T7A

Radios, mixers and modulation

Explain what a transceiver, mixer, oscillator, VFO and transverter do, and the difference between sensitivity and selectivity.

11 pool questions1 on the exam

Syllabus: Station equipment: receivers, transceivers, transmitter amplifiers, RF preamplifiers, transverters; Basic radio circuit concepts and terminology: sensitivity, selectivity, mixers, oscillators, Push-To-Talk (PTT), VFO, modulation

A transceiver is a receiver and transmitter in one box

One box, two paths. The PTT input decides which one is live.

Transceiver = transmitter + receiver. PTT (push-to-talk) switches between them: grounding the PTT input means transmit.

Want more power? Add an RF power amplifier to the transceiver's output. Its mode switch (SSB or CW-FM) sets the amplifier for proper operation in that mode. It doesn't change your signal.

RememberPTT grounded = transmit. More power = RF power amplifier.

Oscillators make frequencies, mixers move them

An oscillator generates a signal at one specific frequency. A mixer combines two frequencies to shift a signal to another one.

A mixer shifts a signal to a new frequency. An oscillator supplies the shifting frequency.

The VFO (variable frequency oscillator) is the tuning knob: it sets the receive and transmit frequency.

A transverter puts a mixer around your radio so it works on another band.

Same radio, new band: the transverter converts both what goes out and what comes in.

Part	Job
Oscillator	generates a frequency
Mixer	converts a signal from one frequency to another
VFO	sets the receive and transmit frequency
Transverter	converts a radio's input and output to another band

Modulation puts your voice on a carrier

Voice is too low in frequency to travel as a radio wave. Modulation combines speech with an RF carrier: AM varies its height, FM varies its frequency.

RememberSpeech + carrier = modulation.

Sensitivity hears the faint. Selectivity separates the close.

Sensitivity: how weak can it hear? Selectivity: how close can it tell apart?

Term	Question it answers
Sensitivity	Can it detect a weak signal?
Selectivity	Can it discriminate between signals on nearby frequencies?

Memory hookSensitivity = senses a faint signal. Selectivity = selects one signal from the crowd.

Loading lesson…

Go deeper

Compendium articles on the ideas in this lesson, beyond what the exam asks.

Check what stuck

Practise the 11 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".

Practise T7A →