Accelerated Technician Class Session #3

Circuit Components The stuff radios are made of. Right: Scorpion Antenna goes with the “Go Kit”

Resistors A ohms 12 volts As we have seen, resistors limit the flow of current. 3 Amps

Adding Resistors in Series R t = R 1 + R 2 + R 3 + … + R n

Adding Resistors in Parallel R 1 + R 2 1 R1R1R1R1 + 1 R2R2R2R2 + 1 R3R3R3R3 + …1 R 1 x R 2 R t = If only 2 resistors: R t = If all resistors are equal: R t = R / n + 1 RnRnRnRn

Resistors

Resistors

Resistor Summary Resistors oppose (resist) the flow of current. Resistors add in series, “reciprocal of sum of reciprocals” in parallel. Resistors vary in size and material according to heat dissipation. The unit of measurement is the Ohm (Ω).

DC and AC Direct Current Direct Current Alternating Current

A Word about Magnets Remember: 1. Like charges repel and opposite charges attract opposite charges attract 2. We can induce a current in a conductor passing in a conductor passing through a magnetic through a magnetic field. field.

Inductors

Inductors Anytime current flows through a conductor, a magnetic field is created around that conductor.

Inductors If we form the conductor into a coil shape, we can greatly intensify the strength of the magnetic field. We can store energy in this magnetic field.

Inductors When we close the switch, current flows through the inductor, building a magnetic field. When we open the switch, the field collapses, inducing a current in the inductor.

Inductors The value of an inductor can be varied by: Coil Spacing Coil Diameter Number of Turns Core Material The unit of measurement is the Henry (H).

Adding Inductors In Series circuits: L t = L 1 + L 2 + L 3 … In Parallel circuits: L t = L 1 x L 2 L 1 + L 2

Inductor Summary Inductors store electrical energy in their magnetic fields. Inductors are additive in series, “reciprocal of sum of reciprocals” in parallel. Inductors tend to pass DC currents and block AC currents. The unit of measurement for inductors is the Henry (H).

Capacitors

Capacitors A capacitor is made by separating two conductive plates by an insulator or dielectric. Capacitors store electrical energy in an electrostatic field. Capacitors tend to block DC and pass AC

Capacitors Remember: Like charges repel. Current will flow only until one plate is full of negatively charged electrons the other has almost none. This creates a difference of potential (a voltage) across the plates almost like a battery.

WARNING WARNING! CAPACITORS CAN HOLD A CHARGE FOR QUITE SOME TIME. Theywould be very happy to bite you. They would be very happy to bite you.

Capacitors The Value of a capacitor can be varied by: Increasing/decreasing the plate area Increasing/decreasing the plate spacing Changing type of dielectric material The unit of measurement is the Farad (F).

Adding Capacitors Capacitors add in parallel C t = C 1 + C 2 + C 3 … In Series C t = C 1 x C 2 Note: This is backwards from resistors and inductors! C 1 + C 2

Capacitor Summary Capacitors store electrical energy in their electrostatic fields. Capacitors are additive in parallel, “reciprocal of sum of reciprocals” in series. Capacitors tend to pass AC currents and block DC currents. The unit of measurement for capacitors is the Farad (F).

The Fuse Fuse Fuse

The Fuse A fuse will self destruct when current flow exceeds the fuse rating. This results in an open condition, and current flow will then cease, saving equipment from overheating and possible fire damage.

What electrical component is used to protect other circuit components from current overloads? A. Fuse B. Capacitor C. Shield D. Inductor

What type of component is often used as an adjustable volume control? A. Fixed resistor B. Power resistor C. Potentiometer D. Transformer

What is the approximate amount of change, measured in decibels (dB), of a power increase from 5 watts to 10 watts? A. 2 dB B. 3 dB C. 5 dB D. 10 dB

What electrical component stores energy in an electric field? A. Resistor B. Capacitor C. Inductor D. Diode

Intermission

Practical Circuits Putting it all together.

Filters We have learned: Capacitors tend to pass AC and high frequencies Inductors tend to pass DC and low frequencies We can now build circuits that… Block transmission of harmonic radiation Block reception of amateur frequencies Pass only a desired group of frequencies Note the output of each type of filter.

What instrument other than an SWR meter could you use to determine if a feedline and antenna are properly matched? A. Voltmeter B. Ohmmeter C. Iambic pentameter D. Directional wattmeter

Why is coaxial cable used more often than any other feedline for amateur radio antenna systems? A. It is easy to use and requires few special installation considerations B. It has less loss than any other type of feedline C. It can handle more power than any other type of feedline D. It is less expensive than any other types of feedline

12 3 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? A. A balanced modulator B. A transmit-receive switch C. A power amplifier D. A high-pass filter

What type of filter should be connected to a TV receiver as the first step in trying to prevent RF overload from a nearby 2 meter transmitter? A. Low-pass filter B. High-pass filter C. Band-pass filter D. Band-reject filter

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

Signals and Emissions AM/FM, SSB, CW Alphabet Soup! Right: W4ZH J. Smith in New Orleans testing HF Voice and HF

FCC Emission Types CWDataPhoneTest MCWRTTYImagePulse SS (Spread Spectrum)

CW In CW the telegraph key simply turns the radio transmitter on and off to form the Morse code characters

CW and MCW CW (continuous wave) is the on-off keying of a radio signal generally used for Morse code MCW is the tone modulation of a carrier wave made to sound like Morse code, as in the automatic identifiers used on some repeaters.

Phone Phone is any voice transmission This includes AM (amplitude modulation) SSB (single side band, similar to AM) FM (frequency modulation)

Amplitude Modulation An unmodulated RF carrier wave A carrier wave AM modulated with a simple audio tone

AM and SSB An unmodulated RF carrier requires narrow bandwidth Modulation of the carrier creates sidebands. This requires more bandwidth. Transmitter power is spread across this bandwidth

AM and SSB The carrier contains no audio information. The sidebands contain duplicate audio information By filtering out the carrier and one sideband, we save spectrum and concentrate our RF energy into a narrower bandwidth. SSB is therefore more efficient.

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

AMvs.SSB Sounds really nice Inexpensive Simpler equipment More efficient. Further range based on same output power. Narrower bandwidth, more room on crowded bands. All modern HF radios support SSB (not all support AM)

AM and SSB When SSB is not modulated (when you are not talking) the transmitter output power drops to almost nothing. When either AM or SSB is over- modulated the signal may cause “splatter,” and interfere with other stations.

Frequency Modulation Unmodulated carrier, full power at all times Waveform of modulating signal Modulated carrier with frequency deviation and constant amplitude

Frequency Modulation FM transmitters operate at full power at all times, even when you are not talking. When an FM transmitter over- modulates, the transmitted signal becomes so wide (bandwidth) it may interfere with adjacent channels. This is called over-deviation.

Image Image transmissions include all modes that will produce a picture, either video or paper copy (like a FAX) at the receiver. These modes include: SSTV (slow scan television) ATV (amateur television) FAX (facsimile)

Image A sample amateur SSTV transmission. A sample amateur SSTV transmission.

Image Amateurs like to receive weather images direct from the satellites. The equipment is inexpensive and you don’t even need a license!

Questions?