Transmitters and Receivers

Question 1

What is modulation?

Answer 1

A transmitter creates a ‘transmitter wave’ on the required frequency and mixes in the signal to be transmitted

Question 2

What are the two main types of carrier wave?

Answer 2

AM and FM

Question 3

What do AM and FM stand for?

Answer 3

amplitude modulation, frequency modulation

Question 4

What is AM?

Answer 4

the modulated signal increases and decreases in height in relation to the amplitude (volume) of the audio signal

Question 5

What is FM?

Answer 5

the height of the waves are constant but the frequency changes in relation to the volume of the signal. The louder the signal the higher the frequency.

Question 6

What is a sideband?

Answer 6

when we combine the AF with RF it results in sidebands being created - these are just above and just below the carrier frequency - with information identical to the main frequency. There is an upper sideband and lower sideband

Question 7

Why do you only need to transmit ONE of the sidebands? SSB

Answer 7

because it holds identical information, and because you get better results using all your power to send one of the sidebands.

Question 8

Why is SSB more efficient than AM?

Answer 8

it uses less bandwidth because the signal is half as wide.

Question 9

Lower sideband (LSB) operation normally occurs below ___MHz

Answer 9

Lower sideband (LSB) operation normally occurs below 10MHz

Question 10

Upper sideband (USB) operation normally occurs above __MHz

Answer 10

Upper sideband (USB) operation normally occurs above 10MHz

Question 11

What are the four basic transmitter stages?

Answer 11

1. Audio stage - this gets the weak signals from the microphone and amplifies them
2. Frequency Generator (oscillator)
3. Modulator
4. RF Power Amplifier

Question 12

What is demodulation?

Answer 12

The process of recovering the sound from the radio signal.

Question 13

What are the 3 parts of a receiver?

Answer 13

1. Tuning/RF amp
2. Detector (or demodulator)
3. Audio amplfier

Question 14

What does SDR stand for?

Answer 14

Software defined radio

Question 15

Explain what SDR is…

Answer 15

SDR receives radio signals and coverts them into digital for processing in software, not hardware

Question 16

Explain A to D and D to A

Answer 16

analogue to digital, digital to analogue

Question 17

Explain the process of an SDR receiver converting signal to sound

Answer 17

the signal is picked up, converted to digital, processed by the software, converted back to analogue then played from a speaker.

Question 18

Explain the process of an SDR transmitter converting sound to signal

Answer 18

a microphone picks up sound, is converted to digital then a power amplifier is used to send the signal from the transmitting antenna.