Technical requirements of a radio receiver
Just like the transmitter the aerial is connected to the receiver using a
feeder. Today it is more usual to have the transmitter and the receiver all
together in one box whilst years ago the items were kept separate. Thus the
same feeder and aerial is used to transmit and receive with a change over
relay in the equipment so that the transmitted signal does not go directly
into the receiver - and damage it !!!!!
In fact when the signal is received at stage 1 it is so weak that it needs
to be amplified before it is of any use to the other stages. Hence the need
to have an RF Amplifier in stage 1. Also stage 1 is used to tune the equipment
to the desired frequency. Whilst you do not need to understand this in detail
the signal is tuned by the use of inductors and capacitors which form what
is called a "tuned" circuit and this filters out unwanted signals.
This is refered to as selectivity
In old equipment the frequency was usually changed by the use of a variable
capacitor which is connected to the tuning knob on the equipment but today's
modern equipment can be tuned in a number of ways including a digital
key pad or knob controlling a digital frequency synthesizer.
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