Paragraph 4 Aerial and feeder

Aerial

The aerial shall consist of a dipole of a length not greater than 3 metres nor less than 2 metres, which shall be supported so that its centre is not less than 2 metres above the base of the support when a measurement of field-strength is made.

Feeder

The aerial shall be connected to the aerial input terminals of the apparatus by a twin balanced and screened feeder of a nominal characteristic impedance of 75 ohms. The feeder shall be led at right angles from the dipole for a distance of at least 1 metre.

Balance/Unbalance ratio

The balance/unbalance ratio at the aerial end of the feeder shall be not less than 20 db when measured as follows:—

A generator of internal impedance R, where R is not greater than 5 ohms, shall be connected to the feeder and measuring apparatus as shown in Figure 2(a) and as shown in Figure 2(b) in turn. The ratio e₁/e₂ of the generator e.m.f.'s which produce reference deflection of the meter in the unbalanced connection, (e₁ figure 2(a)) and the balanced connection (e₂ figure 2(b)) respectively, shall be taken as the balance/unbalance ratio.