Information and communication: transmission with waves

By Fintan Darragh

This a large part of AS physics and one of the easier parts of the course to remember and get good marks on. Often they’ll throw a long-answer question at you based on ‘Information and Communication’, and by remembering the points below you’ll be able to answer them expertly.

What are the stages of a real time communication system?

With AQA it is very likely you’ll be asked to fill several spaces in a block diagram (as shown below).

Or, as a simple list:

1. information input
2. input transducer (e.g. microphone)
3. modulator
4. amplifier
5. transmitter (e.g. aerial)
6. the transmission path (e.g. radio waves)
7. receiver (e.g. aerial)
8. amplifier
9. demodulator
10. output transducer (e.g. speaker)

Since remembering what things exist within the actual system is easier than remembering where they go (and you’ll need to know both), take special notice of where the amplifiers are and how they are positioned symmetrically within the system.

What does the modulator do?

The modulator uses the information it is given to modify the carrier wave. For instance, if the signal is to be an AM wave, it will modify the amplitude of the carrier wave, or if the wave is to be an FM wave it will modify the frequency of the carrier wave.

Important exam questions

These are specific questions which you need to understand and know the answer in and out. It is likely they’ll come up at some point in the exam, and they’re potentially long-answer (high-mark) questions.

What is time division multiplexing and why do we use it?

• Many samples are transmitted down the same channel
• in binary code
• over a short period of time

• a sampling process is required
• the signals are then transmitted in sequence

• secure
• cheaper
• more efficient than a multi-transmitter system (bandwidth)

What methods and frequencies are good for long distance communication?

Usually this question will exclude easier methods such as fibre optic cables or simply by freight.

• transmitted to a satellite and retransmitted down to earth
  using microwaves
• transmitted to and from intermediate transmitters
  using VHF/UHF waves
• diffracted around the Earth’s surface
  using long/medium waves
• reflected/refracted off of the Earth’s ionosphere
  using high frequency waves

Other little bits of information

• At higher frequencies (or lower wavelengths), only line-of-sight transmission is possible.
• Transmission is slower in cables than in free space.

Nail this topic

Buster Tests already has a great set of AS physics questions and answers for you to try out, which are especially good when it comes to the calculation side of things (such as bandwidth).