Download LOOP INPUT CIRCUITS

LOOP INPUT CIRCUITS
BY,
AISWARYA.PL
LOOP INPUT CIRCUITS:
• The loop antenna is an inductive in nature.
• The loop output is not generally used directly
as an input to the receiver.
• A variety of circuits is used at the input of
direction-finding receivers to obtain a voltage
which larger than the loop voltage.
• The basic elements of a few of these circuits
are shown n fig 2.3
• In fig.2.3(a),the inductance of the loop is
tuned out by a capacitor,the two together
making a series tuned circuit.
• The series tuned circuit provides a certain
amount of circuit magnification of the loop
voltage eL.
• Fig 2.3(b) and 2.3(c) show developments of
the same circuit to achieve a better balance
than is possible with the first circuit.
• One of the Important sources of antenna
effect is the asymmetry of the loop antenna
with respect to the ground.
• To minimize antenna effect,the centre of the
loop is earthed and its output is
thereby,balanced.
• Any residual antenna effect can be
compensated by introducing a controllable
voltage in phase with antenna voltage.
• Balancing of the loop is made more effective
and accurate by enclosing it in a elecrostatic
field.
• Fig 2.3(d),A completely shielded loop will not
pick up any signal but if any break is
introduced,the peformance of the loop is
rarely affected.