Book 2 Flashcards
Identify 3 effects of over modulation
Distortion
Wasted Power
Adjacent channel interference
Explain the purpose and operation of VOGAD (Voice Operated Gain Adjustment Device)
VOGAD ensures that the modulation level is always correct.
If the operator speaks loudly it reduces gain, if the operator speaks quietly it increases gain.
Identify the power levels at 100% modulation for each signal
Carrier = 2/3rd
USB = 1/6th
LSB = 1/6th
Master Oscillator
This generates the carrier signal at the required transmission frequency.
Buffer Amplifier
Protects the Master oscillator from output discrepancies due to loading.
Modulator Stage
The modulator converts the audio signal into a Radio Frequency. The modulator provides 3 output signals, the RF carrier, the USB
and the LSB.
AF Amplifier (Transmitter)
provides sufficient audio power to give the required modulation depth.
Driver Amplifier
To ensure that the PA receives a large enough signal to enable maximum PA output.
Power Amplifier (PA)
The PA amplifies the RF signal to provide Sufficient RF power to the Aerial to ensure the signal reaches the receiver
Aerial
The aerial converts conventional electrical energy into electromagnetic
energy, allowing the signal to radiate.
Side Tone
The main purpose of a side tone system is to prevent the pilot from shouting
and therefore over modulating the transmitter.
b. A secondary use of side tone is to give the pilot confidence that the transmitter
is actually working.
Explain the terms used in receivers
- Signal to Noise Ratio
-Selectivity
-Fidelity
-Sensitivity
*Signal to Noise Ratio = Level of how much noise there is compared to the signal
- Selectivity = Ensuring you receive the wanted signal and rejecting all other signals
- Fidelity = Produce a high quality output at the headset
- Sensitivity = Take a weak small signal and ensure it produces a usable output
What determines the polarisation of a signal
E Wave
Superheterodyne Principle
Converts all incoming RF frequencies into a lower, fixed, useable frequency
Local Oscillator
Produces a frequency which is different to the incoming signal by a constant amount.
Mixer
Mixes the incoming and local oscillator signals to produce the intermediate frequency
IF AMP
Amplifies IF gain by 10^6 and prevents adjacent channel interference
Advantages of using RF amplifier
Reduces 2nd Chanel interference
Prevents IF breakthrough
Prevents L.O. radiation
Improves receivers SNR
AF Detector
Demodulates IF to AF
AF AMP (Receiver)
Provides powerful signal to drive the headset
Squelch Gate
To prevent operator fatigue by stopping noise from hurting the pilots ears
AGC (receiver)
To maintain constant audio output under changing aerial conditions
Purpose of tone oscillator
Produces a 1khz audible test tone
Purpose of TX/RX relay
switches to TX or receiver
