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more notes on antennas

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Thomas Bishop 2026-02-01 18:55:58 +00:00
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@ -103,3 +103,32 @@ Some example calculations:
| 6dB | x4 | 10 watts | 40 watts | | 6dB | x4 | 10 watts | 40 watts |
| 9dB | x8 | 10 watts | 80 watts | | 9dB | x8 | 10 watts | 80 watts |
| 10dB | x10 | 10 watts | 100 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.
## Antenna polarisation
**Polarisation** means whether the antenna is positioned on a vertical or
horizontal plane.
Of the antennas covered at foundation level, only dipoles and Yagis can be
positioned at variable polarities.
VHF and UHF are received most effectively when the transmitter and receiver have
the same antenna polarisation.