# 2013 Week 2: Radio Signals and Fundamentals

This is the class outline for week 2 of the SCARS Technician class 2013.

## Quiz on Week 1 Handout

1. 3.75 MHz is the same as
1. 3750 Hz
2. 375 kHz
3. 3750 kHz
4. 0.0375 GHz
2. If you QSY up 250 Hz from 7150 kHz, you’d be at
1. 7150.25 kHz
2. 7400 kHz
3. 7150.250 kHz
4. A. and C.
3. An ordinary AA battery is about 1.5 volts, or
1. 150 millivolts
2. 1500 megavolts
3. 1500 mV
4. 150 mV
4. For both question 1. and 2., you are operating in what part of the EM spectrum?
1. LF
2. HF
3. VHF
4. UHF
5. Which of the following modes makes most efficient use of the RF spectrum?
1. AM
2. FM
3. CW
4. SSB
6. Which of the following modes is most efficient for voice communications?
1. AM
2. FM
3. CW
4. SSB
7. About how much bandwidth does that mode require?
1. 3 kHz
2. 6 kHz
3. 3 MHz
4. 6 MHz
8. Fast-scan TV (video) requires about 6 MHz of bandwidth. Why do you think it is impractical in the HF part of the spectrum?

# Chapter 2: Radio Signals and Fundamentals

• alternating current (AC) in wire (“antenna”) creates time-varying electric (E) field around wire
• time-varying E field creates magnetic field (M)
• time-varying M field creates E field • EM waves travel through vacuum (~air) at speed of light:
• C = 300,000,000 m/s
• different frequency EM waves have different properties:   – approx. 3 kHz to 300 GHz

### Characteristics of Waves

• Amplitude
• Frequency
• Period
• Wavelength
• Harmonics ## Frequency and Wavelength

Frequency: number of cycles (peak to peak, trough to trough…) per second = Hertz = Hz (cps)

• kHz, MHz, GHz

Wavelength: length, in meters, of one full wave in space (peak to peak, trough to trough…)
Since C is constant,

• f = C/λ or
• λ=C/f

The higher the frequency, the shorter the wavelength!
The lower the frequency, the longer the wavelength!

For frequency in Hz, distance in m, time in s (fundamental metric units), then,

• f = 300,000,000/λ or
• λ = 300,000,000/f

So, if you are operating in the 15 m band, the approximate frequency would be:

• f = 300,000,000/15 = 20,000,000 Hz

For convenience [by dividing both sides of the equation above by 1,000,000] we can use:

• f = 300/λ

where f is in MHz
Similarly,

• λ = 300/f

Our problem above becomes:

• f = 300/15 = 20 MHz

#### T3B07 What property of radio waves is often used to identify the different frequency bands?

1. The approximate wavelength
2. The magnetic intensity of waves
3. The time it takes for waves to travel one mile
4. The voltage standing wave ratio of waves

Because band implies a range of frequencies, band “names” are approximate. For example, if you are operating at 7150 kHz, what band are you in?300/7150 = 0.04196 meters Whoops!

## Modulation and Bandwidth

### Continuous Wave

• the simplest type of radio signal is a continuous wave,, or an unmodulated wave, or a single frequency: • A continuous wave takes up virtually no bandwidth, or “space” in the radio spectrum: • this is what a spectrum analyzer would see
• the simplest way to modulate a wave is to turn it on and off, such as with Morse code
• hams call this CW (although the continuous wave is interrupted) ### Amplitude Modulation  ### Single-Sideband (SSB) Modulation • Below 10 MHz: LSB
• Above 10 MHz: USB
• At 10 MHz: WWV!

### Frequency Modulation (FM) • narrow-band FM
• wide-band FM

### Comparing Modulations ### Basic Station ### Station with Accessories ### Repeater Station ## “Homework” for next week 