WASHINGTON, D.C.—The FCC Media Bureau has announced  that effective August 1, 2024 the Commission’s TVStudy software will incorporate the most recent U.S. Census Bureau decennial Census block and population data (2020 Census Data). 

The Commission’s TVStudy software is used to perform coverage and interference analysis of television stations in connection with the preparation and processing of full power rulemaking petitions to allot channels to the Table of TV Allotments and in applications prepared by  television licensees and permittees when they seek to modify their facilities, the agency said. 

The move means that all television broadcast applications filed on or after August 1, 2024, will be required to utilize 2020 Census Data for purposes of conducting interference analyses, the Media Bureau reported. Those who don’t use the 2020 data will be required to amend their applications and may see their applications dismissed “as defective.”   

The Media Bureau also noted that in a separate Public Notice, The Office of Engineering and Technology announced the release of updated TVStudy software (Version 2.3.0).

The TVStudy Version 2.3.0 software, the TVStudy 2.3.0 Installation and Upgrade Guide, and the template XML file are all available on the TVStudy website at http://www.fcc.gov/oet/tvstudy.

The agency also stressed that a full list of changes from TVStudy Version 2.2.5 is included in the “Differences Between 2.3.0 and 2.2.5” section of the Change Log in the TVStudy 2.3.0 Installation and Upgrade Guide.

The agency said that further information regarding this Public Notice can be obtained by contacting Kevin Harding at (202) 418-7077 or Kevin.Harding@fcc.gov; or Mark Colombo at (202) 418-7611 or Mark.Colombo@fcc.gov. 

WASHINGTON—Several groups representing users of private land mobile radio (PLMR) systems are urging the FCC to enforce rules that prevent interference from TV stations that recently moved their transmission facilities during the three year-channel repack that recently concluded.

In a letter to the FCC, the Land Mobile Communications Council asked the commission to take action against numerous instances of radio interference from stations that moved to new channels as a result of the 2017 spectrum auctions that transferred portions of broadcasters’ 600 MHz spectrum mostly to wireless carriers seeking to upgrade to 5G. 

These PLMR facilities have been in operation for decades and provide essential fleet dispatch communications for a broad range of business and governmental users, including hospitals, school buses, roadside assistance, highway maintenance, refining, petrochemical production, high voltage electrical repair and firefighting.

Interference issues between the two systems is nothing new. In the mid-2000s, the FCC had to intervene when reports of garage door openers were also interfering with PLMR systems. Those situations and others like that, the LMCC said, were temporary and usually fixed in a reasonable time period and didn’t have the same impact. 

“This interference is so strong that it takes the PLMR systems off the air and is occurring for many hours several days a week or even multiple consecutive days,” the LMCC told the FCC.

LMCC says the situation represents a threat to public safety and to the loss of business. 

“This interference has rendered affected PLMR facilities entirely unusable in certain markets, resulting in hundreds of thousands of dollars of lost revenue as customers of commercial systems are forced to search for alternative communication options and incurred expenses as licensees have sought remedial action by the broadcasters and/or acquired other spectrum to which their operations could be moved,” the LMCC said. “The interference with what had been reliable communications endangers the safety of employees, disrupts operations at affected facilities and poses a major threat to public safety in certain instances. The urgency of the problems demand FCC action to enforce those regulations and policies as promptly as possible and to avoid the creation of similar problems in the future.”

LMCC said it assumed that the stations causing the interference are ones that recently moved due to the repack and as such, are obligated to resolve the interference issue.

PLUS: Repack Crosses the Finish Line

“In such cases, the FCC has relied on its long-standing ‘newcomer’ policy pursuant to which new licensees are responsible for resolving interference caused by their operations even if all parties are operating in accordance with the rules and the terms of their authorizations,” it told the commission. “In this instance, it is vital that the newcomer DTV stations assume this obligation because there are no anti-interference solutions available to the PLMR licensees.”

Citing rules that require TV stations to identify potential interference before construction, the LMCC said the issue can be easily resolved if the FCC enforces those rules. 

“A number of new permittees have been diligent both in identifying potentially affected PLMR systems and, more importantly, in implementing the necessary filtering to avoid causing interference,” LMCC said. “Their success makes clear that those facilities can co-exist when appropriate interference mitigation measures are taken by the DTV station.”

The Enterprise Wireless Association echoed LMCC’s concerns and calls for action. 

“Some EWA members are so frustrated that they wonder if the reaction of a few TV stations might be ‘There is nothing we can do; the environment is the root cause; we didn’t want to move in the first place; or, maybe the PLMR incumbents will go away in time and leave us alone,’” said EWA President Mark Crosby. “Of course, these are unacceptable responses as the PLMR industry is as vital to the well-being of this country as are broadcasters, even if not as well known. The LMCC seeks only a fair hearing and the FCC’s active support towards a resolution. That should not be wishful thinking. EWA remains optimistic.”

The LMCC’s report citing specific interference cases is available here. 

WASHINGTON—The NAB is preaching caution as the FCC looks to possibly expand unlicensed operations in the 6 GHz band, arguing that no such decision should be made until there is a clearer picture of the impact of the already approved unlicensed use in the spectrum.

In April, the FCC unanimously approved opening the entire 1,200 MHz of the 6 GHz band for unlicensed Wi-Fi operation as part of the commission’s strategy to develop 5G.

Broadcasters at the time were worried about the potential interference that could have on the services they have operating in the 6 GHz band, like fixed links delivering content from broadcast studios to transmitter sites and mobile transmissions from ENG trucks. The NAB noted how these services have been particularly critical during the current pandemic.

Now, a Further Notice of Proposed Rulemaking deals with increasing the power levels permitted for low-power indoor operations from the current 5 dB/MHz to 8 dB/MHz.

“Time will tell if the commission was correct in its determination that interference is unlikely to occur, despite broadcasters’ substantiated concerns that the minimal protections the Report and Order establishes will prove insufficient,” the NAB said in its comments. “But it is plainly premature at this time to increase the power levels permitted for LPI operations by an additional 3 dB when there has been no opportunity to test the commission’s assumptions in the marketplace.”

In addition, the NAB has raised concerns about the FNPRM’s proposal to permit very low power operations across the 6 GHz band, indoors and outdoors, with no automatic frequency coordination. NAB says that none of the mitigation techniques or factors in the FNPRM are likely to ensure protection for BAS operations.

“Accordingly, we urge the commission not to take further action to authorize higher power LPI operations or VLP operations until more is known about the ability of unlicensed and licensed users to coexist in the band,” NAB concluded.

The NAB wasn’t the only group to submit a comment to the FCC recently, however. In response to a petition from the Edison Electric Institute for a preliminary stay on the use of LPIs in the 6 GHz band, TVT’s sister publication Multichannel News has reported that computer companies like Facebook, Apple, Google and Microsoft call on the FCC to reject the petition.

NAB’s full comments are available online. 

WASHINGTON—The NAB has done its homework on potential interference to electronic newsgathering services utilizing the 6 GHz spectrum band from unlicensed Radio Local Area Network Wi-Fi-type devices, and has provided that data to the FCC to advocate against uncoordinated unlicensed use.

In October 2018, the FCC proposed opening up the 1,200 MHz of the 6 GHz midband spectrum for unlicensed use. Broadcasters traditionally use the 6 GHz band for auxiliary operations, like sporting events, breaking news and special events.

The FCC has not officially voted on it, allowing for interested parties to provide comments. That is what the NAB did in a filing it sent to the commission on Dec. 5.

Writing that those proposing that the deployment of RLAN in the spectrum would have little to no impact defies “past experience and common sense,” the NAB provided the commission a report conducted by an engineering firm, Alion, that looked at the likelihood and extent of interference to ENG systems using three common ENG deployment use cases: indoor camera to indoor receiver; outdoor camera to news truck; and outdoor news truck to central receive site.

For indoor ENG operations, Alion found that interference could be expected 0.9% in best case scenarios and 95.3% in worst case scenarios. Outdoor ENG operations saw potential interference 0.4% to 66.9%. Finally, transmitting to a central receiver site, Alion reported that interference was predicted every single time.

“ENG systems are a critical component to public warning, newsgathering and content generation,” the NAB wrote, also pointing out that broadcasters have already loss access to channels at 2.5 GHz due in part to interference from 2.4 GHz Wi-Fi systems. “Based on that experience, we are certain that uncoordinated RLANs will cause interference to 6 GHz ENG systems.

The NAB does say that there is an opportunity to provide additional spectrum for Wi-Fi use in 6 GHz—Microsoft, broadband operators and wireless carriers are also seeking to utilize some, or in some cases all, of the 6 GHz spectrum—but that “it must not risk eliminating the non-common carrier mobile uses in the spectrum by allowing unrestricted, uncoordinated use, even if limited to indoor locations.”

Read the full ex parte filing from NAB here.

ALEXANDRIA, VA.—The U.S. incentive auctioning of television broadcast spectrum has been shrouded in uncertainty ever since it got underway, with broadcasters and others expressing a growing list of concerns. However, there is one item that hasn’t received a lot of attention—the potential of RF interference to both repacked TV operators and wireless broadband operations from Canadian and Mexican television stations.

Can U.S. DTV and wireless broadband co-exist with transborder broadcasters in a repacked world? PHOTO CREDIT: Peter Starke, American Tower Corp.

Although the FCC developed software for modeling repacking scenarios on a market-by-market basis (including potential for both TV station interference and impairment to blocks of 600 MHz spectrum cleared for auction), and contends that the potential for interference is very low in border markets, there are skeptics.

“It would be nice if Canada and Mexico would fall in line with the repack in a timely way,” said Chares W. (Charlie) Rhodes, long-time TV Technology columnist and a recognized industry expert in interference issues. “However, the last thing that either country would stand is for the United States to dictate TV coverage in their countries, especially if there is no ‘quid pro quo,’ and right now there isn’t any. Memorandums of understanding between countries don’t mention compensation, and it’s not the usual practice in situations like this to give without taking.

“This is one of the items that I think may be unresolved in this auction,” Rhodes continued. “The FCC is being very close-mouthed about it and the Department of State has said nothing. There are a whole bunch of issues, any one of which could delay the availability of spectrum for stations along the border to shift frequencies.”

NO INCENTIVE
Rhodes’ concerns were echoed by Bill Meintel, senior partner at the RF consulting firm, Meintel, Sgrignoli, and Wallace.

“There’s no incentive for the Mexican and Canadian stations to move unless their governments force them to, but I doubt if this would happen,” said Meintel. “On the other hand, it could come down to the wireless carriers putting up money for such moves.”

Meintel said that he had television clients in border areas that could be impacted, but it was too soon to know if they might face interference problems.

Bill Meintel

“You’re not going to know what the situation will be until you know what channel they’re going to land on,” he said. “My understanding is that the FCC is going to use the scheme in the 2014 Report and Order to determine if they can use particular channels. They’re going to look at a station’s existing service in 2012 as the baseline. There has to be a reasonable effort to maintain this coverage. They will look at the points where service exists now that’s not impacted and then look at how much interference this new entry will cause, and they’ll allow up to one-half of a percent new interference. I think there is potential for additional interference, because each evaluation is one-on-one.

“My concern is that if they start having problems trying to make this work in getting the amount of spectrum they want, they may renege on this half-percent interference,” Meintel continued. “They could claim that it’s in the public interest to allow more interference so there can be more spectrum for wireless broadband. We’ll see how this all goes, but I’m skeptical.”

NAB SEES POSSIBLE CHALLENGES
Dennis Wharton, executive vice president of communications for the National Association of Broadcasters, was asked to share his thoughts on possible cross-border interference issues.

“Throughout all of the [spectrum auction] discussions, all stakeholders have identified border areas as areas of complexity,” said Wharton. “There is no mechanism in place for funding moves in [Canada and Mexico] and no timeline. We can’t predict when this will happen. We really have no position on this, other than it could potentially pose challenges, but it is up to broadcasters in those countries to move.”

Wharton praised the FCC for their work in obtaining the agreements for cooperation that are now in place and noted that the NAB had worked with the FCC in setting up methodologies for predicting interference cases and reiterated the commission’s pledge to U.S. broadcasters.

“The FCC adopted a zero interference policy for broadcasters; they can’t be interfered with.”

WIRELESS BROADBAND INTERESTS FACE PROBLEMS
It’s not just U.S. broadcasters who harbor concerns; telcos could face some thorny issues too.

“The broadband people have told the FCC that there are problems, but the FCC said ‘no, our computer modeling says otherwise,’” said Rhodes, noting that he’s measured interference thresholds to wireless broadband services from television stations and it’s far from zero, and that such warnings have been published in ITU proceedings, but ignored by the FCC.

Rhodes observed that wireless networks would likely have coverage holes if Canadian and Mexican broadcasters don’t follow suit with those in the U.S. in repacking.

“Who is going to want a mobile phone that doesn’t play anywhere and anytime?” Rhodes mused. “This doesn’t happen now, but the situation will be quite different when interference sources are megawatt ERP TV transmitters. However, the FCC continues to push forward with a ‘whatever happens, happens’ attitude.

“I believe that the broadband interests are going to be very hesitant about committing money for spectrum if they don’t know when they’re going to get to use it,” Rhodes continued. “The FCC needs to resolve this before the auction. Telco managements will need to know when the spectrum will be available.”

In accordance with spectrum auction confidentiality, wireless broadband service providers are not allowed to comment publically about the auction; however, some are voicing concerns about unresolved interference issues. One member of the wireless industry, speaking under conditions of anonymity, stated that while there were agreements in place between respective governments, “the challenge is that there is currently no timeline, nor any reimbursement funds for TV station moves in Canada and Mexico,” and noting additionally that Mexico’s refusal to adopt the U.S. band plan will further complicate matters.

“If Canada and Mexico do not timely move, border markets will remain impaired, so we anticipate that there will be continuing challenges at the border,” the source said.

IS THERE A WORKAROUND?
Meintel related that an interference “solution of sorts” was achieved following a wireless carrier’s purchase of TV Channel 52 spectrum and the recognition of potential interference issues with Channel 51 broadcasters.

“The concern was not so much that they would be interfering with TV stations, but that TV stations would be interfering with them,” said Meintel. “Technically, they had to protect the television station’s service contour, which meant they couldn’t operate inside it and the market they wanted to cover was the same as the TV station’s. The only way they could operate was to get stations to accept the interference potential. This happened in a number of situations. The stations figured that they were reaching enough people on cable and were OK with the interference potential if the wireless broadband company was willing to write a check.

“On the other hand, there were stations who not only said no, but ‘hell no!’”

WASHINGTON—There will more interference than FCC anticipates in the duplex gap. That’s the upshot of a filing on the Federal Communications Commission’s Incentive Auction docket made by Mark Aitken, vice president of Advanced Technology for Sinclair Broadcast Group.

“Interference prevention is the raison d’être of the FCC,” he wrote. “The laws of physics have not changed and repacking broadcasters in bands reserved for mobile wireless broadband highlights the commission’s challenge.”

The commission is proposing to place orphaned TV stations in the duplex gap—the band of spectrum between wireless up- and downlink frequency blocks. Orphaned TV stations will be those not sold in the auction, and that the FCC can’t find a channel for in the TV band after the auction. The FCC is proposing to put these TV stations into the duplex gap, something both broadcasters and wireless providers oppose. The FCC, however, says it needs the flexibility of assigning stations to the duplex gap in order to reach its spectrum-clearing goals.

The impact of doing so remains disputed.

Aitken submitted an article by TV Technology contributor Charles Rhodes, “Assessing Post-Repack Channel Options.” Rhodes was chief scientist at the Advanced Television Test Center, a non-partisan, independent testing facility set up to develop digital TV technology. He is also a recipient of the David Sarnoff Medal and holds several patents. He now conducts signal-interference tests in his own facility and reports the results in TV Technology.

“Using the commission’s recently adopted ISIX model, Mr. Rhodes cautions that harmful interference will indeed occur and be far greater with the aggregation of ‘super blocks’—10 MHz wide assignments—by wireless carriers,” Aitken writes. “ISIX interference can arise from signals offset in frequency by more than 6 MHz. In fact, Mr. Rhodes notes that two Super Blocks of 10 MHz each may generate third-order distortion products spanning a significant 27 MHz. In short, broadcast and wireless broadband will demonstrably interfere with each other and that will be exacerbated by placing broadcast channels in close proximity to wireless users in the duplex gap.”

Aitken also cites a study by the European Broadcasting Union, “Can LTE Share Spectrum With DTT,” which found that cellular long-term evolution transmissions to be incompatible for sharing with direct terrestrial, or broadcast, TV.

The study concludes that terrestrial TV transmitters would have to be between 19 and 56 miles by land from a single LTE base station, depending on its characteristics, to avoid interference from that LTE operation. Given the greater likelihood of several LTE base stations all operating on the same frequency, a distance of between 124 and 184 miles would be needed.

LTE base stations also are vulnerable to interference from digital TV transmitters and would need between 124 and 372 mile of separation, depending on the transmitter.

The EBU study, “which investigated potential sharing of wireless LTE and broadcast spectrum similarly concludes that such sharing is impractical; LTE cannot share spectrum with digital broadcasting,” Aitken said. “These cautionary predictions should inform the commission as it seeks to repack broadcast channels in the duplex gap. Neither broadcasters nor wireless broadband users will find the sharing acceptable.”

Sinclair’s filing comes during the last days of the comment period on a previous commission Notice of Proposed Rulemaking on preserving one UHF channel in the TV band in each market for wireless microphones and unlicensed white-space devices. Opponents of duplex gap placement question potentially kicking a TV station out of the TV band to accommodate an undefined number of wireless mics and the minimal number of white-space devices. Comments are due on the docket Sept. 30.

It’s a given that there is going to be considerable “channel shuffling” after the upcoming television broadcast spectrum auctions. There also will be a lot less in the way of channel slots to choose from in the subsequent station repacking action. In 2014, the FCC adopted methodology for predicting interference between TV broadcasters and broadband wireless transmitters that are operating either in co-channel or adjacent-channel frequency slots. The commission termed their interference-prediction methodology, which is based on the Longley-Rice propagation model, “ISIX.”

Fig. 1: Derived from Fig. 23, page 453 of FCC document 14–50 dated May 15, 2014 by Stanley Knight
Click to Enlarge Looking at some cases where ISIX interference cases may come into play, suppose your station were to be allocated Channel 28 (center frequency = 557 MHz) in Scenario 7 (see Fig. 1). Your general manager might ask you to become a fortune teller and tell him whether this is a robust channel or a not so robust.

An ISIX interference situation may result if there two strong signals whose center frequencies are F1 and F2 and your center frequency is below F1 by the difference in frequencies F2–F1. IM3 falls in Channels N and N+3, if there are strong undesired signals on Channel N+K and N+2K. (K is an integer, either positive or negative).

For example, if there is a signal on Block A 619.5 MHz, (N+K) and a second signal is centered at 682 MHz, (N+2K) then F2–F1 = 62.5 MHz. Subtracting 62.5 MHz from F1 = 557 MHz, the center of your channel.

In this example F1 is in the blue area, meaning F1 is being radiated by a base station. F2 is in the yellow area, meaning this signal is being radiated by a cellphone.

INTERFERENCE CAUSES NOT ALWAYS APPARENT
Base stations radiate most of the time and their effective radiated power (ERP) approaches 1,000W. Cellphones briefly transmit and their ERP is less than 23 milliwatts. ISIX interference may result only when both F1 and F2 are transmitting simultaneously. Moreover, in this example F2 will be strong only if the cellphone is extremely close to the DTV receiving antenna. If either F1 or F2 is not strong, there can be no ISIX. However there are many base stations serving a given community, and many base stations will be found near interstate and other major highways.

Many viewers rely on an indoor antenna so your received signal power from these indoor antennas may be quite weak even when the receiver is not near your noise-limited coverage perimeter. Base stations are generally only a few miles apart. Therefore ISIX may be found around base stations.

While the first 600 MHz auction will auction 5 MHz blocks, after that most successful bidders will have acquired two or more blocks of 600 MHz spectrum. I expect that many of them will bid for contiguous blocks of 600 MHz spectrum so that they wind up with 10 MHz “super blocks,” which will be far more profitable than individual 5 MHz Blocks.

Fig. 1 shows that the spectrum for uplinks and down-links are equal for a given scenario. For Scenario 7, there are seven 5 MHz blocks for uplinks (cellphone Tx) and seven more for down-links (base station Tx).

This would allow up to three 10 MHz super blocks plus one 5 MHz block; or two super blocks and three 5 MHz blocks; or one super block and five 5 MHz blocks. For example, there could be three super blocks: A*B, C*D, E*F and one 5 MHz block, G. Or there could be super blocks B*C, D*E and F*G with one 5 MHz block A. There are many other combinations of 5 MHz blocks and super blocks 10 MHz wide.

The LTE signal bandwidth is 4.5 MHz for a 5 MHz block, and it will be 9 MHz for a super block of 10 MHz width. This means that the effective radiated power of a super block of 10 MHz is 3 dB greater than for a 5 MHz block. There is another subtle difference between the 5 MHz blocks to be auctioned initially, and 10 MHz super blocks. ISIX interference generated in a receiver is spread over 3*4.5 = 13.5 MHz. A 10 MHz super block will generate ISIX interference spread out over 27 MHz.

So the problem of ISIX interference to the reception of an ATSC signal will be far greater with super blocks (10 MHz wide) than with 5 MHz blocks for these reasons. However the FCC does not consider ISIX except for co-channel interference (CCI) or adjacent channel interference (ACI). Broadcasters should be concerned with the fact that ISIX interference can arise from signals offset in frequency by more than 6 MHz because the FCC will not consider offsets between DTV signals and LTE signals greater than 6 MHz. Two super blocks of 10 MHz each may generate third-order distortion products spanning 27 MHz! This is well known, but not recognized by the FCC as causing “harmful interference.” Where it happens the affected receive cannot look to the Commission or broadband operators for relief. This was pointed out in my June column “FCC ‘Harmful Interference’ Definition Gives Wireless a Pass” on www.tvtechnology.com.

ANOTHER INTERFERENCE EXAMPLE
Looking again at Fig. 1, you will note that the frequencies of LTE signals for a given block vary with the scenario number. Therefore you will need to know what blocks will be radiating LTE signals in your community. Whether the FCC will identify the scenario it applies for your market and your new channel number or just your channel number remains to be seen.

We will start with super block D*F whose center frequency is 639 MHz. F2 = 639 MHz. F1 is equally distant between Channel 28 and the center of super block E*F. So F1 = 0.5(639–557) = 598 MHz. This is in the green portion of the 600 MHz band, which for Scenario 7 is a TV channel (Channel 35). So here we have a hybrid of undesired signals, one LTE signal on super block E*F and DTV signal on Channel 35. Channel 35 will not cause CCI or ACI to Channel 28, so it is quite probable that there may be both Channels 28 and 35 in the repacking scheme for your community. But, there also may be ISIX to your Channel 28 signal from this combination of super block E*F and Channel 35 signals, however the FCC does not recognize such interference as being harmful interference.

With these facts, you will be able to answer questions about how your station will fare after repacking.

Charles Rhodes is a consultant in the field of television broadcast technologies and planning. He can be reached via email atcwr@bootit.com.

Charles W. Rhodes The FCC is proposing 11 scenarios for a 600 MHz Band Plan following the spectrum auctions. Which of these will be adopted will be determined by the outcome of the auction in 2016.

Each scenario for the 600 MHz band starts with Channel 21 (512–518 MHz). The highest channel number ranges from 26 to 44, depending on how much spectrum is offered for sale by broadcasters and then resold to broadband operators. The re-allocated spectrum is divided into blocks of 5 MHz each. There could be from two to 12 pairs of blocks. Pairs consist of one block for uplink transmissions from cellphones to base stations; and a second for downlink transmission by base stations to cellphones.

INTER-SERVICE INTERFERENCE
I have restructured the data in Fig. 1 into Figs. 2 and 3. Fig. 2 shows the number of UHF TV channels after repacking. It varies from 6 to 23 depending on how many pairs of 5 MHz blocks are re-allocated after the auction.

Fig. 1: The graph is Fig. 23 of the FCC's June 2 R&O, page 453. Light Blue: 5 MHz blocks of spectrum. Orange: Channel 37 reserved for radio astronomy and medical telemetry (hospitals). Diagonally shaded gray: guard bands. Blocks with numbers from 21–36 and 38–44 should be tinted light green. These are the remaining DTV channels. The numbers in a column on the left side are the amounts of spectrum broadcasters might offer to sell. The amount of spectrum that can be re-sold to broadband is less due to the need for guard bands in the 600 MHz band.

In Fig. 1, the striped cells with numbers of MHz; 11, 9, 7 or 3 represent the guard bands. There is an 11 MHz-wide guard band between the cellphone uplink blocks and the base station downlink blocks. There are also some smaller guard bands, notably, a 3 MHz-wide one adjacent to Channel 37; and a 7 MHz-wide guard band between some base station transmit blocks and DTV channels.

These guard bands are vital to protecting against what the FCC calls “Inter-Service Interference” or ISIX. Broadcasters are familiar with the fact that a DTV transmitter radiates power in both channels adjacent to the channel it is licensed to use. This is sometimes called sideband splatter, but it is actually third-order inter-modulation products generated in the high-power amplifier of a DTV transmitter; which gets past the transmitter RF mask filter and is radiated.

The 3 MHz guard bands on either side of Channel 37 (608-614 MHz), which is reserved for radio astronomy and medical telemetry, protect that channel from ISIX. The total bandwidth of all guard bands varies among the 11 FCC scenarios from 14 MHz to 28 MHz. I call such spectrum “lost” because, by definition, it cannot be used either by broadcasters or sold to broadband. Such spectrum is also lost as a source of revenue to the U.S. Treasury Department.

Fig. 2: Number of DTV channels after repacking as a function of the number of pairs of 5 MHz blocks available for auction.BEST LAID PLANS
I expect there will be pressure by white space advocates to let these guard bands also be used for white space services. That scares me because I recall the “good ol’ days” of Citizen’s Band mobile radios. Chaos soon reigned in the CB Band.

If the FCC chooses either eight or 11 pairs of 5 MHz blocks, it will have to purchase 28 MHz more spectrum from broadcasters than it will be able to resell to broadband operators. Since the commission is mandated not to lose money in these auctions, it will have to resell this spectrum at a price well above what it paid for the spectrum it purchased from broadcasters.

The 2012 law that authorized this auction requires the FCC to recover all costs of conducting it and requires the commission to turn over to the U.S. Treasury the net profits. I believe some of the billions of dollars expected from this spectrum auction will never be realized. I suspect that the estimated $44 billion of auction proceeds do not take into account the fact that some spectrum the FCC will buy cannot be resold because it must be used as guard intervals in the 600 MHz band plan.

The best case scenario from this perspective would have the FCC buy 84 MHz of spectrum and to resell 70 MHz of this spectrum. The minimum markup would be 84/70 or 20 percent. Administrative costs, the $1.75 billion to reimburse displaced broadcasters, and the profit for the U.S. Treasury will erode those billions of dollars promised to Congress.

Fig. 3: “Lost UHF Band Spectrum” in MHz. as a function of the number of pairs of 5 MHz blocks available for auction. Note the steep increase in “Lost Spectrum” between 7 pairs and 8 pairs of 5 MHz auctionable blocks. Fig. 3 plots the number of DTV channels in the 600 MHz band after repacking as a function of the number of pairs of 5 MHz blocks auctioned by the FCC. The outstanding feature of this plot is the steep decline in the number of DTV channels between the scenario with seven pairs of 5 MHz blocks (16 DTV channels) and the scenario with eight pairs of 5 MHz blocks. It would cost broadcasters four channels to allow one additional pair of 5 MHz blocks instead of seven pairs.

When all is said, it appears the best scenario identified by the FCC would provide seven pairs of 5 MHz blocks. This view has also been expressed by a number of cellphone operators according to the FCC.

CELLPHONE DESIGN
The FCC report provides a very complete analysis of each of the 11 scenarios depicted in Fig. 1 (FCC 14–50, p. 453). As Fig. 1 shows, there are guard bands of 3, 7, 9 and 11 MHz between different kinds or signals. The 11 MHz guard bands between uplink and downlink signals are obviously needed to keep the transmitter output from getting into the receiver input. The others are also required to avoid third-order distortion products from causing interference. For example, the 3 MHz band stop filters keep received signals in Channels 36 or 38 out of Channel 37.

Every kind of filter attenuates every signal within its pass band (insertion loss). With each 1 dB of insertion loss, the receiver’s noise figure increases by 1 dB, and sensitivity decreases by 1 dB. Worse yet, where there is more than one filter in the signal path, the insertion loss of each filter is additive. In Fig. 1, you will see that each scenario requires at least one 11 MHz filter and some require two or three filters. Filters not only cost in receiver performance, they cannot be manufactured as an integrated circuit so they take up space and add slightly to the weight of handheld cellphones. The fewer the number of filters in a handheld cellphone, the less it will cost and weigh, all things cellphone users can appreciate. As Fig. 1 shows, the number of filters varies significantly for the various scenarios.

There is yet another variable of importance not shown in Fig. 1, but was covered in the FCC report. The bandwidth over which the antenna of a handheld cellphone is efficient varies between the scenarios in the FCC Plan for the 600 MHz Band. Antenna efficiency directly affects battery life (time between recharges), as well as the sensitivity of the receiver. Scenarios that provide more than eight pairs of 5 MHz blocks will involve these antenna bandwidth problems. Where the efficiency of a simple passive antenna is poor (lots of signal bandwidth), the antenna can be automatically tuned to improve its efficiency. However this automatic antenna tuner feature requires added circuitry and therefore adds to the manufacturing cost. The insertion loss of this reduces the power to the antenna, which translates to increased power drain on the battery when transmitting. When receiving, it adds desensitization of the received signal.

Stay tuned.

Charles Rhodes is a consultant in the field of television broadcast technologies and planning. He can be reached via email atcwr@bootit.com.