Foundation Radio Amateur Licence - BDARS Online Syllabus

5. Feeder and Antenna

Feeder requirements
Recall the correct cable to use for r.f. signals and that coaxial cable is most widely used because of its screening properties.

Recall that the plugs and sockets for r.f. should be of the correct type and that the braid of coaxial cable must be correctly connected to minimise r.f. signals getting into or out of the cable.Identify BNC and PL259 plugs.

Types of antenna
Recall that the purpose of an antenna is to convert electrical signals into radio waves (and vice-versa) and that these are polarised according to the orientation of the antenna, e.g. a horizontally oriented antenna will radiate horizontally polarised waves.

Identify the half-wave dipole, l/4 ground plane, Yagi, end-fed wire and 5/8l antennas.
Understand that the sizes of h.f. and v.h.f. antennas are different because they are related to wavelength, though they operate on the same basic principles.Understand that the l/2 dipole has a physical length approximately equal to a half wavelength of the correct signal.

Antenna basics
Understand that half-wave dipoles (mounted vertically), ground planes and 5/8l antennas are omni-directional.

Understand that a Yagi antenna is directional and has a gain because of its focussing ability.

Recall that e.r.p. is the product of the power to the antenna and its gain.

Recall that the antenna system must be suitable for the frequency of the transmitted signal. Recall that if an antenna is not correctly
designed for the frequency it will not match the transmitter and will not work effectively.

Recall that at h.f., where an antenna has not been designed for the particular frequency, an ATU (antenna tuning unit) makes it possible for the antenna to accept power from the transmitter.

Balanced antennas
Recall the difference between balanced and unbalanced antennas and that a balun should be used when feeding an h.f. dipole with coaxial cable (which is unbalanced).

Understand Standing Wave Ratios (SWR)

Recall that an SWR meter shows whether an antenna presents the correct match to the transmitter and is reflecting minimum power back to the transmitter.

Recall that a high SWR (measured at the transmitter) is an indication of a fault in the antenna or feeder (and not the transmitter). (Relate this to item 4b.5.)

Dummy loads
Recall that a “dummy load” is a screened resistor connected instead of an antenna to allow the transmitter to be operated without radiating a signal.