Receiver Immunity Standards Unnecessary, Impractical for Amateur Service, ARRL Says
Responding to an FCC call for comments based in part on recommendations in a Technological Advisory Council (TAC) white paper, the ARRL this week told the Commission that establishing so-called “harm claim threshold” (HCT) standards for receivers would not work in the Amateur Service. HCTs, expressed in field strength or power flux density, would specify the level of radio interference that receivers should be expected to tolerate before a radio service could claim harmful interference. Limits would be established throughout a service’s assigned frequency range as well as within certain frequencies outside that range. The ARRL argued that there is a need for minimum, perhaps even mandatory, receiver performance standards for home electronic devices, but the Amateur Service should not be subject to receiver immunity standards.
“Any performance standards for Amateur receivers would be purely arbitrary, and would compromise the experimental purposes of the Service,” the ARRL told the Commission. “Amateurs have the technical knowledge to differentiate between interference from spurious or out-of-band emissions from nearby transmitters and that caused by receiver deficiencies.”
In the Amateur Service, the League continued, station-to-station interference issues are typically resolved cooperatively without FCC intervention and are “essentially not a problem.” The issue for radio amateurs, the League said, is “protection from spurious and out-of-band emissions from other services.”
Early last year then-FCC Chairman Julius Genachowski tasked the TAC with studying the role of receivers “in ensuring the efficient use of spectrum and to provide recommendations on avoiding obstacles posed by receiver performance to making spectrum available for new services.” In late April, the FCC released a Public Notice (ET Docket 13-101), detailing the recommendations of the TAC’s working group on receivers and spectrum in a white paper called Interference Limits Policy — The use of harm claim thresholds to improve the interference tolerance of wireless systems. A General Accountability Office report in February recommended that the FCC “consider small-scale pilot tests and other methods to collect information on the practical effects of various options for improving receiver performance.” The FCC accepted comments on both the TAC white paper and the GAO report.
The gist of the TAC white paper is that increased spectrum user density is an inevitable outcome of the growth of new wireless services, and the consequent necessity to overlay dissimilar radio services in increasingly shared spectrum requires a departure from the traditional model of placing limits on transmitters; the inability of some receivers to reject out-of-band emissions may constrain new allocations in adjacent bands, the League explained.
Reasonable HCTs for HF “Impossible to Establish”
The ARRL told the FCC that the HF environment is not conducive to fixed receiver standards and that it would be impossible to establish reasonable HCTs for HF radio equipment. “Receiver performance factors are influenced by the nature of the RF environment,” the League said, noting that relatively weak signal levels on HF affect the ability of a narrowband receiver to reject unwanted signals. In addition, the high sensitivity of such receivers makes them vulnerable to interference from in-band and external noise sources. “Filters and variable bandwidth tuning can offset these factors somewhat, but are not a complete solution,” the League said.
The FCC also should not mandate receiver immunity standards for a particular service that may compromise communication throughput, capacity or reliability or substantially increase equipment costs, “merely to allow the addition of a new service to a band that otherwise would be incompatible,” the League said in its comments. “Requiring better performance from receivers or RF-susceptible devices is a valid, reasonable, and long-overdue requirement, but the major goal of doing so should be to prevent instances of interference, not solely to allow the overlay of otherwise incompatible sharing partners in deployed spectrum to the detriment of incumbents.”
Licensed vs Unlicensed Services
The League said that inefficiencies in allocation usage owing to excessive interference susceptibility should be a criterion in determining allocations. This is especially true, the ARRL said, with respect to proposals to add a licensed service to a band in which unlicensed — and unprotected — devices are deployed. The League cited as an example its efforts to have the FCC allocate a sliver of low frequency spectrum to the Amateur Service “overlaid on unlicensed power line carrier systems of unspecified interference susceptibility.”
“Receiver inefficiencies and interference susceptibility of unlicensed and unprotected RF devices and systems should not be permitted to preclude an otherwise reasonable allocation decision in that context,” the League asserted.
Most Pressing Need
While the FCC might consider receiver immunity standards, guidelines or HCTs in some radio services, these should come about from cooperation among the FCC and industry, licensees and standards-setting organizations and consumer groups.
“The most pressing need,” the League said, “is for improved immunity of consumer electronic devices and systems. The Commission has had the authority to require this for many years, and has failed repeatedly to exercise it. The explosive growth of unlicensed devices which are RF-susceptible has stymied allocations otherwise proper and reasonable in certain frequency bands, and it has resulted in many thousands of instances of complaints against Amateur Radio operators and in some cases, civil and criminal actions being filed.”
Receiver immunity standards for the Amateur Service, the League concluded, “are neither necessary nor practical,” and the TAC recommendation to use §15.209 field strength limits as a general HCT “would effectively preclude all Amateur Radio interference complaints.”