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tags: [radio, ham-study]
---

[Antennas](./Types_of_antenna.md) like the Yagi have **gain**. This means they
can increase the power that they receive from the transmitter via the
[feeder](./Feeders.md).

Gain is measured in decibels:

| Antenna gain | Power muliplied by a factor of... |
| ------------ | --------------------------------- |
| 3dB          | 2                                 |
| 6dB          | 4                                 |
| 9dB          | 8                                 |
| 10dB         | 10                                |

ERP is the **Effective Radiated Power**. This is the product of the power that
the antenna is receiving from the feeder and the gain level.

> ERP (Watts) = power feed x antenna gain

Some example calculations:

| Gain | Gain times | Power to antenna | ERP       |
| ---- | ---------- | ---------------- | --------- |
| 3dB  | x2         | 10 watts         | 20 watts  |
| 6dB  | x4         | 10 watts         | 40 watts  |
| 9dB  | x8         | 10 watts         | 80 watts  |
| 10dB | x10        | 10 watts         | 100 watts |

### ERIP

ERP is calculated relative to the half-wave dipole. This is the benchmark. The
power that would be generated using this type of antenna.

But, as noted above, the dipole has a distinct radiation pattern - diffusing in
poles at right angles to the horizontal plane of the antenna.

By being tied to the dipole, ERM is therefore not the most universal or
objective unit of measurement.

To remedy this, there is another unit: ERIP. This stands for **Effective
Isotropic Radiated Power**. It's the same calculation but it uses a theoretical
antenna that would radiate equally in all directions as the benchmark.

Because of the equal radiation pattern in all directions, EIRP will always be
higher than ERP. Roughly speaking, 10 Watts in EIRP would be 6 Watts in ERP.