Intruder Plagues 20-Meter Service Nets

From the ARRL...


NEWINGTON, CT, Jul 27, 2001--An intruding signal that appears as a high-pitched heterodyne or squeal continues to trouble 20-meter service nets, despite efforts by the ARRL and IARU Region 2 Monitoring systems to remedy the situation. The bothersome signal--possibly a harmonic from a South American domestic broadcast transmitter--has been troubling the Maritime Mobile Service Net and Intercontinental Traffic Net on 14.300 MHz.



"We continue to work through formal and informal channels to resolve the matter," said ARRL Monitoring System Administrator Brennan Price, N4QX.



Recently, the Maritime Mobile Service Net was forced to work around the heterodyne interference to assist the US Coast Guard in the rescue of a vessel adrift in the Caribbean.



Efforts to remedy the intruder problem have been under way since May, when Virgin Islands Section Manager John Ellis, NP2B, alerted ARRL Headquarters to the squealing signal. Ellis, a controller for the two nets, provided the initial characterization necessary to identify the signal--language, programming and frequency. The AM transmissions of music and speech are in Spanish, and the signal's frequency fluctuates within a few kHz of 14.301 MHz.



Price relayed Ellis' report to IARU Region 2 Monitoring System Coordinator Martin Potter, VE3OAT, who said information and an audio clip he had received May 21 from Eric Mackie, 9Z4CP, in Trinidad and Tobago, clinched the identification as "Radio Majagual." Potter said his own monitoring verified the Radio Majagual identification. The station ID is unique to domestic AM broadcaster HJQX in Sincelejo, Colombia, which transmits on or near 1430 kHz.



Potter notes that in early 1998, HJQX was logged by short-wave listeners on a third harmonic of 4290.3 kHz. "The 10th harmonic of 1430.1 is, of course, 14,301 kHz, exactly the frequency now being observed," he said. Potter concedes, however, that he and other monitoring authorities are puzzled that such a high-order harmonic could cause such significant interference. "I still find it hard to accept a 10th harmonic," he said.



Potter has not ruled out the possibility that the signal could be a spurious or mixing product of some sort, and not necessarily a harmonic. "In fact, knowing how complicated the 'knitting patterns' of some mixing products can be, I wouldn't be surprised at anything," he said.



Potter said that, although 14,301 kHz is outside of the amateur-exclusive 14,000-14,250-kHz portion of 20 meters, the Broadcasting Service is not a legitimate user of the band 14,250-14,350 kHz.



With Potter's report in hand, Ignacio Barraquer, HK3CC, IARU liaison with Liga Colombiana de Radioaficionados (LCRA), contacted the general manager of HJQX about the suspected harmonic. While the manager expressed doubts that his station was the cause of the interference, he promised to try to take care of it.



When it became apparent that this approach hadn't worked yet, ARRL asked the FCC, through its periodic intrusion reports, to file a formal complaint through administrative channels. On July 12, the Colombian Ministry of Communications informed the FCC that the complaint had been forwarded to the appropriate department.