howto:hambasics:sections:practice
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howto:hambasics:sections:practice [2020/10/07 08:09] – va7fi | howto:hambasics:sections:practice [2020/10/24 16:59] – va7fi | ||
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====== Receivers ====== | ====== Receivers ====== | ||
- | There are three main characteristics of a receiver: sensitivity, | + | There are three main characteristics of a receiver: |
===== Sensitivity ===== | ===== Sensitivity ===== | ||
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* If SNR < 1, then the noise is stronger than the signal. | * If SNR < 1, then the noise is stronger than the signal. | ||
- | Like other ratios, we often express SNR in [[howto: | + | Like other ratios, we often express SNR in [[howto: |
* If SNR > 0 dB, then the signal is stronger than the noise. | * If SNR > 0 dB, then the signal is stronger than the noise. | ||
* If SNR = 0 dB, then the signal and the noise have the same strength. | * If SNR = 0 dB, then the signal and the noise have the same strength. | ||
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<WRAP center box 90%> | <WRAP center box 90%> | ||
- | {{ :howto: | + | {{ howto: |
</ | </ | ||
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* FM, needs about 20 kHz, which is why FM radio stations sound better than AM radio stations. | * FM, needs about 20 kHz, which is why FM radio stations sound better than AM radio stations. | ||
- | {{ | + | {{ scope01.png |
Now back to the receiver. | Now back to the receiver. | ||
+ | ==== Filters ==== | ||
+ | Sometimes a specific noise or interference is mixed in the signal and we'd like to reduce or eliminate it. One way is to use filters. | ||
+ | * A filter that lets high frequencies through but blocks low frequencies is called a //high pass// filter. | ||
+ | * A filter that lets low frequencies through but blocks high frequencies is called a //low pass// filter. | ||
+ | * Combining a high pass and low pass filter we get a //band pass// filter, which lets audio between two frequencies. | ||
+ | * The " | ||
+ | {{ notch1a.png }} | ||
+ | |||
+ | This picture has three main parts. | ||
+ | - The frequency is 7.100 MHz on LSB. | ||
+ | - The scope shows this frequency relative to the entire band (7.000 Mhz to 7.300 Mhz) | ||
+ | - At the bottom is the audio spectrum of what we hear (with a 2.4 kHz band pass filter). | ||
+ | |||
+ | You'll notice that there' | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | {{notch2.png? | ||
+ | </ | ||
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======= Questions ======= | ======= Questions ======= | ||
- | * B-003-009-001 -> B-003-008-006 | + | * B-003-010-001 -> B-003-011-001 |
[[stationassembly |{{/ | [[stationassembly |{{/ | ||
howto/hambasics/sections/practice.txt · Last modified: 2020/12/30 09:08 by va7fi