Balun

Retains the electrical symmetry of a balanced antenna if we connect it to an unbalanced feeder.

Dipole Antenna

(Balanced)

Coaxial cable feeder

(unbalanced)

Balun