The NPRM seeks input on a number of questions that rulemakers are still pondering when it comes to implementation of the new bands. Stakeholders are requested to submit comments on a number of issues addressed in the document and have 60 days to do so once the document has been published in the Federal Register which is updated daily.
Following submission of comments, a number of options still remain open for FCC rulemakers and I rather suspect, from the vast scope of the NPRM's inquiry, that the process could drag on for some length of time yet. Take solace in the fact that the NPRM is indeed a necessary step in the right direction and shows that the proposals are moving forward, finally!
The major focus of the NPRM appears to be centered around determining appropriate levels of power and the viability of amateurs coexisting on the frequencies shared with Power Line Carrier (PLC) systems. Indeed the major stumbling block, at least as far as 2200m is concerned, has always been the strong objection from power authorities that amateur signals will interfere with their control signals. PLC interference as well as possible interference to the Maritime Mobile Service (MMS) is also cited as a concern for the 630m proposal. One might argue that lumping these two bands together in a single NPRM is the best way to go while others might say that chance of success would be much better by treating them separately ... time will eventually tell.
Getting into more detail, the NPRM commentary specifically affecting our LF/MF interests, address the following critical points (and present stumbling blocks):
Service Rules for the 135.7-137.8 kHz and 472-479 kHz bands. We are proposing service rules for the amateur service in the 135.7-137.8 kHz and 472-479 kHz bands with the principal goal of enabling sharing of this spectrum among licensed amateur stations and unlicensed PLC systems.
As the demand for radio spectrum has continued to increase, we have sought to make more efficient use of spectrum by providing for sharing of frequency bands for multiple purposes.While we recognize the importance of PLC systems to the functioning of the electric power grid, we also believe that there are benefits to providing amateurs access to these bands, including providing amateurs with new opportunities for experimentation. Moreover PLC systems and the expected amateur use of these bands have characteristics which make coexistence possible. PLC systems are limited to use on transmissions lines and, consequently, are not present in most residential neighborhoods where amateur licensees live.
The amateur service is expected to use the band mainly for experimental purposes and not for routine and widespread communications activities common in other bands. These attributes give us confidence that,
along with appropriate technical rules, amateur stations can harmoniously operate on the same frequency bands as PLC systems.
The cornerstone of the technical rules we are proposing is physical separation between amateur stations and the transmission lines upon which PLC systems may be present. We propose that amateur stations be permitted to operate in these bands when separated from transmission lines by a specified distance. Such a separation, in conjunction with limits on the amateur stations’ transmitted EIRP and antenna heights, will enable PLC systems and amateur stations to coexist in these bands. In addition, we propose to limit amateur stations to operations at fixed locations only to ensure that this separation distance can be maintained reliably. We seek comment on this overall framework.
In order to develop the necessary and appropriate service rules to meet our goal of providing for the coexistence of amateur services and PLC systems in these bands, we seek detailed comment on the technical characteristics of both the PLC systems and the amateur stations. This information will allow us to set an appropriate separation distance. Although the Commission in the WRC-07 NPRM inquired into the technical rules and methods that would assure coexistence, commenters provided little in the way of concrete information. ARRL submitted a technical analysis based on an NTIA technical report supporting an assertion that PLC systems in the 135.7-137.8 KHz band will be sufficiently protected from amateur stations transmitting at an EIRP of 1 W with a separation distance of 1 km from the transmission lines carrying the PLC signals. However, this NTIA technical report is from 1985 and therefore may not account for any subsequent developments.
To assist us in determining the optimal separation distance, we invite commenters to submit information on the technical characteristics of PLC systems that are currently being operated by utilities or likely to be deployed in the future. How tolerant are these PLC systems of signals received from other stations transmitting in the same band? What electric field strength at the location of a transmission line will cause a PLC system operating on that line to malfunction? What types of malfunctions would the electric power grid experience from electrical interference? How many PLC systems are currently operating in the 2200 and 630 Meter bands? Can these existing PLC systems be modified and could new PLC systems be designed to operate in other portions of the 9-490 kHz band, thus avoiding co-channel operation with amateur services? At what power do these PLC systems operate and how long are the transmission lines over which they send signals? At what voltage level do the transmission lines upon which these PLC systems are deployed operate and how does the PLC systems’ tolerance of other signals depend on the voltage level? What electric field strengths are produced in the vicinity of transmission lines by the PLC signals travelling over the transmission lines?
We likewise invite information on the technical characteristics of amateur stations that are likely to be deployed or have operated under experimental licenses in these two bands. What electric field strength generated by PLC systems operating on transmission lines would impede the operation of
amateur stations? A study conducted on a PLC system operating at 1 W at 152 kHz found that the PLC system generated an electric field strengths of 20 dbμV/m at 1 km. Would a signal with this field strength interfere with the operation of amateur stations? Given that high-voltage transmission lines generate a significant level of noise at this frequency range, how close to high-voltage transmission lines can amateur stations realistically operate? In recent years amateur stations have operated in these bands
under experimental licenses with most licenses permitting powers of between 1 to 20 watts ERP. How close did these amateur stations operate to transmission lines? Did any of these amateur stations receive
signals from PLC systems operating on transmission lines? Do the experiences of amateur stations and utilities in other countries and along the United States border with Canada yield any useful information?
If we were to adopt our proposal to permit amateur operations only when separated by a specified distance from transmission lines, when a new transmission line is built close by an amateur station, the station either would have to relocate farther away from the transmission line or cease
operating. How should our rules address the potential for new transmission lines to be constructed closer than the specified distance to pre-existing amateur stations? We do not want to inhibit the ability of either PLC systems or amateur services to grow and expand without imposing unnecessary burdens on either. Is it possible for utilities to refrain from geographically expanding their PLC operations within the relatively small portion of the 9-490 kHz band that we are making available for amateur operations, and is this something utilities would do on their own accord, given the Part 15 status of PLC systems? Should our rules explicitly prohibit utilities from deploying new PLC systems in these bands?
....to be cont'd