ARRL Seeks to Protect 2304 MHz Operation


In May, as a partial implementation of its National Broadband Plan, the FCC adopted amendments to its rules for Wireless Communications Services in the 2.3 GHz band to permit mobile broadband services, in addition to fixed services, in the bands 2305-2317.5 and 2347.5-2360 MHz. The Report and Order (R&O) in WT Docket No 07-293 was published in the Federal Register on August 2, 2010, triggering a 30 day window for petitions for reconsideration. On September 1 the ARRL filed a Petition for Clarification or Partial Reconsideration, asking the FCC to clarify, or partially reconsider a single aspect of its Report and Order.

Specifically, the ARRL requested that the Commission affirm:

  • That Section 2.102(f) of the Commissions rules applies to Wireless Communications Service (WCS) fixed and mobile operations, so that harmful interference that is caused to Amateur Radio Service operations in the 2300-2305 MHz band is to be remedied by WCS licensees.
  • That the current out-of-band emission (OOBE) limits for WCS devices set forth at Section 27.53(a)(3) of the Commissions rules continue to apply to mobile, portable and fixed facilities across the entirety of the 2300-2305 MHz band following the rule changes implemented in this Order.

The FCC claims that its rules changes do not risk harmful interference to neighboring operations, specifically claiming to protect adjacent satellite radio, aeronautical mobile telemetry and deep space network operations. The ARRLs concern is that the Amateur Radio Service is noticeably absent from the listed group of interference-protected services affected by these rule changes.

The Amateur Radio Service has a secondary allocation at 2300-2310 MHz. The fixed and mobile services are primary at 2305-2310 MHz, but at 2300-2305 MHz the amateur allocation is not shared domestically with any other service. The band is regularly and substantially utilized by radio amateurs for narrowband (i.e. 3 kilohertz bandwidth emissions or less) long-distance propagation communications using exceptionally weak received signal levels, most especially around 2304 MHz, the ARRL pointed out in its comments. This type of operation has proven over time to be completely compatible with deep-space research and other operations below 2300 MHz, and the ambient noise levels in the 2300-2305 MHz band are historically very low, making the band attractive for amateur weak-signal communications, the principal amateur use.

The ARRL noted, however, that even though high power WCS fixed operations above 2305 MHz have not proven to be a significant noise source in the past -- perhaps due to the relative absence of such facilities -- it must be assumed that mobile broadband devices will proliferate at and above 2305 MHz following the R&O and that they will be operated in close geographic proximity to amateur stations operating in the 2300-2305 MHz band.

The Commission noted at Footnote 405 of the R&O that out-of-band emissions (OOBE) from WCS, when expanded to permit mobile broadband and portable devices at up to 250 mW EIRP, could be expected to have an effect on amateur operations in that band: We note that some amateur stations operating around 2304 MHz may experience an increased antenna noise temperature caused by the implementation of mobile WCS operations, and will have to tolerate this change in the RF environment. Due to the technical flexibility allowed to amateur stations in Part 97 of our rules, however, we believe that operators of these stations may be able to offset or mitigate the effects of this change by relocating or redirecting their antennas, or by making other permitted technical adjustments.

Calling this a cavalier dismissal, the ARRL maintains that it represents the latest in a series of instances in the past few years in which the Commission has made unwarranted and completely incorrect assumptions about the ability of amateur stations to avoid preclusive interference from an incompatible spectrum use by reorienting or relocating antennas. These assumptions are made without any factual basis at all, in order to justify an allocation decision the Commission desires to make.

The ARRL pointed out that it is, in most cases, impossible to relocate an antenna array -- especially for the 2300-2305 MHz band -- as those are typically large, fixed antenna arrays. Also, redirecting a directional antenna is possible in some instances, assuming that the station from which an amateur station desires to receive signals is not located in or near an azimuth that includes a mobile broadband device, in which case the amateur communication is precluded. In any case, however, the operation of mobile broadband devices can be anticipated to be ubiquitous, making the redirecting of amateur antennas an exercise in futility, the ARRL said.

In any case, Section 2.102(f) of the Commissions Rules states rather clearly that (t)he stations of a service shall use frequencies so separated from the limits of a band allocated to that service as not to cause harmful interference to allocated services in immediately adjoining frequency bands. Given this, it is clearly the obligation of the WCS mobile facilities providers to avoid interference to Amateur stations operating in the band 2300-2305 MHz.

Citing calculations that show the increase in noise from a mobile device 30 meters away could be as much as 51 dB, the ARRL said “…it is critical to establish a firm, workable OOBE limit for these facilities at the outset, as the only means of protecting regular, ongoing Amateur Radio communications in this band. It is necessary, therefore, for the Commission to clarify now, preferably by revising the adopted rule sections 27.53(a)(1)(ii), 27.53(a)(2)(ii), 27.53(a)(3)(ii) and 27.53(a)(4)(ii), that the cited rule sections do in fact require that OOBEs for mobile stations must be attenuated over a 1 MHz bandwidth below the transmitter power (P) by a factor not less than 43 + 10 log (P) dB on all frequencies between 2300 and 2305 MHz. It is also important to place the burden of harmful interference resolution where it properly belongs, and where Section 2.102(f) places it: on the WCS licensee and not on the victim Amateur Radio Service licensee operating in the 2300-2305 MHz band.