Deck 7: Signalling 3 Flashcards
Note:
Most signals are made up of several sine curves, all with different frequencies, added together.
When you play a musical note, what do you hear?
The sound you hear contains the frequency(pitch) of the main note and a load of other frequencies.
What make different instruments sound different, even when they are playing the same note?
-When a musical note is played there is a main frequency and load of other frequencies, its these other frequencies that make instruments sound different, even though they are playing the same note.
What is a spectrum?
The frequencies that make up a signal.
What is bandwidth?
- The range that signal’s spectrum covers is called its bandwidth.
How can you find a signals band width?
You can find a signal’s bandwidth by subtracting the lowest frequency within it from the highest frequency - or by looking at the graph of its spectrum.
What are you doing when you tune a radio?
You scan through the frequencies it’s receiving until you find the one you want. What you are searching for is the frequency of the carrier wave that transmits the signal from your station.
Explain how radio stations transmit their signals?
The audio signal from the music is converted into an electronic signal. This signal is then mixed with a carrier wave, and the combined signal is transmitted.
What does the radio do with the signal it receives from the radio station?
It receives the signal from the radio station, it is able to separate the actual signal from the carrier wave and then convert this back into sound for you to listen to.
Why are different radio stations given a particular carrier frequency?
The carrier frequencies of all the stations in a local area have to be different so that they don’t interfere with each other.
What is the size of gap between frequencies determined by?
- It is determined by the bandwidth of the audio signal- the larger the bandwidth, the larger the gap must be to stop signals at neighbouring carrier frequencies overlapping.
In practice what is the difference between carrier frequencies of radio stations?
0.2MHz
What is the problem with having gaps between carrier frequencies?
That it limits the number of signals that can be transmitted. For example, FM radio can be transmitted between 30MHz and 300MHz. So with a gap of 0.2MHz, there’s only space for (300-30)/0.2= 1350 stations.
What are the two factors that determine the rate of transmission?
1) The number of samples per second
2) The number of bits per sample- High enough so that the transmitted signal closely matches the original, but not so high it is negatively effected by noise.
Rate of transmission of a digital signal(bits per second)=
samples per second x bits per sample
