# UK Amateur Radio ## Foundation Licence 2002
### Transmitters and Receivers Part B
### Receivers |
Simple block or "concept" diagrams of a receiver.
The block diagram shown opposite is that used for all assessment question. As with the transmitter the block diagrams are not intended to show a particular radio receiver but merely indicate the function they need to perform. You can see the aerial at the left hand end. 1=Tuning and Rf amplifier stage 2=Detection Stage 3= Audio amplification stage 4=Loudspeaker.
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.
Picture of a variable capacitor
Once the signal has been selected and amplified it is passed to the Detection stage where the original modulated signal is "recovered" and then passed to stage 3 where the audio is amplified so that you can hear it or if you are working a digital mode, pass it to the remainder of the equipment so that it can be decoded. It is still good practice to be able to hear a digital signal then at least you know when the equipment should be decoding something!!! Caution: If you use headphones remember that damage to hearing can occur if the audio level is too high.

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