General engineering question: Why do ERP levels vary and what are the?

[fordranger797]

Sort of.

One bay is essentially a radiator that "sends" the signal on a full 180° arc from ground to straight up. That means that much of the power goes at upwards angles into the sky... like a normal light bulb.

When you add more elements, the beam of the signal changes from the light bulb to more of a spotlight. The more bays, the tighter the beam. In other words, it is the same amount of power, but aimed at the market area towards the horizon, with less low angle "undershoot" or high angle "star shooting".

In these cases, the elements are "stacked" vertically. The spacing between bays is also a consideration for gain and beam angle.

When you get over 6 bays in an antenna ("antenna" being the system, "bays" being the individual radiating elements of the antenna system) there begin to be artifacts which cause the signal beam to have nulls and spikes; the beam can be so narrow that significant areas are under- or over-shot. This is particularly noxious with some 10 to 12 bay antennas, but most stations do not use that many bays anymore.

Many engineers prefer low bay count. When a station is lower powered, like an A, two bays would be considered optimal, and perhaps four to six bays for higher powers. In installations I have worked on, I have stayed at 6 or under.

These considerations change when panel antenna systems (such as in common antenna systems used by many stations) are employed. Panels are arranged in a circle around a central point on a structure, instead of being stacked vertically and are subject to different radiation "beam" calculations.

This is very, very simplified.

Beam me up, Scotty.

Thank you, David,very helpful as always. Think that i'm ready to become an engineer?

 

[davideduardo]

Thank you, David,very helpful as always. Think that i'm ready to become an engineer?

Stay away from the high voltage for a while more!

If you are interested in knowing a bit more about the technical side, try to get a copy of the NAB's "A Broadcast Engineering Tutorial for Non-Engineers" on eBay or a used book dealer like Abe Books. It is a fairly good primer about the subject.

 

[fordranger797]

Stay away from the high voltage for a while more!

If you are interested in knowing a bit more about the technical side, try to get a copy of the NAB's "A Broadcast Engineering Tutorial for Non-Engineers" on eBay or a used book dealer like Abe Books. It is a fairly good primer about the subject.

Okay, will do! And I certainly will look into that book. Not saying that I would ever take the steps to become an engineer, but this field in radio has always interested me and i'm still plenty young enough to learn more about it.

 

[fordranger797]

The master FM antennæ in New York and Chi-town are probably one or two bays because much of the market is down.
On the other hand, the towers between Dallas and Fort Worth and between Miami and Fort Lauderdale are fairly remote and not on mountains, so theirs are a lot bigger.
(definitely for Miami except for size restrictions or height requirements, and Probably for Dallas)

I take it you mean that the market is mainly LOS from the tower, and not a great deal of power needs to be aimed towards the horizon (but I may have misinterpreted).

 

[davideduardo]

Okay, will do! And I certainly will look into that book. Not saying that I would ever take the steps to become an engineer, but this field in radio has always interested me and i'm still plenty young enough to learn more about it.

A knowledge of how things work never hurts.

When I was building my first station, I found that nobody in the market know what cartridge tape gear was for, and had never seen anything like an Audimax and Volumax. So I ended up taking correspondence courses and learned enough engineering to build my own studio and set up the audio processing. As you said, it's a good thing to learn early in your career.