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So its not actually a 1MW transmitter, its 330KW, but since the antenna is not omni and somewhat directional, it has 1MW "Effective Radiated Power". Which reall

So its not actually a 1MW transmitter, its 330KW, but since the antenna is not omni and somewhat directional, it has 1MW "Effective Radiated Power". Which really means how much power it would need to have if it was a true omni antenna to have the same coverage. Sort of like saying a flashlight is 100W because its as bright as a 100W bulb when looking right into it even if the flashlight itself is only putting out 30W, the reflectors in the flashlight direct the 30W of light in one direction making it brighter. The gain listed on antennas is really just telling you how directional it is, any gain above 0 means it has directionality over a perfect omni and must be oriented properly to take advantage of it.

jtbayly 4y ago
Thank you for that last paragraph. This is very helpful to know.
- ac29 4y ago
  In this case, its not true though - the gain on this sort of FM broadcast antenna should be uniform in all horizontal directions. The gain is from reducing power in the vertical plane (that is, less energy radiated up into space and down into the ground). Orientation thus shouldnt matter. Antennas with a non-uniform horizontal radiation pattern do need to be correctly oriented. A simple example of a directional antenna is a Yagi, where more energy comes out the front than the back and sides.
  - SigmundA 4y ago
    I would nitpick that it needs to be correctly orientated such that it's perpendicular to the horizon. This is of course convenient to do but is important when placing your own smaller antennas vs say putting them at off angles or parallel to the horizon. Many small antennas like say for cellular use will list large gain numbers, and many people will buy based one having more gain than another. The ones with more gain typically have radiation patterns less uniform than a dipole and may pick up better to certain sides, even though they aren't an obvious single direction antenna like a Yagi or marketed as such.
    - ac29 4y ago
      > I would nitpick that it needs to be correctly orientated such that it's perpendicular to the horizon This is of course true! I wish it didnt need to be said, but I work in radio and I have absolutely seen people install antennas incorrectly (installing Yagi antennas with the wrong polarity or facing the wrong direction is reasonably common). Hopefully that wouldnt be an issue at FM broadcast sites though.
ac29 4y ago
> The gain listed on antennas is really just telling you how directional it is, any gain above 0 means it has directionality over a perfect omni and must be oriented properly to take advantage of it. This is generally correct, but for more context ERP uses a gain in dBd which is decibels relative to a dipole antenna. A dipole is not a perfect omnidirectional antenna. A perfectly omnidirectional antenna would be an isotropic or point source antenna, which is only theoretical (no truly isotropic antenna can actually be built as far as I know, but dipoles are simple to build and widely used). Gain is measured in dBi when comparing to isotropic antennas, and EIRP (Effective Isotropic Radiated Power) would be used, not ERP. This may sound like a small nitpick, but its a pretty huge difference in practice! 1MW ERP is approximately 1.6MW EIRP.
- SigmundA 4y ago
  Thanks for the correction, a dipole has more of a doughnut radiation pattern vs the perfect sphere of an isotropic giving directionality perpendicular to the antenna. A theoretical perfect dipole has 2.15 dBi gain over the perfect theoretical isotropic, but again only in certain directions. Perhaps the article would have been even more impressive titled 1.6 MW transmitter then just listing EIRP down in the article instead of ERP. Either way its actually only a 330KW transmitter.

jtbayly 4y ago

Thank you for that last paragraph. This is very helpful to know.

ac29 4y ago
In this case, its not true though - the gain on this sort of FM broadcast antenna should be uniform in all horizontal directions. The gain is from reducing power in the vertical plane (that is, less energy radiated up into space and down into the ground). Orientation thus shouldnt matter. Antennas with a non-uniform horizontal radiation pattern do need to be correctly oriented. A simple example of a directional antenna is a Yagi, where more energy comes out the front than the back and sides.
- SigmundA 4y ago
  I would nitpick that it needs to be correctly orientated such that it's perpendicular to the horizon. This is of course convenient to do but is important when placing your own smaller antennas vs say putting them at off angles or parallel to the horizon. Many small antennas like say for cellular use will list large gain numbers, and many people will buy based one having more gain than another. The ones with more gain typically have radiation patterns less uniform than a dipole and may pick up better to certain sides, even though they aren't an obvious single direction antenna like a Yagi or marketed as such.
  - ac29 4y ago
    > I would nitpick that it needs to be correctly orientated such that it's perpendicular to the horizon This is of course true! I wish it didnt need to be said, but I work in radio and I have absolutely seen people install antennas incorrectly (installing Yagi antennas with the wrong polarity or facing the wrong direction is reasonably common). Hopefully that wouldnt be an issue at FM broadcast sites though.

ac29 4y ago

> The gain listed on antennas is really just telling you how directional it is, any gain above 0 means it has directionality over a perfect omni and must be oriented properly to take advantage of it. This is generally correct, but for more context ERP uses a gain in dBd which is decibels relative to a dipole antenna. A dipole is not a perfect omnidirectional antenna. A perfectly omnidirectional antenna would be an isotropic or point source antenna, which is only theoretical (no truly isotropic antenna can actually be built as far as I know, but dipoles are simple to build and widely used). Gain is measured in dBi when comparing to isotropic antennas, and EIRP (Effective Isotropic Radiated Power) would be used, not ERP. This may sound like a small nitpick, but its a pretty huge difference in practice! 1MW ERP is approximately 1.6MW EIRP.

SigmundA 4y ago
Thanks for the correction, a dipole has more of a doughnut radiation pattern vs the perfect sphere of an isotropic giving directionality perpendicular to the antenna. A theoretical perfect dipole has 2.15 dBi gain over the perfect theoretical isotropic, but again only in certain directions. Perhaps the article would have been even more impressive titled 1.6 MW transmitter then just listing EIRP down in the article instead of ERP. Either way its actually only a 330KW transmitter.