Receiver Principles Flashcards
What is the purpose of a reciever?
A receiver converts EM energy into usable energy outputting a reproduction of the original signal.
Signals then applied to a loud speaker etc.
What are the three main requirements of an efficient receiver?
- Select a specific signal from other signals at its input and reject the rest.
- Extract intelligence in the modulated signal.
- Produce sufficient power to operate the transducer so we can understand the signals at the output.
What are the 4 characteristics of a receiver?
Sensitivity- to produce a usable output from the weaker signals.
Selectivity- the ability to discriminate between wanted and unwanted signals
Stability- maintain the specific frequency for the receiver
Noise- the ability to produce a distortion free signal ( internal noise).
Define radio frequency (RF)?
The raw state of the Carrier with no intelligence attached
Define audio frequency?
A frequency audible to a human in the range of 20Hz- 20KHz.
Define intermediate frequency?
This frequency is generated by the receiver to help reduce the frequency to make it audible.
Pushed through local oscillators giving an end product which is suitable and between the audible range.
What is heterodyning?
The process of mixing and multiplying two waveforms together.
What is a filter?
Filters allow certain frequencies which are wanted to get through and unwanted to be rejected.
Stop band
Pass band
Name 5 types of filters?
Low pass High pass Band pass Band reject Notch
What is receiver bandwidth?
What the receiver will allow through the filter. This is calculated by the difference between upper and lower cut off frequencies.
What is gain?
Gain is the ratio of output to input power, measured in decibels.
What is automatic gain control? (AGC)
Automatically adjusts the gain so there’s a reasonably constant output with variations in input signal level.
Where would we use AGC?
Mainly used in (AM) amplitude modulation signals, where voice is used.
Explain how squelch works?
Squelch gets rid of any unwanted noise within the signal getting rid of anything below not worth listening to and giving the message.
When we talk about AGC what is attack time ?
The time taken for the AGC to respond to the variations of the input signal level.
