PCS Electronics US

More than any other piece of equipment the FM broadcast antenna is perhaps the least understood of all the station hardware, but more than any other piece, has the greatest potential for producing coverage gain or loss. While not intended to be a treatise on antenna theory, we hope to address some junk science myths that have been propagating throughout the industry.

1). Differences.

If we analyze differences involving quality of construction, ease of installation and maintenance, immunity to icing, and reliability, there exists variance between brands and models. Most ask what a different brand will do for their coverage, far more important factors than the minor differences between brands is the antenna height and the intervening terrain in a given fm antenna - market environment, right down to the size of the mast/pole/leg the antenna is mounted on causes effect.

Sometimes when a station changes to a new antenna, coverage changes for better or worse are noted. Actual difference (as opposed to perceived difference) is due primarily to the previously described effects produced by the tower-antenna mounting; one brand, because of slightly different mechanical geometry, happens to work out better or worse in that particular installation on that particular tower. The same antenna may produce entirely opposite results on a different tower.

All FM antenna are subject to a line-of-site path, without buildings, towers, and water tanks adding reflected images to the mix. The advertised specifications of transmission systems such as signal-to-noise and crosstalk between channels are based on this theoretical fantasy.

2). Real World.

In the real world, propagation via multiple paths represents the true nemesis of fm stereo. The most familiar result is gross distortion or even station dropout when a mobile listener waits at a stoplight. Sometimes creeping forward just a few feet clears the reception. This phenomena can be observed near the base of the fm transmitter tower where the signal strength is extreme, but the reception is terrible. The problem is caused by the mix of the direct and reflected signals present at the receiver, and is a function of local terrain and presence of reflective structures, not defects in the antenna or transmission system.

Google case studies and you will quickly discover most manufacturer's claims are based upon computer modeling, hardly what really matters. Take a real scenario where a small 100W LPFM (Low Power FM Station) ran a CP omni-directional antenna from a 60 foot HAAT tower, terrain was somewhat uneven, within a 3.5 mile radius results varied from good to very poor (FCC limitations for 100W LPFM). This station had the opportunity to re-locate their antenna on a tower that was 300 feet HAAT using the same antenna and power level their signal transposed to providing solid coverage over a 15 mile radius with acceptable reception as far out as 25 miles with static reception for another 5 miles.

A lesser-known antenna manufacturer has recently made claims of measurable results in reducing multi path through "innovative" design improvements. User reports are sometimes cited supporting these claims. It is the author's view that this is nothing more than overzealous marketing preying on people's natural wonder about the seemingly mysterious nature of antenna performance.

Reality is sometimes a bitter pill, majority of well constructed fm antenna that resonate on a particular frequency will produce similar results all things being equal. In most cases power handling and directional characteristics dictate what antenna model/type is purchased by the station.

HAAT is what counts, the higher the better, however this takes us to another factor when height is so great the engineer has to begin working out beam tilt and other factors that go beyond the scope of this essay.

When you are considering the purchase of antenna consider the following:

A). "Direction" do you need omni-directional or directional propagation.

B). "Power" the amount of RF energy will be a major decision factor, always purchase an antenna that can handle at least 25% more than your maximum input.

C). "Construction" be careful, pictures can be made to look good, check material list and specifications.

D). "Experience" nothing like it, never deal with an inexperienced person or sales company, it will cost you money.

E). "Price" by all means find your best deal but ask about service and support, cut throat retailers normally can't provide or support after sales service so be aware "you get what you pay for"