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.

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 (http://www.ntia.doc.gov/lptv/index.html).

Notes from the National Translator Convention in Reno, Nevada

According to Hossein Hashemzadeh of the FCC’s Media Bureau, the July 26, 2010, date for the removal of the geographic restriction on the filing of new LPTV and translator applications is still on track. At present, applications for new stations are limited to those that specify transmitter sites that are located at least 75 miles from the center coordinates of the top 100 television market cities. The Commission has not allowed applications for new facilities in the major markets since 1991.

Up to two six-month extensions of expiring LPTV/translator digital construction permits will be granted by the FCC to flashcut, companion channel and displacement authorizations. Extension requests should be filed 60 days prior to the expiration date of the construction permit. The “easy” extensions do not apply to authorizations for new digital stations. Tolling requests, which, if granted, effectively stop the 36-month construction requirement clock, can be filed for CP’s for new facilities, based on circumstances beyond the control of the permittee, Acts of God or severe financial crisis.

This summer, the FCC plans to hold a technical forum to explore the possibilities of increasing the power limits for VHF television stations. Many full-power VHF DTV stations find that they are not replicating their analog coverage areas and have lost significant audience since the end of transition. I believe that one possible way to accomplish the increase would be to allow stations to cause up to 2% interference to other stations (as opposed to the present 0.5% interference limit). Since most VHF stations do not realize actual coverage at the edges of their predicted service areas, where most of the predicted interference occurs from other stations, such an increase in interference would probably not result in actuality. Alan Stillwell of the FCC’s Office of Engineering and Technology presented a paper in which field studies indicated that the amount of signal required for indoor reception of a high-band VHF DTV signal is 62.8 dBu, or about 100 times stronger than the FCC’s predicted city-grade service requirement (43 dBu).

Mobile/handheld video reception will require more signal strength than is needed for standard television reception. This is partly due to the fact that most mobile devices will be held only a couple of meters above ground (at most), whereas most standard propagation models assume a receive antenna that is mounted 10 meters (30 feet) above ground. The difference in signal strength due to the different receive antenna heights is significant (on the order of 10 dB). Stations that want to provide mobile video streams should consider adding a vertically-polarized component to their transmission system, since the receive antennas for handheld devices are typically vertically polarized.

The owner of a translator station that wants to change its status to a Low Power Television station (or vise versa), simply needs to send an e-mail request to Hossein Hashemzadeh at the FCC (Hossein.Hashemzadeh@FCC .gov). The change will be noted in the database, even though the file number prefix for any of the previously filed applications will not show the change.

Hossein Hashemzadeh, of the Media Bureau of the FCC, said that cancelled or expired construction permits and dismissed applications must be purged from the Commission’s engineering database by hand (his). He typically goes through the database every 6 months or so. However, if someone notices that a particular dismissed application or expired CP needs to be removed from the database, they can send an e-mail notification to Hossein and he will manually delete the entry from the engineering database.

There are still over 400 LPTV and translator stations that are operating on out-of-core channels and have yet to file displacement applications to seek in-core channels or have not filed for digital companion channel facilities with in-core channels. The Commission is urging stations to apply for such channel-changes as soon as possible due to the final build out of wireless communications facilities and safety service facilities, which will require out-of-core stations to go off the air with relatively little notice.