1. Radio Equipment

2. Review: On the Transmitter Side The purpose of radio communications is to transfer information from one point to another. The information to be sent is combined with a radio wave (the carrier wave). –This process is called modulation. The carrier wave (with the embedded intelligence) is then transmitted into space by the transmitting equipment.

3. Review: On the Receiver Side Once the carrier wave is received, the carrier has done its job. The carrier and intelligence are then separated (demodulation) and the carrier is discarded. The intelligence is then processed and provided to the listener as audio, video or text.

4. Building Blocks of Radio To gain a better understanding of how radio works, let’s take a look at five basic building blocks of radio. Individual components (resistors, capacitors, coils, integrated circuits, etc.) are assembled in circuits that perform basic tasks. There are five basic tasks.

5. The Five Building Blocks Oscillators – convert dc into ac. Amplifiers – increase the amplitude of ac. Rectifiers – convert ac into dc. Mixers – combine two or more ac waveforms. Filters – attenuate (reduce) the strength of unwanted signals.

6. Oscillators Crest Trough Amplitude Wave Length

8. Amplifiers

10. Rectifiers

12. The Rectifier The term rectifier is a generic term. In radio, “rectifier like” circuits are called different, more specific things including: –Demodulators –Detectors –Product Detectors –Discriminators

13. Mixers

15. The Mixer The term mixer is a generic term. In radio, “mixer like” circuits are called different, more specific things including: –Multipliers. –Modulators.

16. Filters

17. Filter Data

19. Putting it all together Using the five building blocks, “talk” your way through a receiver from the antenna to the speaker.

26. Back to Modulation Two basic types of modulation will now be discussed in detail: –Amplitude Modulation (AM) –Frequency Modulation (FM)

27. AM When the amplitude of a wave is varied in step with the amplitude of the intelligence being sent it is called amplitude modulation. –Morse code (CW) – the carrier is turned on (100% amplitude) or turned off (0% amplitude). –AM Phone – the amplitude of the carrier is continuously varied in step with the voice signal.

29. More Detailed Look at a Voice Signal When a voice signal is combined with a carrier in a mixer, the result is the sum, the difference, and the original carrier. The sum and difference parts (sidebands) are mirror images of each other.

30. SSB – Improving Efficiency Since the sidebands are mirror images, why send both? Once the sidebands are embedded on the carrier, why send the carrier? The result: Single Sideband (SSB)

32. SSB More power is available for the desired sideband. Takes up less bandwidth. The missing sideband is recreated in the receiver by using the mirror image that was transmitted to recover the intelligence. –There is, however, some missing fidelity because of all this manipulation of the waveforms. –SSB voice quality is good, but not as good as AM.

34. FM (and/or PM) When the frequency of a wave is varied in step with the amplitude of the intelligence being sent, it is called frequency modulation.

35. Trying to Over Do It Transmitting equipment is designed to modulate the carrier the most efficient amount to get the message through. –Speech processing and pre-amplification are attempts to get more “punch” to get the message through. –If improperly done, these attempts result in distortion.

36. Overmodulation/Overdeviation If you attempt to go beyond 100% amplitude modulation, nothing is gained except excessive bandwidth (splatter) and interference. –Too much speech processing (compression) may add “punch” but at the expense of intelligibility. If you attempt to go beyond 100% frequency modulation, nothing is gained except adjacent channel interference.

37. Linear Amplifiers An amplifier added between the transmitter and antenna boosts power output. Improper operation of an amplifier can lead to problems instead of improved signal strength. –Ensure they are tuned and fed properly.

38. Linear Amplifiers Neutralization of the amplifier tubes is often required to prevent the tubes from “self oscillating” and transmitting on unintended frequencies. –During neutralization, a small sample of the tube’s output is fed back into the tube’s input to cancel unwanted oscillations. –Equipment manuals will detail the neutralization procedure.

39. What is Digital Signal Processing (DSP)? Converting a continuously changing waveform (analog) into a series of discrete levels (digital)

40. What is DSP? The analog waveform is sliced into equal segments and the waveform amplitude is measured in the middle of each segment. The collection of measurements make up the digital representation of the waveform. Once the waveform is digitized, the numbers can be manipulated by computer.

41. What is DSP?

42. Converting Analog Signals into Digital Signals The device that does the conversion is called an Analog-to-Digital Converter (ADC) A device that converts digital signals to analog signals is called a Digital-to-Analog Converter (DAC)

43. RF Interference Considerations for the General Class Operator Higher power and frequency agility increases the potential for causing interference. –Fundamental overload. –Direct detection. –Harmonics. –Rectification.

44. RF Interference Mitigation Take interference concerns seriously. Operate your equipment properly. GROUNDING!