5. Radio Communication Equipment Flashcards
How is a carrier wave generated?
A carrier wave is generated by an oscillator.
How is the carrier wave modulated?
The carrier wave is modulated with signal wave (audio) and the modulated wave is amplified to the required power for transmission.
What is the purpose of a side tone circuit?
The side tone circuit allows pilots to monitor their own transmission. Transmission signal is partially fed back to the receiving system for this purpose.
Antenna tuner
Antenna
With an antenna tuner a HF radio resonates on the frequency of transmission.
The antenna converts RF current into radio waves for transmission into space.
How many side band does amplitude modulation produce?
Amplitude modulation produces two side bands.
Why is single side band (SSB) used?
Single side band uses one side band only because either one side band contains all message information.
(It can operate at lower power by not producing a CW or another side band). Or if the power is the same the signal will be much stronger.
SSB uses less band width than DSB transmission.
Which radio services employ SSB?
Communication using HF and lower frequencies employ SSB, except MF broadcasting.
Which side band does an airborne HF communication system use?
The airborne HF communication system uses the upper side band (USB) only.
How does the use of SSB affect frequency bandwidth?
The frequency band width occupied by SSB is less than that of DSB.
How do strong signals affect a radio’s auto gain control (AGC).
With strong signals the voltage of automatic gain control (AGC) gets high, and the receiver gain is reduced to prevent overloading.
What happens to AGC with weak signals?
With weak signals AGC voltage gets low and receiver gain is increased.
What does the squelch control do?
The squelch control mutes the audio amplifier when the strength of the incoming signal is lower than the given squelch level.
(And so removes the weak annoying signal)
What is the difference between HF and VHF squelch control?
HF receiver’s squelch control is set by the pilots while VHF squelch is preset.
Advantages of SSB
- Efficient use of transmission power
- Narrow frequency band width
- Less effect of fading
Disadvantages of SSB
- Equipment is complex
- High level of frequency stability is required
(Means the equipment is expensive)
