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.
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.
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.
> 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.
> 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.
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.
The coax and transmission stuff all had to be engineered for safety and regulatory compliance. two wet pieces of string can carry an ethernet signal, and nobody can stop you.
> These units must perform a bit of magic, combining multiple RF signals relatively near each other on the FM band, into one roughly 300,000 kW FM signal at the end, output in a 9" coax line that gets switched into a tuned 8-bay antenna 1115 ft (340 m) above the earth.
300 thousand kilowatts? (300 MW?) No wonder they need such massive cooling.
The most telling image to me is that one with the meter indicating reflected power in kilowatts. If they employ any kind of automatic antenna tuning, I'd be curious to see its internals.
The videos they do are very interesting too, though I prefer the write-up for more thoughtful consumption. I would love to see more behind the scenes tours of interesting commercial or industrial sites by their engineers. Anyone have a good collection of these?
Great tour of that tower site, and a nice analysis of the requirements of transmitting both analogue and digital signals. For international readers, the digital radio standard of North America is the completely proprietary HD Radio (Hybrid Digital) IBOC (In-Band-On-Channel) system owned by DTS (nee iBiquity). The DAB system used outside of North America is incompatible. Automobiles built for the North American market now tend to come with HD Radio reception as standard equipment.
As a proprietary system, HD Radio involves costs that can be prohibitive to small broadcasters. I do not know of any attempts to reverse-engineer the HD Radio system, nor am I qualified to guess at the workload involved, but an open license alternative is a nice dream that would enable a huge quality and capability improvement for even the smallest radio stations.
For receivers at least, you can use some open source software to decode HD radio using an SDR, but the market for open source transmitter software is almost infinitesimally smaller. Plus it would be much easier to find and punish a station transmitting HD without a license.
I know my Dad has a lot of experience on both sides of the licensing (both large radio conglomerates and smaller independent broadcasters) and I think having a discussion on the history and implementation of HD Radio in the US could make a good follow-up video at some point.
> it would be much easier to find and punish a station transmitting HD without a license
If I'm understanding you, a clean sheet implementation of "HD Radio-compatible" digital broadcasting using open source and open hardware techniques over a federally licensed station would contravene the proprietary system's license?
Unfortunately proving that nothing is infringing on whatever patents Ibiquity created would likely be difficult and/or expensive, and since most indie broadcasters are still happy to just broadcast analog-only for the time being, there's not a lot of will to fight for it.
A lot of the ibiquity patents are expiring this year or have already expired as well. I haven't been following the patent situation on this as closely as I used to, but needless to say I will be very excited when they all finally expire. Digital radio would have been awesome had it become pervasive in the late 90's when it should have.
Yeah, though if you really want reliability through one piece of equipment it'll be something with dual parallel a+b 48v power feeds and hotswap fan modules.
Indeed, something cool about that is that transmitter combined FM for the analog stereo audio, and AM for the analog TV signal!
You also get to look inside an old tube transmitter; all the ones I've seen these days are solid state, though in our second video I did mention a couple tubes they had at the site they now use as doorstops!
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[ 3.3 ms ] story [ 61.7 ms ] threadSort 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.
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.
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.
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.
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.
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.
300 thousand kilowatts? (300 MW?) No wonder they need such massive cooling.
Imagine trying to screw one of those into your cable modem!
As a proprietary system, HD Radio involves costs that can be prohibitive to small broadcasters. I do not know of any attempts to reverse-engineer the HD Radio system, nor am I qualified to guess at the workload involved, but an open license alternative is a nice dream that would enable a huge quality and capability improvement for even the smallest radio stations.
I know my Dad has a lot of experience on both sides of the licensing (both large radio conglomerates and smaller independent broadcasters) and I think having a discussion on the history and implementation of HD Radio in the US could make a good follow-up video at some point.
If I'm understanding you, a clean sheet implementation of "HD Radio-compatible" digital broadcasting using open source and open hardware techniques over a federally licensed station would contravene the proprietary system's license?
https://github.com/argilo/gr-nrsc5
A lot of the ibiquity patents are expiring this year or have already expired as well. I haven't been following the patent situation on this as closely as I used to, but needless to say I will be very excited when they all finally expire. Digital radio would have been awesome had it become pervasive in the late 90's when it should have.
You also get to look inside an old tube transmitter; all the ones I've seen these days are solid state, though in our second video I did mention a couple tubes they had at the site they now use as doorstops!