Friday, February 22, 2013

Review of Revised OET Bulletin No. 69, "Longley-Rice Methodology for Evaluating TV Coverage and Interference" - The Repacking Formula

There are eight issues targeted in the Commission’s review of the OET Bulletin No. 69 (Longley-Rice) software.  They are as follows:

1.      Population (census) data.  The DTV allotment channels assigned by the Commission (circa 1998) were based on 1990 Census data.  A number of years after that, they began to incorporate the 2000 Census data in coverage and interference studies.  They now propose to migrate to the 2010 Census data.  I think this is a good thing, since the 2010 Census represents reality more so than use of older census data.

2.       Terrain data.  Currently, most Longley-Rice software (including the Commission’s) uses 3-arcsecond terrain data.  The Commission now wants to use 1-arcsecond terrain data in order to provide more accurate results of coverage and interference.  This is also a good idea, in my opinion, because it will yield a result which closer resembles actual field strength in a given area.

3.       Correction of inaccurate engineering data in records of some stations.  This absolutely needs to be fixed.  I suggest that the Commission request a review by every station of its engineering record and submit any and all corrections.  I can’t tell you how many times I have seen obviously miss-rotated antenna data in CP records (and then carried through into licenses) and use of ERP in dBk instead of kW in license applications (flip-flopping the values in the 302 Form).

4.       Use of actual station elevation patterns in calculations.  Right now, the software assumes a standard elevation pattern for all stations’ antennas.  Since elevation patterns can be quite diverse, use of actual elevation patterns should yield a better depiction of actual signal level, at least on a theoretical basis.  I support the effort, but with reservation.  Based on results of field studies I have seen and participated in, calculated signal level bears little resemblance to actual signal level at particular locations.  This is because RF doesn’t always behave as predicted.  When an antenna is side-mounted on a tower, significant scalloping of the pattern can occur, resulting in peaks and valleys in the amount of radiated signal in a particular direction.  In addition, attenuation effects from manmade structures and vegetation is not factored into the equation.  There are dozens of reasons why we tend not to find a good correlation between predicted signal strength and actual signal strength, except in very general ways.  I also want to mention that nulls and maxima in elevation patterns affect signal levels relatively close to the transmitter site, where receivers tend to have line-of-sight and relatively high signal strengths (even in the elevation pattern nulls).  Finally, many stations use mechanical beam tilt in addition to electrical beam tilt, which significantly changes the power radiated in certain directions and out to significant distances.  I think that if the FCC truly wants a more accurate picture of what is going on in the real world, they need to develop a way to incorporate the use of mechanical beam tilt into the calculations.

5.       Depression angle calculation.  The Commission accidently accepted a mistake in the original software whereby calculation of signal at a given receive site used a depression angle to the transmitting antenna based on the latter’s height above ground rather than the difference between the transmitter site and receive site in terms of height above mean sea level.  This can cause a serious anomaly when the calculations are derived for mountainous areas.  This should be fixed, in my opinion.

6.       Precision of geographic coordinates.  The software presently rounds transmitter and receiver locations to the nearest second.  They now propose to round to the nearest 0.001 second.  Since most antenna sites have not been surveyed to that precision, I don’t really think this is going to make a difference in the real world.  But, hey, go for it if you think it will make things better.

7.       Establishment of a calculation grid.  I don’t really understand what they are talking about here and I am concerned that this might be the way they can get away with repacking stations into tighter spectrum confines.  So, unless somebody can explain to me why this is a good thing for broadcasters, then I am opposed to it.

8.       Treatment of error codes.  Right now, when the software goes bonk along a certain azimuth under calculation (usually along azimuths where the terrain is going through rapid fluctuations), it just goes ahead and assumes that there is coverage by the station in all of the cells where this error code comes up.  The FCC is asking if they should continue to allow the program to do this.  In a perfect world, I would ask the FCC to fix the problem with the software, but in the absence of that, I think it is a conservative (and potentially beneficial) approach to keep things the same (i.e. assume coverage in the error cells).  I say keep it the same.

The NAB came out with its initial comments on these potential changes to the software.  While they are not opposed to the concept of updating the software, they are unhappy that it is being done now, just before the auction.  Many stations have begun conducting coverage and interference analyses on their stations in order to determine whether or not to participate in the auction or to make sure they are not getting screwed by the repack (in terms of interference-free coverage they now have versus what they given on their new channel).  The results of all those studies would be useless if the changes to OET 69 was implemented now.  The NAB is lobbying for the Commission to make the changes after the dust settles with the auction and the spectrum repack.

The concern I have is that there will not be enough time between now and the auction to adequately evaluate the differences that the new and old software have on station coverage and incoming interference.  And, I would be afraid that the changes the Commission makes to the software would disadvantage the broadcaster in some way that would only be discovered after it is too late.  If I could cherry-pick the items that I could support now in the changed software, they would be: use of 2010 Census data, use of 1-second terrain data, correction of station data in the FCC engineering database, correction of the depression angle problem, and use of actual antenna elevation patterns in the calculations.  Numbers 6, 7, and 8 above are not worth consideration at this time.  And I am very leery of the calculation grid thing.

If you have any questions regarding my comments, please feel free to share.

Thursday, July 21, 2011

FCC Sets Deadlines For LPTV Conversion To Digital and Operation in Core Spectrum

If you own an analog or digital LPTV station (or television translator or Class A station) that operates on an out-of-core television channel (Channels 52 – 69), you will no longer be able to stay on the air after December 31 of this year. In addition, if you want to move to an in-core channel (Channel 2 through Channel 51), you have to find an available channel and file your displacement application by September 1, 2011, which is just around the corner. After that date, the Commission will no longer accept displacement applications from out-of-core stations. All of these dates and edicts can be found in the FCC’s recently released Second Report and Order on the subject:

The September deadline is reason enough to get hopping on finding an in-core home for your station, if you have any interest in extending the operation of the facility beyond the end of the year. However, there is another reason to consider submitting a displacement application to the FCC as soon as possible. A large number of applications for new facilities have been filed in the past two years. These filings, once granted, will reduce the available spectrum for a number of potentially displaced stations such as yours. A displacement application trumps an application for a new facility, but only while if the pre-existing application remains pending until the Commission grants your application (in which case, the application for the new LPTV station is dismissed).

For these reasons, you should consider filing a displacement application with the FCC and seek operation on an in-core channel. The application must specify digital operation, and you will have at least 36 months to construct on the new channel. In addition, if your station meets certain rural coverage requirements, you may be eligible for reimbursement of a significant portion of your construction costs by the NTIA. More information on that program is located on the NTIA web site (

In the 2nd R&O, the Commission also indicated that all analog LPTV stations must cease operation and switch to digital operation by September 1, 2015. An analog station can either file an on-channel digital flashcut application or a digital companion channel application on a different channel. If a companion channel is desired, it should be filed as quickly as possible for the same reasons stated above. However, it is important to note that a companion-channel application does not take precedence over an application for a new LPTV facility.

Smith and Fisher can provide services such as channel searches and the preparation of the engineering portion of the FCC displacement or companion-channel application. We also can determine if your other analog in-core stations would be eligible for a digital on-channel flashcut facility and assist in the FCC filing for such a facility, if eligible.

If you have any questions regarding this issue, please don’t hesitate to call me at 703-494-2101, or send me an e-mail ( You can find out more information about our firm on our web site, Twitter and Facebook.

Tuesday, June 21, 2011

RF Exposure Calculations For License Renewals

When I am asked to perform an RF calculation for an FM or television station, I gather some key pieces of information before I start. I need to know the effective radiated power of the station, the polarization of the signal (horizontal, elliptical or circular), the make and model of the transmitting antenna, its orientation (if directional) and its height above ground (or roof level, if mounted to a structure on a building). If I know the make and model of the antenna, I can usually find its elevation pattern either in my files or on the manufacturer’s web site. The elevation pattern allows me to determine the intensity of each side-lobe of the antenna pattern as well as its distance from the base of the tower.

The other very important fact that plays a part in the situation is whether or not the area surrounding the transmitter site can be considered a “controlled” environment. The Commission has separate RF exposure guidelines for controlled sites and uncontrolled (usually public) areas. The exposure guidelines are five times more strict for uncontrolled areas than they are for controlled environments.

The FCC considers a site to be controlled if two requirements can be met. First, the site must be secure from public access. This usually means a fence with a locked gate surrounding the transmitter building/tower compound or locked doors to all entrances to a building’s roof if your antenna is so mounted. As I mentioned in my previous blog, a locked gate across an access road to a site is not sufficient to consider the site as controlled, if hikers, bikers or ATV users can go around the gate or access the site from another path. The second requirement for a controlled site is that every person that enters the site must be trained in RF safety awareness. This means everyone, from station personnel to contractors to equipment/site maintenance people. If even one person accesses the site without such training, the site will be considered to be “uncontrolled” by the FCC and the stricter exposure standard will apply.

Once I am convinced as to which standard to apply in the case at hand, I conduct a study to see if there are other FM and television broadcast facilities operating at the same site as my client’s facility. Usually, stations within a few hundred feet of my client’s are considered. Although there can be RF contributions from other types of antennas (cell phone, two-way, microwave, etc.) at the site, their individual contributions are usually less than 1% of the FCC’s public exposure guidelines and can therefore be ignored.

I then perform my RF calculations and find the maximum power density value that would occur two meters (six feet) above ground from my client’s facility. I also compute the distance from the base of the tower where this maximum value is calculated to occur (and the direction, if a directional antenna is used). I divide the result by the applicable exposure standard for that frequency and type of environment in order to get a percentage of the maximum allowable value (MPE). There are three basic factors that result in high RF numbers. They are: high effective radiated power, low antenna height above ground (or roof), and frequency. With respect to frequency, FM and VHF television stations have the strictest exposure standard, because their wavelength is closest to the height of an average human being. Therefore, these frequencies are absorbed by the body much more efficiently than is the RF from a UHF station, which has a much smaller wavelength.

If there are no other co-located or nearby FM or television station antennas in operation, I am unconcerned as long as my client’s contribution to the RF environment is within 80 to 90 percent of the applicable maximum guideline value. If there other FM or television stations operate from the site, I am finished with my study if my client’s maximum calculated contribution to the RF environment is less than 5% of its guideline value. That’s because the FCC considers a station to be liable for fines and employment of RF mitigation techniques only if its RF contribution in an area of concern is greater than five percent. Since calculations are based on some very conservative assumptions and since I tend to find lower RF numbers in the field when I make measurements, I feel comfortable in claiming that my client’s RF contribution can be excluded from consideration if I calculate it to be less than five percent of the applicable standard.

If I calculate a number greater than 5 percent and there are other stations at my client’s site, I have to perform a similar calculation for each of the other stations. If I assume that each station’s RF maximum value occurs at the same point (which they don’t) and the total calculated RF is significantly less than 100 percent of the MPE, then everything is peachy.

If the number is close to or greater than the MPE in any of the above situations, I usually suggest that a power density survey of the site be conducted. In my next blog, I will talk about surveys and some things I have learned from doing more than 100 of them.

If you have any questions or would like us to help with the RF portion of your renewal, please call or send an e-mail to

Wednesday, June 1, 2011

RF Compliance Certification For FCC License Renewal

According to our friends at CommLawBlog, the FCC has revised its Rules with respect to a broadcaster’s certification of compliance with the Commission’s human exposure guidelines to non-ionizing electromagnetic radiation (RF) in its license renewal (Click here to see their take). In past renewal cycles, the broadcaster was required to submit a technical statement from an engineer, showing calculated or measured compliance with the RF exposure limits. In this round of renewals, a broadcaster can simply check a box on the renewal form that indicates that the RF environment surrounding the transmitter site has not materially changed since the last renewal cycle.

For a stand-alone broadcaster at a particular transmitter site, this is a no-brainer. Unless the station has changed its transmission facility since the last renewal and there has been no construction of residences, commercial buildings or tower structures in the vicinity of the transmitter site, there should be no change in the ground-level RF situation. If changes have been made to the transmission facility or if structures have been constructed in the vicinity of the site, new RF calculations should be made in order to ensure compliance with the FCC’s RF exposure Rules.

Most broadcasters operate at sites where there are other broadcast antennas. Such a complex RF environment requires more careful consideration. If there have been no changes to any of the broadcast facilities that have been operating there since the last renewal and there have been no additional broadcast facilities constructed at the site or an adjacent site, and no construction of new structures within close proximity to the transmitter site, the “No Change” box can be checked on the renewal form regarding RF certification.

Lately, the FCC has been ramping up its on-site inspection of stations that are believed to be exceeding the RF exposure guidelines. If the FCC finds that a station is indeed exceeding the allowable limits, the fines are severe and the Commission requires immediate rectification of the situation (including going off the air until an effective solution can be determined). If an inspector finds an area surrounding a particular transmitter site that exceeds the human exposure guidelines, the FCC considers a station liable for fines and mitigation techniques if its contribution to the RF situation in the area of concern is more than five percent (5%) of its particular guideline value.

Let’s say that you operate a broadcast antenna in an antenna farm. In a particular area of the transmitter site, the total RF from all sources at the time of last renewal cycle was 97 percent of the allowable standard. Let’s also say that the RF contribution from your station was 50 percent at that spot. Suppose that last year, a new FM station went on the air at the site. In the area of concern, the RF level is now 120 percent, well over the FCC’s allowable limit. If an FCC inspector measures the RF level in this spot, the Commission would fine your station and require you to take remedial steps to bring that area into compliance. And you hadn’t made any changes to your operation.

One other point regarding RF exposure needs to be made here. The FCC has two different exposure standards. The standard for public areas is five times more strict than it is for “controlled” sites. The definition of a controlled site has two requirements. First, it must be inaccessible to the public. For broadcaster’s that operate from a building rooftop, all points of entry onto the roof must be locked. For tower sites, this means a chain link fence with a locked gate surrounding the transmitter compound and tower. A gate across an access road is not sufficient if hikers, bikers and/or users of ATV’s can reach the site. The second and most overlooked requirement is that all those that access the transmitter site must be trained in RF safety practices. This applies to HVAC mechanics, window washers (for building sites), electricians, janitors, waste removal personnel, food service personnel, and, of course, all station personnel. The onus is on all of the broadcast users of a particular site to make sure that all contractors and employees that access the site have such training, otherwise the Commission will deem the site “uncontrolled” and the public RF exposure standard will apply.

If you have had a power density survey performed at your site, review the report and make sure that nothing has changed at the site with regard to the stations that operate from the site. Check and make sure that any RF warning signs that were installed are still visible. And, check to make sure that fencing and locks on gates are intact.

Finally, if you have any doubts about whether or not you comply with the RF exposure standards, contact an engineer. We can perform calculations for your station as well as conduct power density surveys of broadcast sites. We have RF meters that can determine overall RF levels in specific areas as well as individual station contributions in multi-station environments. In addition, we provide RF safety training classes for those that need to access your site.

Friday, May 27, 2011


Well, the transition from analog television transmission to digital ended nearly two years ago and a lot has been learned since then. In the early days of analog operation, most television stations operated on Channels 2 through 6 (low-band VHF channels) and Channels 7 through 13 (high-band VHF channels). These stations had significant coverage, indoor and outdoor, for miles from the transmitter site. As that spectrum became congested, Channels 14 through 69 (UHF channels) were allocated to new analog television stations. Due to the fact that UHF stations required 10 to 20 times more power than VHF stations to cover market populations, they were the poor step-children of the television spectrum. In addition, since the network programmed stations (ABC, CBS, NBC and eventually FOX) had the VHF channels in most major markets, the UHF channels were home to more of the niche programmers. As a result of these issues, many VHF stations decided early on in the digital allocation game to stick with their analog channels, convert them to digital and give back to the FCC their digital UHF allotments at the end of the transition. Channel branding and lower operating costs were usually quoted as the main reasons for keeping their original analog channels.

One of the biggest concerns that has emerged, since the end of the transition, is the inability of these digital VHF stations to cover all of the viewers of the original analog station. One reason is that digital signals do not exhibit analog’s “graceful degradation” as one approaches the edge of the coverage area. Either there is enough signal to translate into a picture or there isn’t. In addition, it is now clear that the FCC’s planning factors did not adequately provide for enough power for VHF stations to even come close to covering their old analog audience (especially east of the Mississippi River). The reason for this is probably that the FCC needed to restrict power levels of such stations in spectrum-congested areas of the country in order to allot every station a second channel for digital operation prior to the end of transition. Not only are the power levels restricted, but the required level of signal for outdoor reception of a digital VHF station are severely over-stated by the FCC. Adequate reception of a 36 dBu signal from a Channel 12 station would probably require a high-gain outdoor antenna mounted 30 feet above the ground, pointed at the transmitter site, have no intervening impediment (terrain, building or vegetation) and at least one signal booster in the receive system. These are unreasonable go/no-go requirements for most viewers living at the edge of a station’s service area.

Since most digital VHF stations have maximized their effective radiated power values, there are not many options to improve station coverage. The exception is the addition of a vertical component to their existing facilities, if they are presently operating with an antenna that is horizontally polarized. The addition of a vertically-polarized antenna to the existing transmitting facility, if properly designed, can increase the coverage of the station in a couple of ways. For indoor reception, the addition of a vertically polarized signal to the present horizontally polarized signal can double the signal density at the receive location and reduce the need to optimize the receive antenna in a particular direction. In addition, service at the fringe areas of the station’s coverage can be improved due to rotation of the vertical signal into the horizontal plane as it travels along the earth. Since most outdoor antennas are horizontally polarized, more signal can be picked up by the viewers in the fringe area.

The three down sides to adding a vertically-polarized antenna to an existing VHF facility are: the supporting structure (tower) may not be able to handle the additional antenna, either from a space or a loading standpoint (or both); the vertical antenna must be properly phased with the horizontal antenna in order to avoid causing interference to the latter; and, additional transmitter power, a significant cost factor, is required for the vertically-polarized antenna.

Besides the coverage benefits of adding a vertically-polarized antenna to the existing system, the addition of the antenna does not require prior approval from the FCC as long as the power in the vertical component does not exceed that authorized to the station. Once the new antenna is added and becomes operational, a 302-DTV (license application) is filed with the new parameters within ten days.

Monday, October 25, 2010

Rooftop RF

As I travel around the Washington, D.C., area, I can’t help but notice the tremendous number of buildings that have numerous antennas mounted to the roof. I wonder if anyone has considered the overall RF to which workers that access these roofs could be exposed. Workers such as window washers, elevator mechanics and HVAC service personnel, just to name a few. If the RF situation on the roof has not been measured, the roof of such a building would be considered by the FCC and OSHA to be an uncontrolled environment and a significantly stricter RF exposure standard would apply. As a result, I believe that many of these buildings would not meet the tougher exposure guidelines in certain areas. While the owners of the transmitting antennas would bear the entirety of the FCC’s and OSHA’s fines and mitigation techniques, the building owner would undoubtedly be sucked into any lawsuit brought by a worker that believed that the antenna owner and building were negligent with respect to an RF exposure issue.

A power density study would provide a measure of safety to the building, its workers and the antenna owners. Such a measurement survey would identify areas of the roof that workers should avoid and how the building/antenna owner should mark these areas (usually chained off and RF warning signs attached to the chain). The study also determines the major contributors to the areas of concern so that these antennas can be taken off the air if these areas need to be accessed by workers for maintenance or repair.

Smith and Fisher has state of the art power density meters which can measure total RF levels in any area and can identify the specific major RF contributors in areas of concern.

Thursday, May 27, 2010

Analog LPTV Stations

We have just returned from the National Translator Convention, where members of the FCC urged LPTV and translator station owners who operate analog-only facilities to apply for digital operation either on the present channel (“flashcut”), file for a digital companion channel (which would allow both analog and digital operation for the time being), or a displacement application specifying operation on a new in-core channel (Channels 2 – 51). There are three reasons to consider submitting such an application to the FCC as soon as possible. First, large numbers of applications for new facilities in rural markets are being filed every day. These filings, once granted, will reduce the available spectrum for flashcut, companion channel and displacement proposals from existing analog stations. Second, the Commission is going to open a filing window for the major television markets in July. It is expected that a significant number of applications will be filed at that time. While an existing analog station might not be located in such a market, any application for a new LPTV facility that will be located within 70 miles or so of the existing analog facility could preclude consideration of that channel for flashcut, companion channel or displacement purposes. Third, the FCC has indicated that it may soon set a hard deadline for translators and LPTV stations to cease analog operation.

For all of the above reasons, analog stations should consider filing a digital application with the FCC sooner rather than later. Once granted, the station will have three years to construct the digital facility. Two 6-month extensions of the construction deadline can also be requested of the Commission.

It is also important to note that, if the station meets certain rural coverage requirements, it may be eligible for reimbursement of a significant portion of the digital construction costs by the NTIA. More information on that program is located on the NTIA web site (