In the June 10 issue of RWEE, I wrote a piece about non-directional antennas and a case in Texas where pattern distortions caused by mounting an otherwise non-directional FM antenna on the face of a large tower produced a very directional horizontal radiation pattern. That station was KFWR, licensed to Jacksboro, Texas, a community northwest of Fort Worth. This extreme pattern distortion effect was reportedly used by the station licensee to extend its coverage into Forth Worth, and in the process, it produced significant contour overlap and interference to another FM station, KCKL in Malakoff, Texas.
The licensee of KCKL complained and a long (three-year) process of back and forth ensued, culminating in a show cause order issued last March by the FCC that sought to modify the KFWR station license to specify a directional antenna, i.e. licensing the greatly distorted “non-directional” pattern as directional and forcing a reduction of transmitter power output to 45% of its nominal value so that the maximum ERP of the antenna did not exceed the C0 class maximum of 100 kW.
Both stations’ licensees filed timely responses, and on August 5, the FCC issued an order in the case. This order is available for public view.
This case has import for all FM broadcasters using non-directional antennas because all such antennas suffer from some pattern distortions as a result of mounting brackets, the supporting structure and even the interbay line, flanges and hardware. In other words, all non-directional antennas are somewhat directional, exhibiting more gain in some directions than others and with different patterns in the horizontal and vertical polarizations. We all know this. Even the FCC knows and acknowledges this.
What is disturbing, even alarming in this order is the stance the FCC is taking. In Paragraph 8 the FCC rejects the fact that the published gains of non-directional antennas are based on the RMS of the patterns. The FCC states, in effect, that the maximum lobes of each antenna cannot radiate more than the licensed ERP for the station. It says that the signal must be contained within the maximum ERP radiation envelope set forth in Section 73.211. That is a huge departure from the practice and de facto policy of the past 60+ years.
KFWR’s licensee also argued what I believe is an established fact, that hundreds or thousands of similar non-rule-compliant FM antenna installations have not been an issue for the FCC. In Paragraph 9 the FCC stated, in effect, that while that may be true, KFKR is the one we caught red handed. It’s like being stopped by the police for speeding on a stretch of roadway where everyone is speeding. They may all be speeding, but he caught you!
The ordering clause modifies the KFWR license for a TPO reduction to 9.1 kW, a reduction to 45% of its nominal 20 kW value, and it licenses the station as directional. I find it interesting that the FCC ignores the fact that the distorted pattern does not comply with §73.316(b)(1) in that it exhibits a maximum-to-minimum ratio of over 19 dB (the rule sets a 15 dB limit).
Licensees of all non-directional FM stations should take heed: we have been put on notice. Virtually every one of our stations is now in violation and the FCC now has precedent for modifying our licenses to cause a power reduction and licensing our antennas as directional. It’s unlikely that the FCC would order pattern studies for ND FM stations on a wholesale basis to establish what the directional patterns are and to what level each station must reduce its TPO to keep the maximum ERP below the licensed ERP, but the door is now wide open for interference complaints that could well result in such on a case-by-case basis.
One attorney commented to me: “My legal advice – lie low!” Good advice I would say.
I hope that KFWR’s licensee appeals this mess all the way and is successful in getting it overturned. While I do not condone what the station did and have strong feelings about the can of worms it opened up, I do support any efforts to clean up this mess. KFWR made it and now the rest of us have to live with it.
W.C. “Cris” Alexander is director of engineering at Crawford Broadcasting Co.