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FM Antenna Coverage

E

EngineeringDog

All-

I had an interesting discussion yesterday regarding FM antenna coverage among various manufacturers for an upcoming translator project. We were talking about various brands, and one person offered that one brand would give better coverage--reach father--than the others for the translator. I disagree and have seen no evidence to support this assertion (other than marketing). It got me thinking, so I'm curious what you think.

Let's take three manufacturers. Two common manufacturers: ERI and Jampro. And one "budget" manufacturers: PSI. For the translator project, if the three are all properly engineered for the same tower and for the same pattern, I assert that the coverage among the three will be equal, except perhaps for fractions of percentages of difference. I believe that the most important concerns are the elevation and terrain between antenna and listener. In other words, all things being equal, is there really any evidence that one brand will truly outperform another? I don't think so, but I'm open to evidence to change my mind. Curious what you folks think.
 
Other issues to consider:

- Mechanical design/durability
- SWR bandwidth
- Affect of antenna icing
- Provision for optimizing the antenna input Z after installation, and the effort to do so

RE:
... if the three are all properly engineered for the same tower and for the same pattern, I assert that the coverage among the three will be equal ...
Click to expand...

Accurate knowledge of that would require pattern testing of each antenna by its manufacturer when mounted on a structure having the same cross-section dimensions and construction including any other "appurtenances" that will be present in the final installation. Theoretical patterns are not very useful for this.

Side-mounted FM transmit antenna elements such as the Rototiller[SUP]TM[/SUP] (ERI), opposed Vee (Jampro) etc all have different susceptibilities for the mounting environment to affect their theoretical, free-space patterns. Vertically polarized radiation is more affected than horizontally polarized radiation.

If this antenna is to be co-located with other transmit systems, it is advisable to consider how the various systems will couple to each other to produce undesired r-f intermod products that might interfere with other services -- possibly resulting in FCC action(s). This translator system (and other systems there) might require additional r-f filters in that case.
 
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