Feeders (4A1 & 4A2)

 

Feeder

 

The cable used to connect antennas to receivers / transmitters is known as feeder.

 

Feeder is usually co-axial cable (like you see on the aerial lead on TV sets) – because the signal on the inner is screened by the outer braid which retains the signal in the cable.  Co-axial feeder is unbalanced – the outer screen is kept at zero (no signal). Whilst the inner has the signal on it.  

 

Occasionally “ribbon” or “twin” cable (two parallel wires in the same flat plastic sheath) are used.  Two conductors kept at constant separation by insulation - no screen.  Twin feeder is balanced - conductors have equal and opposite voltages/currents/fields.

 

 

 

 

 Feeder Loss

 

Not all the power you put into a feeder gets to the other end.  Some of the RF energy is converted to heat in feeders so they exhibit loss.  Feeder loss is both on Transmit and Receive.  Loss is measured in dB per unit length, so the longer the feeder the greater the loss.   

Feeder loss increases with frequency So low-loss feeder should be used at VHF and UHF  the bigger number of dBs loss, the greater the loss, and less signal gets to the other end.

 

 

 

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