Given the strong debate over a voluntary FM IBOC elevated power increase, it's interesting to read about an AM IBOC-related interference dispute in California that's been going on for more than two years and new developments this month.
Midwest Television, licensee of KFMB(AM), a Class B in San Diego, has submitted a second interference complaint to the commission about Kiertron, licensee of KBRT(AM), a Class D in Avalon, Calif., and has asked the agency to suspend KBRT's authority to transmit in digital.
According to both its earlier complaint from September 2008 and the new one filed this month, KFMB says the daytime IBOC operations of KBRT have been causing "significant interference" to KFMB within its protected 0.5 mV/m contour.
Kiertron didn't dispute that it is causing interference, but responded in 2008 that it's allowed to because of a second-adjacent-channel frequency allocation waiver granted in 1962 when the station was moved, from 540 kHz to 760 kHz, after a treaty with Mexico. At that time the agency also granted KFMB a waiver "of the otherwise impermissible overlap" with KBRT, according to an FCC decision from this January.
Midwest disputed Kiertron's claim that the short-spacing between the stations justifies the interference and that the remediation procedures adopted in the IBOC order apply only to first-adjacent channel interference. The FCC this January agreed.
Kiertron said it's been trying to resolve the interference. In 2008 it asked to reduce its digital power by 2 dB. The FCC said in January this was not enough and told Kiertron to reduce its upper primary digital sideband by a total of 6 dB; it also encouraged the stations to figure out whether a 6 dB reduction solves the problem.
Now, Midwest says joint testing between the two stations showed the 6 dB reduction is not enough to solve the problem and says Kiertron has "refused to remedy" the situation; that's why Midwest has asked the FCC to tell Kiertron to suspend IBOC operation.
Midwest says it's receiving interference complaints from listeners and asked Kiertron to take part in more joint testing, but says Kiertron won't, believing further testing isn't needed.
Kiertron responded that "vociferous rhetoric" aside, Midwest has failed to demonstrate further testing is necessary while the FCC continues to review "fundamental issues" like how much protection KFMB is entitled to receive "given the significant and historical interfering contour overlap between these two stations."
"Given the unique signal relationship between KBRT and KFMB, there is no logical basis for Midwest to expect an interference-free KFMB signal at outlying distances from its tower site nor to justify that KBRT must now protect area which, by commission dictate, it has not protected for more than 40 years," wrote Kiertron in its response.
Kiertron says the earlier FCC ruling is not final and it has a pending request that the earlier decision be reconsidered; it finds Midwest's proposed remedy "drastic." Showing that it is cooperating, Kiertron says it has reduced its IBOC power "a full 75% of authorized power, or 6 dB."