Technician License Course Chapter 3 Types of Radios and Radio Circuits Module 7

The Basic Radio Station

Basic Station Organization Station Equipment –Receiver –Transmitter –T R Switch –Antenna –Power Supply Accessory Station Equipment Microphones, CW Keys, etc.

Well equipped station

Transmit/Receive (TR) Switch If the station antenna is shared between the transmitter and receiver, the TR switch allows the antenna to be switched to the transmitter when sending and to the receiver when receiving. –In a transceiver, this TR switch is inside the unit and requires no attention by the operator.

What Happens During Radio Communication? Transmitting (sending a signal): –Information (voice, data, video, commands, etc.) is converted to electronic form. –The information in electronic form is attached or embedded on a radio wave (a carrier). –The radio wave is sent out from the station antenna into space.

What Happens During Radio Communication? Receiving end: –The radio wave (carrier) with the information is intercepted by the receiving station antenna. –The receiver extracts the information from the carrier wave. –The information is then presented to the user in a format that can be understood (sound, picture, words on a computer screen, response to a command).

What Happens During Radio Communication? This sounds pretty simple, but it in reality is pretty complex. This complexity is one thing that makes ham radio fun…learning all about how radios work. Don’t be intimidated. You will be required to only know the basics, but you can learn as much about the “art and science” of radio as you want.

Simple CW Transmitter Block Diagram

Receiver Circuits Oscillators produce signals at a desired frequency. Mixers combine signals, and produce both the sum and difference of the input signals. Filters remove unwanted frequencies or signals. Pre –amplifiers and amplifiers increase signal levels.

Receiver Design It is always a challenge for receiver designers to balance the competing traits of selectivity and sensitivity. Selectivity expresses how well a receiver rejects adjacent signals. Sensitivity expresses how faint a signal can be detected. Product detectors are used in receivers for SSB and CW signals to extract the modulation. Frequency discriminators are used in receivers for FM signals to extract the modulation.

Transmitter Circuits A modulator combines audio and RF signals. A power amplifier increases the level of the modulated signal. Power amplifiers can be added externally to increase the transmitted signal strength. A transverter is a device that converts a carrier frequency to another frequency. ( Eg: 28 Mhz to 220Mhz )

Receiver Block Diagram

Receiver Block Diagram w/ Preamp Pre-amplifier A pre-amplifier can be inserted between the antenna and receiver input to increase receiver sensitivity to weak signals.

Superheterodyne Receiver One of the most widely used AM, SSB, and CW receiver designs is the superheterodyne receiver. The incoming signal is mixed with a local oscillator to produce an intermediate frequency, which is sent to a product detector for mixing with a beat frequency oscillator. The resulting audio frequency is amplified, and comes out the speaker. Single conversion superhet receivers use a single IF stage. Dual conversion superhet receivers use two IF stages.

The Superheterodyne Receiver Block Diagram

FM Receivers FM receivers are designed to detect the frequency variations on the carrier that are produced by this type of modulation. A frequency discriminator detects the variation from the carrier frequency. FM signals are less affected by natural noise than AM signals.

The FM Receiver Block Diagram

What is the function of a product detector? (T7A01) A. Detect phase modulated signals B. Demodulate FM signals C. Detect CW and SSB signals D. Combine speech and RF signals

What is the function of a product detector? (T7A01) A. Detect phase modulated signals B. Demodulate FM signals C. Detect CW and SSB signals D. Combine speech and RF signals

What type of receiver is shown in Figure T6? (T7A02) A. Direct conversion B. Super-regenerative C. Single-conversion superheterodyne D. Dual-conversion superheterodyne

What type of receiver is shown in Figure T6? (T7A02) A. Direct conversion B. Super-regenerative C. Single-conversion superheterodyne D. Dual-conversion superheterodyne

What is the function of a mixer in a superheterodyne receiver? (T7A03) A. To reject signals outside of the desired passband B. To combine signals from several stations together C. To shift the incoming signal to an intermediate frequency D. To connect the receiver with an auxiliary device, such as a TNC

What is the function of a mixer in a superheterodyne receiver? (T7A03) A. To reject signals outside of the desired passband B. To combine signals from several stations together C. To shift the incoming signal to an intermediate frequency D. To connect the receiver with an auxiliary device, such as a TNC

What circuit is pictured in Figure T7, if block 1 is a frequency discriminator? (T7A04) A. A double-conversion receiver B. A regenerative receiver C. A superheterodyne receiver D. An FM receiver

What circuit is pictured in Figure T7, if block 1 is a frequency discriminator? (T7A04) A. A double-conversion receiver B. A regenerative receiver C. A superheterodyne receiver D. An FM receiver

What is the function of block 1 if figure T4 is a simple CW transmitter? (T7A05) A. Reactance modulator B. Product detector C. Low-pass filter D. Oscillator

What is the function of block 1 if figure T4 is a simple CW transmitter? (T7A05) A. Reactance modulator B. Product detector C. Low-pass filter D. Oscillator

What device takes the output of a low- powered 28 MHz SSB exciter and produces a 222 MHz output signal? (T7A06) A. High-pass filter B. Low-pass filter C. Transverter D. Phase converter

What device takes the output of a low- powered 28 MHz SSB exciter and produces a 222 MHz output signal? (T7A06) A. High-pass filter B. Low-pass filter C. Transverter D. Phase converter

If figure T5 represents a transceiver in which block 1 is the transmitter portion and block 3 is the receiver portion, what is the function of block 2? (T7A07) A. A balanced modulator B. A transmit-receive switch C. A power amplifier D. A high-pass filter

If figure T5 represents a transceiver in which block 1 is the transmitter portion and block 3 is the receiver portion, what is the function of block 2? (T7A07) A. A balanced modulator B. A transmit-receive switch C. A power amplifier D. A high-pass filter

Which of the following circuits combines a speech signal and an RF carrier? (T7A08) A. Beat frequency oscillator B. Discriminator C. Modulator D. Noise blanker

Which of the following circuits combines a speech signal and an RF carrier? (T7A08) A. Beat frequency oscillator B. Discriminator C. Modulator D. Noise blanker

Which of the following devices is most useful for VHF weak-signal communication? (T7A09) A. A quarter-wave vertical antenna B. A multi-mode VHF transceiver C. An omni-directional antenna D. A mobile VHF FM transceiver

Which of the following devices is most useful for VHF weak-signal communication? (T7A09) A. A quarter-wave vertical antenna B. A multi-mode VHF transceiver C. An omni-directional antenna D. A mobile VHF FM transceiver

What device increases the low-power output from a handheld transceiver? (T7A10) A. A voltage divider B. An RF power amplifier C. An impedance network D. A voltage regulator

What device increases the low-power output from a handheld transceiver? (T7A10) A. A voltage divider B. An RF power amplifier C. An impedance network D. A voltage regulator

Which of the following circuits demodulates FM signals? (T7A11) A. Limiter B. Discriminator C. Product detector D. Phase inverter

Which of the following circuits demodulates FM signals? (T7A11) A. Limiter B. Discriminator C. Product detector D. Phase inverter

Which term describes the ability of a receiver to discriminate between multiple signals? (T7A12) A. Tuning rate B. Sensitivity C. Selectivity D. Noise floor

Which term describes the ability of a receiver to discriminate between multiple signals? (T7A12) A. Tuning rate B. Sensitivity C. Selectivity D. Noise floor

Where is an RF preamplifier installed? (T7A13) A. Between the antenna and receiver B. At the output of the transmitter’s power amplifier C. Between a transmitter and antenna tuner D. At the receiver’s audio output

Where is an RF preamplifier installed? (T7A13) A. Between the antenna and receiver B. At the output of the transmitter’s power amplifier C. Between a transmitter and antenna tuner D. At the receiver’s audio output