This group covers the building blocks inside amateur stations: receivers, transmitters, transceivers, amplifiers and the basic circuits that make them work. You need the vocabulary and what each part does, not the circuit math.
Receiver performance terms
Two terms are easy to confuse.
Sensitivity is the ability of a receiver to detect the presence of a weak signal. A more sensitive receiver can hear fainter stations.
Selectivity is the ability to discriminate between signals, picking out the one you want while rejecting strong ones nearby in frequency.
RF gain is just a control that adjusts amplification. Total harmonic distortion measures how much unwanted harmonic content a circuit adds to a signal. Neither one describes these abilities.
Radio building blocks
Oscillator: a circuit that generates a signal at a specific frequency.
VFO (variable frequency oscillator): the tunable oscillator that sets both the receive and transmit frequency in a transceiver. (Making CW audible as a tone is the job of a different circuit, the beat frequency oscillator.)
Mixer: combines two signals to produce sum and difference frequencies, converting a signal from one frequency to another.
Modulation: combining information, such as speech, with an RF carrier signal.
Phase splitter, inverter and amplifier do other jobs and do not convert frequency.
Transmitting equipment
A transceiver is a single device combining a receiver and a transmitter. An antenna tuner (not a transceiver) matches feed line impedance.
A transverter converts the RF input and output of a transceiver to another band. For example, it lets a transceiver for one band operate on a very different band, such as VHF, UHF or microwave.
An RF power amplifier added to a transceiver’s output increases transmitted power. A potentiometer is simply a variable resistor and cannot do this.
Some VHF power amplifiers have a mode switch selecting SSB or CW-FM. It does not change the transmitted mode. It sets the amplifier for proper operation in the selected mode, because SSB needs linear amplification while CW and FM do not.
Push-to-talk
The PTT (push-to-talk) input switches the transceiver from receive to transmit when it is grounded. A microphone button, a foot switch or a data interface can ground this line. It is not the key input for CW and does not create tuning tones.
Key facts to memorize
Sensitivity = detecting weak signals; selectivity = discriminating between signals.
Mixer = converts a signal from one frequency to another.
Oscillator = generates a signal at a specific frequency.
VFO = sets the receive and transmit frequency.
Transceiver = receiver plus transmitter in one unit.
Transverter = converts transceiver RF input and output to another band.
PTT grounded = transmit.
Modulation = combining speech (or other information) with an RF carrier.
RF power amplifier = increases transmitter output power.
A mixer blends two frequencies into new ones, like a blender.
A trans-verter is a band translator.
Questions in this group (11): answers shown
T7A01
Which term describes the ability of a receiver to detect the presence of a signal?
A. RF gain
B. Sensitivity ✓ Correct answer
C. Selectivity
D. Total Harmonic Distortion
Sensitivity is how weak a signal a receiver can detect and turn into usable output. Selectivity is a different property, covering the ability to separate nearby signals, and RF gain only controls amplification.
T7A02
What is a transceiver?
A. A device that combines a receiver and transmitter ✓ Correct answer
B. A device for matching feed line impedance to 50 ohms
C. A device for automatically sending and decoding Morse code
D. A device for converting receiver and transmitter frequencies to another band
A transceiver combines a receiver and a transmitter in one housing, usually sharing circuits such as the frequency control and the antenna connection. An antenna tuner, not a transceiver, matches feed line impedance.
T7A03
Which of the following is used to convert a signal from one frequency to another?
A. Phase splitter
B. Mixer ✓ Correct answer
C. Inverter
D. Amplifier
A mixer combines two signals and produces sum and difference frequencies, which lets a circuit shift a signal from one frequency to another. This is how superheterodyne receivers create their intermediate frequency.
T7A04
Which term describes the ability of a receiver to discriminate between multiple signals?
A. Discrimination ratio
B. Sensitivity
C. Selectivity ✓ Correct answer
D. Harmonic distortion
Selectivity is the ability of a receiver to pick out the desired signal while rejecting others close to it in frequency. Sensitivity, by contrast, is about detecting weak signals at all.
T7A05
What is the name of a circuit that generates a signal at a specific frequency?
A. Reactance modulator
B. Phase modulator
C. Low-pass filter
D. Oscillator ✓ Correct answer
An oscillator is a circuit that generates a signal at a particular frequency, often controlled by a tuned circuit or crystal. Modulators impress information on a signal, and a low-pass filter only passes lower frequencies.
T7A06
What device converts the RF input and output of a transceiver to another band?
A. High-pass filter
B. Low-pass filter
C. Transverter ✓ Correct answer
D. Phase converter
A transverter shifts both the RF input and output of a transceiver to another band, such as using a 10-meter radio to operate on 2 meters or microwaves. Filters only pass or block frequency ranges and do not convert them.
T7A07
What is the function of a transceiver’s PTT input?
A. Input for a key used to send CW
B. Switches transceiver from receive to transmit when grounded ✓ Correct answer
C. Provides a transmit tuning tone when grounded
D. Input for a preamplifier tuning tone
Push-to-talk (PTT) is a control input that switches the transceiver from receive to transmit when it is grounded, as when you press the microphone button. It is not a CW key input or a tuning tone.
T7A08
Which of the following describes combining speech with an RF carrier signal?
A. Impedance matching
B. Oscillation
C. Modulation ✓ Correct answer
D. Low-pass filtering
Modulation is the process of combining information, such as speech, with an RF carrier so the carrier can convey it. Oscillation merely generates the carrier, and impedance matching and filtering do not add information.
T7A09
What is the function of the switch which selects either SSB or CW-FM on some VHF power amplifiers?
A. Change the mode of the transmitted signal
B. Set the amplifier for proper operation in the selected mode ✓ Correct answer
C. Change the frequency range of the amplifier to operate in the proper segment of the band
D. Reduce the received signal noise
The mode switch on a VHF power amplifier configures the amplifier for correct operation in the selected mode. SSB needs linear amplification, while CW and FM can use a more efficient setup. The switch does not change the transmitted mode or frequency range.
T7A10
What can be added to the output of a transceiver to increase the transmitted output power?
A. A potentiometer
B. An RF power amplifier ✓ Correct answer
C. An impedance multiplier
D. All these choices are correct
An RF power amplifier boosts the transceiver's output to a higher power level. A potentiometer is just a variable resistor, and an impedance multiplier is not a real power-boosting device, so 'all of these' is wrong.
T7A11
What is the function of the Variable Frequency Oscillator (VFO) circuit in a transceiver?
A. Set the receive and transmit frequency ✓ Correct answer
B. Provide automatic frequency control
C. Inject a variable frequency to allow CW reception
D. Generate and demodulate single sideband signals
The VFO is the tunable oscillator that sets the operating frequency, both receive and transmit, in a transceiver. Injecting a signal that beats against a CW carrier to produce an audible tone is the job of the beat frequency oscillator (BFO), not the VFO.