Investigation by ARRL OOs, Researchers Leads to Resolution of 60 Meter Interference
Collaboration between ARRL Official Observers and researchers at Rutgers University has resulted in a change of operating frequency of coastal HF radars, eliminating interference to amateur stations using two frequencies in the 60 meter (5 MHz) band.
In July 2003, radio amateurs in the US received secondary privileges on 60 meters. Its strict guidelines -- no CW, operation just on five distinct channels using USB, a maximum effective radiated power of 50 W and only open to General, Advanced and Amateur Extra class licensees -- have prevented it from being popular. At first, amateurs interested in operating on 60 meters had to make modifications to the radios in use at the time. But now, more rigs are available that are designed to operate on 60 meters directly, or with a simple manipulation of menus.
Over time, radio amateurs heard various signals on the channels; users assumed these signals were those of government users and protected as such. Normally, advice to amateurs is to “use it or lose it” in regard to band usage, but on 60 meters, the watchword seemed to be “misuse” the band and lose it. So amateurs were cautious and compliant and when the band was made available to radio amateurs, users reported that everyone on the band was friendly and courteous, with at least one amateur reporting “that it was the way all the other bands used to be.”
But recently, with more users and people monitoring and using the band, amateurs began hearing more Coastal Ocean Dynamics Applications Radar (CODAR) signals on the channels. CODAR is a form of HF radar used by a number of institutions to research and study ocean currents and waves. Amateurs frequently reported CODAR sounds as that “repetitive loud swishing sound” on the band.
“After comparing reception reports of these signals that we had been hearing on the East Coast and reports he had received from amateurs on the West Coast, ARRL Orange Section Official Observer Coordinator Dan Welch W6DFW, followed up on them and began doing some research,” explained ARRL Field and Regulatory Correspondent Chuck Skolaut, K0BOG. “We alerted Official Observers -- especially along the coast -- to monitor and forward reports.”
Welch enlisted the assistance of a number of these Official Observers and other stations to monitor the frequencies after he had received more observations. Through good cooperation with the FCC, he was able to ascertain that CODAR was being used by Rutgers University on channels 3 and 4 in the 60 meter amateur band.
According to Skolaut, much of the follow-up included good cooperation from the CODAR group at Rutgers, including Josh Kohut and Ethan Handel. Rutgers is part of a regional partnership working on ocean observing. Kohut told the ARRL that information they gather is used by the Coast Guard, fisheries, off shore energy facilities, storm forecasters and pollution studies. He explained that the transmitters are capable of 40 W and provide information from up to 100 miles.
Welch and Handel coordinated testing, and amateurs were contacted to help monitor the frequencies as Handel shut down the various transmitters in their network to determine which ones amateurs were hearing. “They conducted two tests a week apart and it was definitely determined that the pulses being heard on the two channels were being transmitted from one or more of their sites,” Skolaut said. “It is interesting to note that the West Coast stations were able to hear the East Coast CODAR much of the time, depending on propagation. After consulting with Welch, the Rutgers team was able to move their transmitter frequencies outside of the amateur band to 4.9 MHz to continue their valuable ocean research. Both Handel and Kohut said that they were glad we were able to resolve this issue in a mutually beneficial way. Now once again, 60 meters is quiet with regard to CODAR signals.”
Skolaut encourages amateurs to check out the band and sample what those frequencies have to offer, taking into regard the various restrictions for its use: “While conducting the monitoring checks, we noted a number of relaxed QSOs taking place on the other 60 meter frequencies, including a number of UK stations coming in quite nicely here on the East Coast on channel 5. This is a common frequency available to amateurs in the United States and the UK. Sixty meters is a band that fills the gap between 40 and 75 meters on phone quite nicely at times. It may truly be the ‘hidden treasure’ of the amateur bands.”
For more information on 60 meters, please check out the 60 Meters FAQ page on the ARRL website.