FCC seeks comment on unlicensed operation in three bands.
The FCC’s Further Notice of Proposed Rulemaking on outdoor and in-tank radars in the 5.925-7.250, 24.05-29, and 75-85 GHz bands has now appeared in the Federal Register. As regular readers realize, that establishes the official deadlines for anyone wishing to chip in their two cents’ worth. Comments are due on May 30, 2012 and reply comments on June 29.
Level probing radars at 6, 26, and 80 GHz would have adequate power for a wide variety of industrial applications.
The FCC has proposed new rules for “level probing radars” (LPRs) in three bands: 5.925-7.250 GHz, 24.05-29 GHz, and 75-85 GHz. LPRs are downward-aiming radars used to determine levels of materials at industrial installations. Some are mounted inside those enormous tanks that dot the industrial landscape, to tell the operators how much liquid is inside. Other LPRs are used outdoors – at quarries, for example, to measure piles of gravel, or at nuclear power plants, to monitor the water level in the ponds used to store highly radioactive fuel rods. There are thousands of potential applications. The new rules would apply equally to in-tank and outdoor radars.
The FCC is easing its way into this area very gradually. More than two years ago, it proposed rules to allow in-tank radars in the 77-81 GHz band, and granted a waiver pending the rulemaking. Without having reached a decision on the original questions, the present Further Notice of Proposed Rulemaking expands the proceeding to add outdoor LPRs and more frequency ranges. Up in the nosebleed part of the spectrum, the FCC had earlier proposed radars for airport use at 78-81 GHz, to detect debris on the runways, and a relaxation of the vehicle radar rules at 76-77 GHz to allow non-vehicle applications and higher power.
An LPR typically transmits a train of very short pulses, with relatively long separations in between. For historical reasons, the FCC’s technical rules are more hospitable to continuous transmissions, such as those used to carry voice and data signals. The same rules, when applied to a pulsed transmission, effectively require operation at greatly reduced power. That lower power is sometimes adequate for measurement of highly reflective surfaces, but otherwise has largely prevented the successful operation of LPRs.
The newly proposed rules, being specifically geared to LPRs, should allow the downward-aiming transmitter to provide adequate power for a wide variety of applications. To protect other spectrum users from interference, the FCC has proposed much more stringent limits on radio-frequency emissions from the sides of the device and upward. Those stray emissions can be due either to properties of the antenna or to reflections from the material being measured. In the 24.05-29 and 75-85 GHz bands, they are limited to the same very low levels that are permitted for an iPad or a digital toy: 70 billionths of a watt. In the 5.925-7.250 GHz band they must be lower still, at about 3 billionths of a watt.
Comments and reply comments will be due 30 and 60 days, respectively, after publication in the Federal Register. We will let you know when that happens.
Not as momentous as the Julian-Gregorian shift, but changes you might want to note nonetheless
Back in January we reported on a proposal to allow unlicensed operation in the 77-81 GHz band for “tank radar” use. The Commission’s Notice of Proposed Rule Making has now been published in the Federal Register, which in turn has established the deadlines for comments and reply comments. Comments are due by June 2, 2010 reply comments by July 2, 2010.
And in February, we called readers’ attention to the First Report and Order and Notice of Proposed Rule Making (FRO/NPRM) in the rural radio proceeding. There the Commission adopted a Section 307(b)-based “tribal priority” for new AM and FM allotments, and separately invited comments on possible further tweaks to that priority (e.g., whether and how to apply that priority to Native American Tribes who do not possess tribal lands). The FRO/NPRM has also been published in the Federal Register. That publication sets the comment deadlines for the NPRM section of item (comments are due by May 3, 2010, reply comments by June 2, 2010). Additionally, the publication makes the “tribal priority” and other changes adopted in the R&O portion effective as of April 5, 2010. (Check out our earlier post on this for a summary of the various changes.)
While the “tribal priority” is not likely to affect the lay of the AM and noncommercial FM land for the time being – since new allotment proposals there require the opening of a “filing window” by the Commission, and no such windows are currently on the horizon, as far as we can see – it could affect commercial FM drop-in proposals early on. However, in view of the lag time between (a) the inclusion of new commercial channels in the Table of Allotments and (b) the opening of a window opportunity to file for those channels, increased service to Native American tribal lands as a result of the “tribal priority” is still probably a ways away.
FCC moves to allow 77-81 GHz radars inside storage tanks.
Driving through an industrial area, looking at the huge storage tanks that dot the landscape, don’t you wonder how the users of the tanks know how much stuff is inside? Neither did we, until recently. If we thought about it at all, we imagined some kind of giant float, like the thing in the back of the toilet, except much bigger. But that couldn’t be very reliable, considering it’s not all that reliable in the toilet, either.
Many of the big tanks have a better system. A radar device sits up on the ceiling, looking down. It transmits short pulses, measures the time they take to come back, and computes the distance to the surface inside. Using radar avoids problems of corrosion, contamination, and the endless repairs needed for moving parts in the vicinity of liquids.
Other equipment inside the tank – valves, agitators, filling pipes, and so on – also reflects radar signals, as do the tank walls themselves, and that can lead to errors. One solution is a radar beam narrow enough to miss the other structures and strike only the liquid directly below. But then those pesky laws of physics intervene. The most feasible way to produce a narrow beam, using a reasonably sized antenna, requires transmitting at high frequencies.
The manufacturers of tank radars favor the 77-81 GHz band. This is well up in the nosebleed portion of the spectrum, among the very highest frequencies the FCC has ever authorized. From an engineering standpoint, it is an excellent band for the purpose. Not only do signals at these frequencies form tight beams, but they are absorbed by metal and concrete tank walls, and so do not escape the tank to threaten interference to receivers outside.
From a legal standpoint, though, the band has a problem. Everyone agrees that tank radars should be authorized on an unlicensed basis, like Wi-Fi and cordless phones. But 77-81 GHz falls within a list of “restricted frequencies” that are closed to unlicensed transmitters. Most frequencies on the list accommodate highly sensitive services such as GPS, search-and-rescue, and satellite downlinks. But when the FCC drew up the list in the 1980s, it deemed everything above 38.6 GHz to be restricted. There was little activity up there in those days, and the FCC reasoned it could always de-list frequencies later, if the need were to arise. And in fact the Commission has since done so for several individual bands, for certain purposes. But otherwise the blanket prohibition on unlicensed operation above 38.6 GHz remains in force.
As a result, despite a near-unanimous view that unlicensed 77-81 GHz tank radars will not cause interference, the FCC is legally barred from allowing them under the present rules. The FCC has accordingly launched a proceeding to change its rules to permit these radars to operate. It also issued a temporary waiver allowing use of these radars, under certain conditions, while the rulemaking is pending.
The only opposition so far comes from a group of radio astronomers, who have primary rights at 77-81 GHz. Fearing interference to their telescopes, they asked for a mandatory separation of two kilometers between tank radar installations and the astronomers’ sites. The FCC indicated its intention to deny the request, on the ground that any slight leakage from inside the tanks would be too weak to cause interference.
The rule change is obviously the right thing to do. But it points up a broader problem: the need to abolish the blanket prohibition on unlicensed operation above 38.6 GHz. Rather than continue to exempt various bands piecemeal, the FCC should decide once and for all which bands really do need protection and drop the rest from the restricted list. Why does this matter? The initial request on 77-81 GHz tank radars reached the FCC in November, 2006. (Two more followed in April and July, 2007.) Three years is a long time to wait for proposed rules and a temporary waiver, especially for a technology widely considered to be non-interfering.
More is at stake here than just tank radars, important as those are. As the lower part of the spectrum fills up, and as prices drop for equipment that uses the upper reaches, demands on the over-38.6 GHz segment will rise. Amending the list of restricted frequencies now will help to avoid unnecessarily long delays in the future.
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