sidemounting of FM antenna

Whether an FM antenna that is purportedly nondirectional should be reclassified as a directional antenna, requiring that the station which uses it back down its power, was a question that the FCC addressed a few months ago in a case we wrote about here.  There, the FCC concluded that the antenna was in fact designed to radiate in certain directions far more than predicted from an omni-directional antenna, ordering the station that was using the antenna to show cause why it should not be forced to back down its power to protect stations in the direction of its maximum radiation. In a decision released yesterday (available here as a Word document, the PDF link appears to be broken) addressing the response to the Show Cause order – in a very quick action on a contested matter like this – the FCC rejected the showing offered by the licensee to defend its purported nondirectional antenna and ordered the station to reduce power. I was speaking at Georgia Association of Broadcasters annual convention this weekend, and the March decision came up in the discussion, which was of great interest to those interested in technical issues for FM broadcasters. Yesterday’s decision will certainly only fan the flames of discussion going on within the industry about this issue.

As we wrote back in March, the FCC initially found that the Texas station in question (KFWR) had effective radiated power levels almost three times those that would be predicted by its omni-directional antenna power. Looking at other evidence about the antenna, the FCC ordered the licensee to show why it should not be ordered to reduce power to bring its signal within that predicted service area – thus protecting a station that had complained of interference from the seemingly directional nature of the KFWR antenna. In response, the KFWR licensee suggested that all purportedly omni-directional antenna patterns have some degree of directionality, especially when side-mounted on a tower. The licensee argued that the FCC had never set standards for how much of such directionality should be allowed – and should not do so by singling out its application, but instead the FCC should look at this on an industry-wide basis. The licensee also offered to remount its antenna to eliminate anything that had been done to “optimize” its signal. The FCC rejected these proposals.
Continue Reading When An FM Nondirectional Antenna is Really Directional – Round 2, The FCC Does Not Back Down

In a decision of the FCC Media Bureau’s Audio Division that may be of interest to the more technically minded broadcasters, the Commission found that an FM station’s supposedly nondirectional FM antenna should be treated as directional. This decision was in response to a complaint from another broadcaster on the same channel, arguing that the broadcaster in question was exceeding its licensed effective radiated power in the direction of the complaining station (which was also the direction of Dallas, toward the more densely populated areas that it was trying to serve). The station that received the objection argued that the apparent effect on its antenna pattern was simply the result of being side-mounted on the broadcast tower that it was using, and this kind of effect was common in the industry and impossible to avoid. Yet, in reviewing the pleadings filed by the parties, the FCC found that the supposedly nondirectional station looked far too much like a directional one, and ordered the licensee to reduce power to keep its ERP (effective radiated power) in the direction where it was greatest to a value within that set out in its license. What impact will this decision have on other FM stations with sidemounted antennas?

First, it appears that the this case is one where, at least according to the FCC decision, the station had specifically designed an optimized pattern that resulted in its significantly exceeding its permitted power in the direction of the complaining station. The FCC found that, in the direction in which its maximum power was being radiated, the station had an effective ERP of 274 kw, far in excess of its licensed 100 kw ERP. The Commission noted that the direction of the highest radiation was actually not in the direction of the station’s city of license. The FCC also found that the ratio of the power in the direction of maximum radiation to the power in the direction of the minimum radiation was 19.18 dB, far exceeding the maximum 15 dB ratio permitted for directional antennas. Finding these great discrepancies in what was supposedly a nondirectional antenna led the FCC to its decision that the antenna was designed to do what it did –radiate more than permitted in the direction of the complaining station. But does this decision have potentially greater impact?
Continue Reading When is a Nondirectional FM Antenna Really Directional? The FCC Weighs In