56 lines
1.6 KiB
Markdown
56 lines
1.6 KiB
Markdown
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---
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tags: [radio, ham-study]
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---
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EMC or _Electromagnetic Compatibility_ is concerned with avoiding interference
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between different pieces of electronic equipment.
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> Interference is the degradation or disruption of a desired radio signal caused
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> by unwanted electromagnetic energy. It can manifest as static, noise, signal
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> loss, or distorted audio.
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Transmitters can _cause_ interference. Receivers can suffer _from_ inteference.
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**The more power a station uses, the more likely it is to cause interference.**
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**Immunity** is the ability of a piece of equipment to function correctly in the
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presence of strong RF signals.
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Different transmission modes are more or less likely to cause interference.
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AM and SSB are more likely to cause interference.
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FM and some HF data modes are least likely (remember "Friendly Modulation").
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## Occurences of interference
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Nearby radio transmissions can cause interference to:
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- domestic mains wiring
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- TV aerial leads
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- Speaker leads
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- Telephone wiring
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- Internal circuitry
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## Methods of reducing interference
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- Fitting **filters** (known as **chokes**) in mains or antenna leads as close
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to the affected device as possible
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- Using balanced antennas at HF
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- Using horizontal dipoles
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- Avoiding the use of end-fed antenna types
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- Siting antennas as far from houses as possible and as high as pissible
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- Using a dedicated RF earth to prevent RF current from entering the mains earth
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system
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## Dummy loads
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A dummy load is a screened resistor attached to a transmitter instead of an
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aerial. This enables the transmitter to operate without putting out a signal
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which can be useful when detecting and managing interference.
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