49 lines
1.8 KiB
Markdown
49 lines
1.8 KiB
Markdown
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---
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tags: [radio, ham-study]
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---
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[Antennas](./Types_of_antenna.md) like the Yagi have **gain**. This means they
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can increase the power that they receive from the transmitter via the
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[feeder](./Feeders.md).
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Gain is measured in decibels:
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| Antenna gain | Power muliplied by a factor of... |
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| ------------ | --------------------------------- |
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| 3dB | 2 |
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| 6dB | 4 |
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| 9dB | 8 |
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| 10dB | 10 |
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ERP is the **Effective Radiated Power**. This is the product of the power that
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the antenna is receiving from the feeder and the gain level.
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> ERP (Watts) = power feed x antenna gain
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Some example calculations:
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| Gain | Gain times | Power to antenna | ERP |
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| ---- | ---------- | ---------------- | --------- |
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| 3dB | x2 | 10 watts | 20 watts |
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| 6dB | x4 | 10 watts | 40 watts |
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| 9dB | x8 | 10 watts | 80 watts |
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| 10dB | x10 | 10 watts | 100 watts |
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### ERIP
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ERP is calculated relative to the half-wave dipole. This is the benchmark. The
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power that would be generated using this type of antenna.
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But, as noted above, the dipole has a distinct radiation pattern - diffusing in
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poles at right angles to the horizontal plane of the antenna.
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By being tied to the dipole, ERM is therefore not the most universal or
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objective unit of measurement.
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To remedy this, there is another unit: ERIP. This stands for **Effective
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Isotropic Radiated Power**. It's the same calculation but it uses a theoretical
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antenna that would radiate equally in all directions as the benchmark.
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Because of the equal radiation pattern in all directions, EIRP will always be
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higher than ERP. Roughly speaking, 10 Watts in EIRP would be 6 Watts in ERP.
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