Test Equipment • Voltmeter - an instrument that is used to measure voltage. • Ammeter - an instrument used to measure amperage in a circuit. • Multimeter - combines the functions above with resistance and others to make a versatile piece of test equipment. Wattmeter - a device that measures power coming from a transmitter through the antenna feed line. A directional wattmeter measures forward and reflected power. Wattmeters generally are useful in certain frequency ranges Signal Generator - a device that produces a stable, adjustable low level signal (AF or RF). It can be used to tune circuits. • • – It is used in parallel with a circuit to be measured. – a series resistor extends the range of the meter. – It is hooked up in series with the circuit to be tested. – A shunt resistor (in parallel w/meter) extends the range of the meter. PHYS 401 Physics of Ham Radio 61 Chapter 2 (T3, T8) • Radio and Signal Fundamentals • Modulation • Radio Equipment Basics PHYS 401 Physics of Ham Radio 62 Electromagnetic Spectrum PHYS 401 Physics of Ham Radio 63 Frequency and Wavelength • • • • • Frequency is measured in cycles per second. The unit of frequency is Hertz (Hz) Audio frequency is 20 Hz to 20,000 Hz (20 kHz) Radio frequency is above 20,000 Hz (20 kHz) Radio frequency and wavelength are related: – c = f (Hz) x λ (meters) – c (speed of light) = 3 x 108 m/sec – λ (meters) = 300 / f (MHz) PHYS 401 Physics of Ham Radio 64 Frequency and Wavelength • • • • • Frequency is measured in cycles per second. The unit of frequency is Hertz (Hz) Audio frequency is 20 Hz to 20,000 Hz (20 kHz) Radio frequency is above 20,000 Hz (20 kHz) Radio frequency and wavelength are related: – c = f (Hz) x λ (meters) – c (speed of light) = 3 x 108 m/sec – λ (meters) = 300 / f (MHz) PHYS 401 Physics of Ham Radio 65 Frequency and Wavelength • Harmonics – at multiples of the fundamental frequency. PHYS 401 Physics of Ham Radio 66 Frequency and Wavelength • Harmonics – at multiples of the fundamental frequency. • RF = Radio Frequency (all) • VLF = 3-30 KHz • LF = 30 – 300 KHz • MF = 300 KHz- 3 MHz • HF = 3-30 MHz • VHF= 30-300 MHz • UHF = 300 MHz – 3 GHz • SHF = 3 GHz – 30 GHz • EHF = 30 GHz – 300 GHz PHYS 401 Physics of Ham Radio 67 Modulation • To transmit information we must modulate a radio signal. That means to vary the radio wave’s frequency, phase or amplitude. • Radio frequencies can be generated by : – crystal oscillators – variable frequency oscillators PHYS 401 Physics of Ham Radio 68 Continuous Wave (CW) • CW is a communications mode transmitted by off/on keying of an RF signal. • The coding of the is called the International Morse code. • We sometimes say “dah” for the dash and “dit” for the dot. A dash lasts twice as long as a dot. Dit-dit-dah-dit dit-dit-dah dah-dit ! PHYS 401 Physics of Ham Radio 69 Continuous Wave (CW) PHYS 401 Physics of Ham Radio 70 Amplitude Modulation and SSB • At constant frequency, the power of the carrier is modulated in proportion to audio volume (pressure). • In the frequency domain, there are upper and lower sidebands and the carrier frequency. • Single sideband filters out all but one sideband. This puts more power to the actual modulated signal. PHYS 401 Physics of Ham Radio 71 Amplitude Modulation and SSB PHYS 401 Physics of Ham Radio 72 Frequency Modulation (FM) • The amplitude of the RF signal is held constant, but the frequency is varied in proportion to the shape of the audio wave. • FM Signals are the cleanest. They are the modulation mode of choice for VHF and UHF voice communications. • Requires a carrier higher frequency than speech! PHYS 401 Physics of Ham Radio 73 Spurious Emissions • Any signal that is emitted outside the band on which you are operating (it’s your responsibility to fix it!) • Common types include: – Parasitic oscillation (tube type amplifiers). – Removal of shields from transmitter. – Harmonics. – Splatter. •--- ••- -• -•- -• --- •• ••• • • ••• -••• •- -•• PHYS 401 Physics of Ham Radio 74 Spurious Emissions Harmonics (multiples of a given frequency) PHYS 401 Physics of Ham Radio 75 Harmonics Cause Interference • Occur at definite intervals. • Show up as interference on specific channels or as herringbone. • Use low pass filter on transmitter and high pass on TV. • You are responsible to clean up your signal. • Can be caused by multiband antennas and poorly tuned transmitters. PHYS 401 Physics of Ham Radio 76 F is the fundamental frequency, 2 is twice that frequency, etc. PHYS 401 Physics of Ham Radio 77 Receiver (Front End) Overload • Affects all channels, usually with dramatic effect. • There is nothing that can be done to the transmitter, you must prevent the signal from entering the receiver. • For cable systems, inspect for loose connections and broken shields. • For non cable systems, use a high pass filter. PHYS 401 Physics of Ham Radio 78 Spurious Emissions - Splatter • Splatter is caused by improper adjustment of the transmitter resulting in interference with nearby frequencies. • Sources could be: – talking too loud into microphone – microphone gain too high – excessive speech processing PHYS 401 Physics of Ham Radio 79 Signal Purity and Stuff • Your RF can get into the power lines as well. There are ac power line filters which can be installed. • You should also be careful of signal purity - stable in frequency and pure in tone. There are some things that you can readily hear. • Key clicks are caused by rapid rise in transmitter output. Can cause interference several kHz on either side of your frequency. They can be taken out with a key click filter. • Chirping is caused by transient voltage changes which let your frequency change slightly when keying. • Hum - can come from poorly filtered power supplies. PHYS 401 Physics of Ham Radio 80 Emissions Standards • Bandwidth - measure of how much space your signal takes up. – CW < SSB < FM • RTTY Sending Speed – 28 - 50 MHz – 50 - 222 MHz – > 222 MHz • RTTY Frequency Shift 1200 baud 19,600 baud 56,000 baud – < 50 MHz 1000 Hz – > 50 MHz No Limit • Authorized Digital Bandwidth – 50-222 MHz – 222-450 MHz 20 kHz 100 kHz PHYS 401 Physics of Ham Radio 81 Emission Types and Bandwidth • CW (continuous wave) is narrowest 250 Hz filter is useful • RTTY is next widest (about the same as CW); a 500 Hz filter is useful • SSB has a wider bandwidth, often uses a 2800 Hz filter. • FM is the widest, about 15 kHz •- •-• • -•-- --- ••- •-• -••• •- -• -•• ••• - •• --• •••• – ? PHYS 401 Physics of Ham Radio 82 Relative Bandwidths & Receiver Filters PHYS 401 Physics of Ham Radio 83 PHYS 401 Physics of Ham Radio 84 Some Other Stuff • True Forward Power = forward power reading reflected power reading. This can be used to indicate the SWR of your antenna system. • Marker generator - a high stability oscillator that produces specific frequencies which are used to calibrate receivers and transmitters. • WWV and WWVH can also be used to calibrate receivers, as well as other things. PHYS 401 Physics of Ham Radio 85