Module 5 (1.a) - 1D7XX Radio Transmissions

Question 1

Why is the receive oscillator frequency always offset from the received RF signal in a transceiver (and receiver)?

Accepted Answer

In order to recover the Intermediate Frequency (IF).

Question 2

What is the primary function of a radio transmitter?

Accepted Answer

To generate an RF signal to transmit intelligence via an antenna.

Question 3

When the Push-to-Talk (PTT) button is pressed on a half-duplex transceiver, what does the T/R relay do?

Accepted Answer

Switches antenna to transmit side, mutes receive, switches oscillator freq.

Question 4

What is the role of the frequency divider in a PLL?

Accepted Answer

To route a sample of the VCO output to the phase comparator.

Question 5

What is RF control, also known as Transmit Gain Control (TGC), primarily used for?

Accepted Answer

To maintain transmit output power (wattage) within pre-set values.

Question 6

In a typical duty cycle like 20%/80%, what does the lower percentage (20%) represent?

Accepted Answer

The percentage of time for transmitting.

Question 7

For AM signals, what simple component can the detector circuit be?

Accepted Answer

A diode

Question 8

Which component in a transmitter generates the carrier wave?

Accepted Answer

Electronic Oscillator (VCO)

Question 9

What is the function of the detector (demodulator) in a receiver?

Accepted Answer

To extract the intelligence from the IF (carrier).

Question 10

What is a transceiver?

Accepted Answer

A device that contains both a transmitter and a receiver in one package.

Question 11

What is the purpose of filters located throughout the transmitter?

Accepted Answer

To clean up the signal and minimize errors and interference.

Question 12

What circuit is used to keep the oscillator frequency stable and accurate by means of an error voltage?

Accepted Answer

Phase Locked Loop (PLL)

Question 13

What is the role of the mixer in a receiver?

Accepted Answer

To combine oscillator frequency and received RF to recover the IF.

Question 14

What is the role of the modulator/mixer in a transmitter?

Accepted Answer

To superimpose intelligence onto the carrier wave.

Question 15

What is the primary purpose of a radio receiver?

Accepted Answer

To recover the intelligence sent from the distant end.

Question 16

Why is transmit time generally shorter than receive time in field radios with a duty cycle?

Accepted Answer

Transmitting depletes battery quickly and may cause overheating.

Question 17

What is the purpose of an audio amplifier in a transmitter?

Accepted Answer

To increase the strength of audio from the microphone for the modulator.

Question 18

What do control circuits in a transmitter primarily maintain?

Accepted Answer

Output power (Watts) at the selected value.

Question 19

In the heterodyning process in a receiver's mixer, what are the four frequencies typically produced at its output?

Accepted Answer

Receive RF, Oscillator, Sum (USB), and Difference (LSB) frequencies.

Question 20

In AM transmission, what three signals are typically present at the output of the modulator?

Accepted Answer

Carrier, Upper Sideband (USB), Lower Sideband (LSB).

Question 21

Which of these is an example of a programmable processing technology used in SDR?

Accepted Answer

Field Programmable Gate Array (FPGA)

Question 22

Which component in a receiver selects the desired receive frequency and rejects others?

Accepted Answer

Tuner

Question 23

What is the purpose of Automatic Gain Control (AGC) in a receiver?

Accepted Answer

To control the output level (volume) of the intelligence.

Question 24

Which category of transceiver uses 2 frequencies (1 for transmit, 1 for receive)& switches between functions when keyed?

Accepted Answer

Half-Duplex

Question 25

Which element of a PLL compares two signals and detects their phase difference?

Accepted Answer

Phase comparator/detector

Question 26

What is the Intermediate Frequency (IF) in a receiver?

Accepted Answer

The frequency to which the radio signal is converted during heterodyning.

Question 27

What is the purpose of an RF amplifier in a transmitter?

Accepted Answer

To increase signal power to increase transmit distance.

Question 28

What is modulation?

Accepted Answer

The process of superimposing an input signal onto a carrier wave.

Question 29

What additional component is typically found in a transceiver to switch between transmit and receive functions?

Accepted Answer

A Transmit/Receive Relay (T/R Relay).

Question 30

What is the role of the oscillator in a receiver?

Accepted Answer

To provide the frequency used in the mixer to recover the IF.

Question 31

What is the function of the RF amplifier in a receiver?

Accepted Answer

To increase the level of the weak received signal.

Question 32

What does "keying the radio" typically do?

Accepted Answer

Applies power to transmit circuits and releases oscillator to modulator.

Question 33

Which category of transceiver can transmit and receive at the same time?

Accepted Answer

Full-Duplex

Question 34

What does "duty cycle" refer to in transceivers operating in simplex or half-duplex mode?

Accepted Answer

The percentage of time to transmit and percentage of time to receive.

Question 35

In AM half-duplex transceiver signal flow, which components are typically shared/cross-utilized for transmit & receive?

Accepted Answer

Power supplies and oscillators.

Question 36

What is Software Defined Radio (SDR)?

Accepted Answer

Radio where physical layer functions are software defined.

Question 37

How does AGC help in a receiver?

Accepted Answer

It corrects for fading of the receive signal and equalizes levels.

Question 38

Which category of transceiver uses one frequency for both transmit and receive, preventing simultaneous operation?

Accepted Answer

Simplex

Question 39

Where is an antenna coupler typically placed?

Accepted Answer

At the antenna feed point.

Question 40

What is a primary advantage of SDR technology over traditional hardware-based radios?

Accepted Answer

SDRs allow enhancements via software/firmware without new hardware.

Question 41

Where is an antenna tuner typically placed?

Accepted Answer

At the output of the transmitter.

Question 42

In the AM receive signal flow, what component typically follows the RF Amplifier?

Accepted Answer

Mixer

Question 43

In a receiver's tuner, what components typically form the circuit that resonates at the desired frequency?

Accepted Answer

An inductor and a capacitor.

Question 44

What is the function of an antenna tuner/coupler?

Accepted Answer

To match impedance for maximum power transfer to the antenna.

Question 45

How does a Voltage-Controlled Oscillator (VCO) create a carrier wave?

Accepted Answer

By converting DC current into a continuous AC waveform.

Module 5 (1.a) - 1D7XX Radio Transmissions

Questions 45

Module 5 (1.a) - 1D7XX Radio Transmissions

Questions 45