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24 Cards in this Set
- Front
- Back
- 3rd side (hint)
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How fast do radio waves travel through space? |
Speed of Light |
Quick! |
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How many times around the world in ONE SECOND could a radio wave go? |
7 |
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What is signal polarisation? |
The direction which the wave goes, e.g. horizontal or vertical. |
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What is wavelength? How is frequency determined? What is frequency measured in? |
Wavelength is the length of a wave aka cycle
Frequency is the number of waves passing per second
The measurement is usually Hertz |
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What is amplitude? What happens if amplitude is high? |
The measurement of the peaks or troughs from middle value (the ‘height’ of the wave)
The greater the amplitude the better the signal |
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What is modulation? What are the three most common ways of transmitting info on the carrier wave? |
Creating variation in the amplitude, frequency or phase of radio waves to transmit intelligence.
Keying on and off - Morse Amplitude modulation (AM) Frequency modulation (FM) |
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How does amplitude modulation radio work? What does a higher modulation depth mean for signal? What if the band is over modulated? |
The frequency stays the same but the intelligent audio wave mixes with the carrier wave and makes the amplitude bigger. Higher depth - or more amplitude creates a stronger signal while over modulation will create reception distortion. |
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What are side bands? How many sidebands does AM signals have? How can you conserve bandwidth and power? What is the downside to doing this? |
They are extra frequencies either side of a modulated AM band, they are used to receive intelligent information. An AM receiver will therefore have to be able to tune in to a few frequencies either side of the carrier that has been tuned in. AM signals have 2 sidebands, an upper side band (USB) that transmits the carrier + audio and a lower side band (LSB) that transmits carrier wave minus audio. To conserve bandwidth and power use a single sideband (SSB) this improves transmission economy by eliminating high energy AM carrier. HF radios are SSB. Their main disadvantage is they require fine tuning due to narrow bandwidth. |
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How do you achieve FM? What are the benefits of FM transmitters? What are downsides of FM? How many sidebands to transmit FM? What is bandwidth? |
By adjusting the frequency instead of the amplitude.
FM transmitters have are simpler, use less power and are static free
Downsides include: receivers are more complex, much more bandwidth required than AM
Many sidebands required for transmission Bandwidth is the amount of frequency spectrum required to transmit the intelligence - the more intelligence and greater the quality, the greater bandwidth required. Having less bandwidth means needing greater distance between channels to avoid interference. |
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Radio waves propagate in 2 ways what are they? |
1) Ground waves - travel along earths surface can be either: Direct waves - go pretty direct from transmitter to receiver Surface waves follow the curvature of the earth from diffraction.
2) Sky waves - have been refracted and reflected by the ionosphere back to earths surface |
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Why may signals be out of phase? What do out of phase signals cause? |
Can be out of phase if they’ve taken different paths- some sky some ground
Out of phase can cause fading or signal loss |
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What is attenuation? Which frequencies suffer from it the most? |
It is the absorption and weakening of a signal by the surface over which it’s travelling. Lower frequencies suffer less attenuation so can stay stronger over longer distances |
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What are the VHF rated coverages? |
0-5000 : 60nm 5-10: 90 10-15: 120 15-20: 150 20+: 180 |
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What surfaces are best for radio waves to travel over? What are the worst with worst attenuation? |
Best - water Worst sand, snow and ice |
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What are the VHF rated coverages? |
0-5000 : 60nm 5-10: 90 10-15: 120 15-20: 150 20+: 180 |
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What surfaces are best for radio waves to travel over? What are the worst with worst attenuation? |
Best - water Worst sand, snow and ice |
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How do I calculate the theoretical range of a VHF signal with a formula? Where is this assuming the transmitter is? What if transmitter is higher? |
✔️(1.5Xreciever altitude in feet) E.g receiver at 5000ft means the square root of 1.5x5000 Equals 86.6nm This assumes transmitter is at sea level. If it’s higher then do the calculation twice - one for the height of the receiver and one for the transmitter then ADD those two answers together. |
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How do I calculate the theoretical range of a VHF signal with a formula? Where is this assuming the transmitter is? What if transmitter is higher? |
✔️(1.5Xreciever altitude in feet) E.g receiver at 5000ft means the square root of 1.5x5000 Equals 86.6nm This assumes transmitter is at sea level. If it’s higher then do the calculation twice - one for the height of the receiver and one for the transmitter then ADD those two answers together. |
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Why do NDB’s have individual rated coverages? |
Because the radio waves tend to travel on many different paths. Whereas VHF tend to work only on line of sight |
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Why are NDB rated coverages reduced at night? |
Because of the increased sky wave interference at night due to the higher ionosphere |
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The signals leaving a HF transmitter tend to split into two parts, what are they? How far do they each go? What’s the special name for one of them? Which frequencies tend to work best at night? |
They split into a ground wave, only travels around 100nm, the other part is a sky wave which travels out towards space then gets reflected by the ionosphere back down to earth. The distance it travels is called Skip distance. Higher frequencies better for day, lower for night. |
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What is the point of electrical bonding in an aircraft? |
A buildup of static electricity can affect radio reception. The static electricity can build up because of the air molecules passing over the airframe, also nearby thunderstorms can cause electrical interference. We want an even electrical potential between different parts of the airframe |
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What kind of modulation do aircraft comms use? |
AM - amplitude modulation |
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What are the advantages of using sidebands? |
Less external noise and interference The carrier wave doesn’t need to be as powerful Can transmit different info simultaneously on both bands |
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