13 New FCC AM Protection Rules You Need to Know!
Notes for risk and compliance managers
On 20 February 2014, a new day dawned for wireless and other users of towers and structural antenna supports. That’s when they became subject to new AM protection rules in the Federal Communication Commission’s (FCC) Third Report and Order and Second Order on Reconsideration in the matter of An Inquiry Into the Commission's Policies and Rules Regarding AM Radio Service Directional Antenna Performance Verification, MM Docket No. 93-177, FCC 13-115. In the Third Report and Order in this proceeding, the FCC harmonized and streamlined its rules regarding tower construction near AM stations.
AM broadcast interests and the FCC are on the march to improve AM RF signal transmission integrity. Within the last year the FCC has adopted a variety of new measures to benefit AM stations, and has open proceedings considering additional support and protection. In this atmosphere of AM activism, it would not be unreasonable to assume that these new antenna structure rules will be rigorously enforced. Since antenna pattern disruption often has a quantifiable economic impact on AM stations, civil litigation is a risk not foreclosed by the FCC actions here.
This report has been prepared to acquaint compliance and risk managers with, what is to many, a somewhat arcane subject. Much is not spelled out in the rules, which are only designed to address FCC compliance. There remain numerous legal liability and safety risks which are not in the FCC domain. The authors share some 75 years of experience in dealing with these and related issues, and submit that experience here to help the reader connect the risk dots, and to adopt suitable best practices going forward. No legal opinions are expressed or offered, and advice of experienced telecommunications counsel is recommended on such points.
Detuned Cell tower protects 5 tower 50kW AM Station WNCT
Regulatory Technical Notes:
In AM radio, the tower itself functions as the antenna. Consequently, a nearby tower may become an unintended part of the AM antenna system, reradiating the AM signal and distorting the FCC-authorized AM radiation pattern. The FCC’s old rules contained several sections concerning tower construction near AM antennas that were intended to protect AM stations from the effects of such tower construction, specifically, Sections 73.1692, 22.371, and 27.63. These old rule sections imposed differing requirements on the broadcast and wireless entities, although the issue is the same regardless of the types of antennas mounted on a tower. Other rule parts, such as Part 90 and Part 24, entirely lacked provisions for protecting AM stations from possible effects of nearby tower construction.
In the Third Report and Order the FCC adopted a uniform set of rules applicable to all services, thus establishing a single protection scheme regarding tower construction near AM tower arrays. The Third Report and Order also designates “moment method” (MoM) computer modeling as the principal means of determining whether a nearby tower affects an AM radiation pattern. This serves to replace time-consuming direct measurement procedures with a more efficient computer modeling methodology that is reflective of current industry practice.
These new FCC AM protection rules do not extend to the health and safety aspects of building antenna systems near AM broadcast antennas. In interacting with AM towers, some of the AM radio frequency power is also transferred to the new tower with the potential for injury to workers. All proposed installations near AM towers must continue to be evaluated for FCC and OSHA compliance with respect to maximum permissible exposure and shock and burn RF hazards, and the AM station(s) should be recognized in the site RF safety plan. Workers on such sites should also be trained in AM RF safety.
In short, AM protection rules have now been formalized and expanded to apply to all structures supporting, or proposed to support, antennas. Buildings are excluded, but towers and antenna support structures on top of buildings are now included. While sweeping in their applicability, the new rules lack much in practical application and conformance with AM rules now in place. Professional assistance is recommended to navigate those minefields, and this paper is intended to help flag them.
Essential New Rules Explained:
1) AM Non – Directional Antennas: 47 CFR 1.30002(a) requires a proponent of construction or modification of a tower within a specified distance of a nondirectional AM station, and also exceeding a specified height, to notify the AM station at least 30 days in advance of the commencement of construction. If the tower construction or modification would distort the AM pattern, the proponent shall be responsible for the installation and maintenance of detuning equipment.
Discussion
The FCC has designated criteria for notification of new structures or significant modification near non-directional AM towers. As shown in the figure below, any such structure situated within one electrical wavelength of the AM tower must be notified if it exceeds 60 electrical degrees in height. One wavelength is 984 feet divided by the AM frequency in megahertz. Maximum excluded height in feet is that result divided by 6. So, at one megahertz (1000 kilohertz) any structure exceeding 164 feet and within 984 feet of the AM tower must be notified.
It is important to note that exclusion from notification does not represent exclusion from AM station liability under the two year rule. The FCC has said “The new procedures were adopted in order to simplify the Media Bureau’s licensing procedures.” And, “For example, there may be circumstances in which a tower more than 3 kilometers away may affect a directional AM station. Similarly, a short tower which would otherwise be excluded from study may affect an AM station if it is very close.” Thus, to ensure knowledge of actual AM impact and proponent liability, a modelling study must be made.
If a determination is made that the AM non-directional pattern will be disturbed, then the structure must be detuned as discussed in Appendix D.
Any structure now detuned, regardless of height or location with respect to the AM non-directional tower must continue to be detuned, and any proposed change to the structure, its antennas, or feed lines must be notified to the AM, and the detuning readjusted after completion of the changes.
2) AM Directional Antennas: 47 CFR 1.30002(b) requires a proponent of construction or modification of a tower within a specified distance of a directional AM station, and also exceeding a specified height, to notify the AM station at least 30 days in advance of the commencement of construction. If the tower construction or modification would distort the AM pattern, the proponent shall be responsible for the installation and maintenance of detuning equipment.
Discussion
The FCC has designated criteria for notification of new structures or significant modification near directional AM antenna arrays. As shown in the figure below, any such structure situated within ten electrical wavelengths (not to exceed 3 kilometers) of the center of the AM array must be notified if it exceeds 36 electrical degrees in height. One wavelength is 984 feet divided by the AM frequency in megahertz. Maximum excluded height in feet is that result divided by 10. So, at one megahertz (1000 kilohertz) any structure exceeding 98.4 feet and within 9840 feet of the AM tower must be notified.
It is important to note that exclusion from notification does not represent exclusion from AM station liability under the two year rule. The FCC has said “The new procedures were adopted in order to simplify the Media Bureau’s licensing procedures.” And, “For example, there may be circumstances in which a tower more than 3 kilometers away may affect a directional AM station. Similarly, a short tower which would otherwise be excluded from study may affect an AM station if it is very close.” Thus, to ensure knowledge of actual AM impact and proponent liability, a modelling study must be made.
If a determination is made that the AM directional pattern will be disturbed, then the structure must be detuned as discussed in Appendix D.
Any structure now detuned, regardless of height or location with respect to the AM directional array must continue to be detuned, and any proposed change to the structure, its antennas, or feed lines must be notified to the AM, and the detuning readjusted after completion of the changes.
AM protection notification criteria for proposed structures
3) MoM Modeling: 47 CFR 1.30002(c) states that proponents of tower construction or alteration near an AM station shall use moment method modeling, described in § 73.151(c), to determine the effect of the construction or alteration on an AM radiation pattern.
Discussion
MoM modeling is a generic term for the analysis of characteristics of antenna systems by use of computer programs in which their physical properties can be numerically represented. The FCC does not require the use of specific software, and many variants are available in the marketplace capable of performing the required FCC calculations.
The development of analytical antenna models can be quite complex and two analysts can come up with different results depending upon their approach and experience. To keep uncertainly within reason, the FCC has set out certain limits and guidelines in Part 73.151 of the rules. Appendix A sets out some protocols relevant to antenna structure analysis. An experienced professional is usually required to make defensible MoM outcomes.
4) Directional Antenna Measurements: 47 CFR 1.30002(f) states that, with respect to an AM station that was authorized pursuant to a directional proof of performance based on field strength measurements, the proponent of the tower construction or modification may, in lieu of the study described in § 1.30002 (c), demonstrate through measurements taken before and after construction that field strength values at the monitoring points do not exceed the licensed values. In the event that the pre-construction monitoring point values exceed the licensed values, the proponent may demonstrate that post-construction monitoring point values do not exceed the pre-construction values.
Alternatively, the AM station may file for authority to increase the relevant monitoring point value after performing a partial proof of performance in accordance with § 73.154 to establish that the licensed radiation limit on the applicable radial is not exceeded.
Discussion
The large majority of AM directional stations are not licensed to use MoM proofs of performance. For those stations, nothing changes from present before and after field measurement procedures. As a practical matter, it is usually more prudent to use conventional methods to analyze the probability of detuning. If probable, to take pre-construction measurements, construct the tower, and install and adjust the detuning, followed by post- construction measurements to demonstrate effectiveness. It is usually slower and more costly to do preconstruction measurements, build the tower, take post-construction measurements, then install a required detuning system (requiring a tower crew return), and adjust it followed by new post-measurements (requiring return of the detuning tech team), all the while being unable to use the tower antennas!
The option to relicense the AM station monitor points will rarely be cost-effective, as it requires another set of field intensity measurements, often also requiring an engineering study on the AM station and filing of a Form 301 modification by the AM. This would only be essentially an add-on requirement if the proponent’s tower is very close to a station monitor point.
5) AM Station May Protest: 47 CFR 1.30002(g) states that tower construction or modification that falls outside the criteria described in paragraphs § 1.30002(a) and (b) is presumed to have no significant effect on an AM station.
In some instances, however, an AM station may be affected by tower construction notwithstanding the criteria set forth in paragraphs § 1.30002(a) and (b). In such cases, an AM station may submit a showing that its operation has been affected by tower construction or alteration. Such showing shall consist of either a moment method analysis or field strength measurements.
The showing shall be provided to (i) the tower proponent if the showing relates to a tower that has not yet been constructed or modified and otherwise to the current tower owner, and (ii) to the Commission, within two years after the date of completion of the tower construction or modification. If necessary, the Commission shall direct the tower proponent to install and maintain any detuning apparatus necessary to restore proper operation of the AM antenna.
Discussion
Proponents choosing to minimally comply with the AM protection rules by solely using the height and distance screens in the new rules must realize that they only enable compliance with the notification rules! They do not guarantee protection of the involved AM stations. The FCC said “The new procedures were adopted in order to simplify the Media Bureau’s licensing procedures.” And “For example, there may be circumstances in which a tower more than 3 kilometers away may affect a directional AM station. Similarly, a short tower which would otherwise be excluded from study may affect an AM station if it is very close.”
An AM station has one year to protest a situation existing before the new rules effective date, and two years for facilities implemented after that time. Preexisting submittals are clarified in Item (6).
Note that comments submitted by several major consulting firms in this proceeding proposed structure limits somewhat shorter and more distant than adopted by the FCC. The experience of the authors over decades of working with AM station regulation and protection supports the concerns of the commenting consultants, and provided a paper with similar concerns at the request of a commenting industry group. We do believe that proponents are greatly at risk of AM protests if they follow only the FCC notification criteria. We also note that the FCC has not chosen to foreclose any option of the AM for civil injunction or satisfaction.
6) AM Protest Submittals: 47 CFR 1.30002(h) states that an AM station may submit a showing that its operation has been affected by tower construction or modification commenced or completed prior to or on the effective date of the rules adopted in this Part pursuant to MM Docket No. 93-177.
Such a showing shall consist of either a moment method analysis or of field strength measurements. The showing shall be provided to the current owner and the Commission within one year of the effective date of the rules adopted in this Part. If necessary, the Commission shall direct the tower owner, if the tower owner holds a Commission authorization, to install and maintain any detuning apparatus necessary to restore proper operation of the AM antenna.
Discussion
This section makes clear the expectations of an AM station in filing a protest for reasons discussed in Item (5). It standardizes the required content of the showing, as well.
7) Non-conforming Tower Collocations Prohibited: 47 CFR 1.30002(i) states that a Commission applicant may not propose, and a Commission licensee or permittee may not locate, an antenna on any tower or support structure, whether constructed before or after the effective date of these rules, that is causing a disturbance to the radiation pattern of the AM station, as defined in paragraphs § 1.30002(a) and (b), unless the applicant, licensee, or tower owner completes the new study and notification process and takes appropriate ameliorative action to correct any disturbance, such as detuning the tower, either prior to construction or at any other time prior to the proposal or antenna location.
Discussion
This is quite straightforward, regardless of when a supporting structure was built; it must comply with the AM protection rules before any new antennas can be installed. This also means that, if a change is made to the structure after antennas are installed which renders it non-compliant; it also renders all existing antenna installations non-compliant and the licensees in violation until the problem is corrected. Such a problem could occur if the height is increased more than 5 electrical degrees. In such case, the notification process would need to be complied with. Another scenario would be the failure of an AM detuning system through damage or tuning drift. (See Appendix D for more). Obviously, these are serious matters for which the new rules provide no remedies; requiring immediate attention and FCC intervention by licensee communications counsel.
8) Collocations On Non-Directional AM Towers: 47 CFR 1.30003(a) states that when antennas are installed on a nondirectional AM tower the AM station shall determine operating power by the indirect method (see § 73.51).
Upon the completion of the installation, antenna impedance measurements on the AM antenna shall be made. If the resistance of the AM antenna changes, an application on FCC Form 302-AM (including a tower sketch of the installation) shall be filed with the Commission for the AM station to return to direct power measurement. The Form 302-AM shall be filed before or simultaneously with any license application associated with the installation.
Discussion
Wireless antenna collocation on AM non-directional towers is a well-established concept explained further in Appendix C. The new rules simply formalize and clarify the process of filing FCC Form 302 on completion of the installation.
It is not clear that notification is required, but it should be completed for the record, and in the event the AM (or AM’s) are themselves tenants.
9) Collocations On Directional AM Towers: 47 CFR 1.30003(b) requires that, before antennas are installed on a tower in a directional AM array, the proponent shall notify the AM station so that, if necessary, the AM station may determine operating power by the indirect method (see § 73.51) and request special temporary authority pursuant to § 73.1635 to operate with parameters at variance.
For AM stations licensed via field strength measurements (see § 73.151(a)), a partial proof of performance (as defined by § 73.154) shall be conducted both before and after construction to establish that the AM array will not be and has not been adversely affected. For AM stations licensed via a moment method proof (see § 73.151(c)), the proof procedures set forth in § 73.151(c) shall be repeated.
The results of either the partial proof of performance or the moment method proof shall be filed with the Commission on Form 302-AM before or simultaneously with any license application associated with the installation.
It is not clear that notification is required, but it should be completed for the record, and in the event the AM (or AM’s) are themselves tenants.
Discussion
Wireless antenna collocation on AM directional towers is a well-established concept explained further in Appendix C. The new rules simply formalize and clarify the process of filing FCC Form 302 on completion of the installation. It clarifies that either method of moments or field proof procedures shall be used, consistent with the AM station license status.
10) Modifications to existing towers: 47 CFR 1.30004(a) requires proponents of proposed tower construction or modification to an existing tower near an AM station that are subject to the notification requirement in §§ 1.30002 to provide notice of the proposed tower construction or modification to the AM station at least 30 days prior to commencement of the planned tower construction or modification.
Notification to an AM station and any responses may be oral or written. If such notification and/or response is oral, the party providing such notification or response must supply written documentation of the communication and written documentation of the date of communication upon request of the other party to the communication or the Commission. Notification must include the relevant technical details of the proposed tower construction or modification, and, at a minimum, also include the following: Proponent's name and address; coordinates of the tower to be constructed or modified; physical description of the planned structure; and results of the analysis showing the predicted effect on the AM pattern, if performed.
Discussion
For most situations, this rule merely restates the requirements of Items (1) and (2) and makes clear their applicability to existing towers.
Generally, on existing towers a change of less than 5 degrees in height, or addition or changes to antennas and transmission lines do not require notification. That translates to a height change of 7.7’ at the top of the AM band to a change of 25’ at the bottom. However, it does require a study to determine (a) if the change exceeds the permissible for the AM frequency(s) and (b) whether the height change puts the structure above the exempt height cap for that frequency(s).
Very important, if the tower is already detuned, or base insulated with isocouplers or similar devices, then any change to height, antennas, or transmission lines must be notified to the affected AM station(s). Measurements must be made before and after these changes, including adjustment of the detuning system, to assure that the AM station remains protected. See Appendix D for more on detuning.
11) Responses to notifications: 47 CFR 1.30004(b) requires that a response to a notification indicating a potential disturbance of the AM radiation pattern must specify the technical details and must be provided to the proponent within 30 days.
Discussion
AM stations should respond, in writing, as quickly as possible, indicating their agreement or disagreement. If they disagree, their response must contain the points of objection. With agreement, construction can go forward on its receipt. Construction cannot go forward until a disagreement objection is overcome. If the AM station does not respond within 30 days, the proponent may go forward with construction. However, it does not appear that the AM station forfeits its two year objection period by not responding. Thus, a proponent action which disrupts the AM operation remains a potential liability.
12) Expedited notifications: 47 CFR 1.30004(d) states that if an expedited notification period (less than 30 days) is requested by the proponent, the notification shall be identified as “expedited,” and the requested response date shall be clearly indicated.
Discussion
Much as (11), except that a requested response date is provided by the proponent and an oral response (followed by written confirmation) is acceptable. However, if the station does not respond or disagrees, the proponent may not begin construction until agreement is reached, or the non-response 30 day period passes.
13) Emergency notifications: 47 CFR 1.30004(e) states that in the event of an emergency situation, if the proponent erects a temporary new tower or makes a temporary significant modification to an existing tower without prior notice, the proponent must provide written notice to potentially affected AM stations within five days of the construction or modification of the tower and cooperate with such AM stations to remedy any pattern distortions that arise as a consequence of such construction.
Discussion
True emergency deployment of towers tall enough to trigger this provision is rare. However, the FCC is silent on deployments of COWs and other temporary special events structures which are not emergency-driven. They can, under appropriate circumstances have significant, albeit temporary, impact on AM station operation. A prudent approach would be to screen against AM protection criteria, provide an expedited notification as in (11) combined with discussions with the competent party at the AM station. Even if disruptive, short term issues can frequently be handled with the station obtaining an FCC temporary authorization (STA) or other mutually agreeable means.
Appendix A: MoM Analysis Protocols:
The FCC does not specify a particular method of moments analysis program or detailed procedure for making the AM protection analyses it requires. Instead, it specifies the maximum permissible limits of AM pattern distortion and refers the analyst to Part 73.151 of its rules to draw additional guidance from its MoM directional proof rules. Thus, compliance with the AM protection rules requires significant skill and experience on the part of the analyst to derive a defensible result.
Based on the long experience of the authors with AM antenna and propagation analysis acceptable to the FCC, a basic protocol is defined for guidance in carrying out the studies required here.
It is apparent from 73.151 that the FCC expects the MoM model to reasonably represent the structural physical characteristics of the modeled tower and its major appurtenances. It provides two ways of representing a simple tower structure; as a stack of fat cylinders of a diameter within certain constraints related to the radius of the structure, or as a matrix of fat wires representing tower legs and cross bracing. It specifies the particular constraints each must meet.
The first would be most appropriate to a monotube or uniform cross-section tower. The second to self-supporting lattice-type towers.
Top loading, such as by an antenna platform must be modelled. Lightning rod or beacon supports are considered part of the tower and should not be overlooked. If guy wires are used, and they are not proposed to be insulated, they must also be modelled. The amount of detail included in the model will depend upon the output required. For instance, a relatively course model may be all that is required if the outcome clearly demonstrates that detuning is or is not required. The more borderline the situation, or the higher the probability of the outcome requiring rigorous defense, as in civil litigation with an AM station, the finer the required analysis.
Unusual structures, such as power lines, water tanks, or tall signs are special situations for which MoM is well suited, but which require a good deal of skill and experience to be offered to the solution by the analyst.
Typical AM directional pattern by 73.150 method
FCC 73.151 rules out an array modeling solution unless a tower has a standard AM ground system. Few, if any, wireless towers have a ground system with some 30,000 feet of copper wire in the ground! However, assuming a best protection outcome for the protected AM station, the assumption of a perfect ground for the wireless structure is reasonable and accepted by MoM programs.
Similarly, because few wireless structures are situated on an AM array’s ground system, it is not possible to accurately model the tower into the AM array. The critical functions of the tower electrical spacing, electrical phasing, and coupling attenuation cannot be known without extremely detailed analysis of the intervening terrain for conductivity and dielectric constant. An assumption of perfect earth between them is not appropriate because the analysis result will be in error precisely because the ground assumptions are not actual case.
We believe that the preferred analysis is to derive the reradiation inverse field intensity value from the proponent’s structure as discussed above and to algebraically add it to the theoretical directional pattern values as derived in Part 73.150. The resultant is then compared to the licensed standard (or augmented standard) pattern in the FCC CDBS data base. If the result exceeds that pattern at any azimuth, detuning is indicated. For non-directional stations, the MoM output value is compared to the inverse distance field intensity from the CDBS data base. If the result exceeds +/- 2 DB of the CDBS value, then detuning is indicated. These results represent a best outcome for protection of the AM station.
Appendix B: Water Tank & Power Line Considerations:
Water tanks have frequently been utilized as antenna support structures. These structures now come under FCC AM protection regulations, and water tower owners themselves may be liable as “Commission authorization holders” even without antenna installations as licensees of SCADA transmitters and other radios. A particular concern is that many water towers have new antenna support structures installed atop them. These may trigger the 5 degree height increase rule, even if the water tower has been previously approved. If water towers and modifications have not been assessed and notified, with appropriate detuning actions, it is forbidden to mount antennas on them!
Similarly, power line towers and poles often have wireless antenna support platforms built on top of the existing structures. Small cells and DAS antennas may be attached to the poles themselves. It is not unusual for high voltage towers and distribution poles to exceed FCC screening limits. Proponents of such installations should note that some Public Utilities Commissions may also require AM protection. If these structures have not been assessed and notified, it is forbidden by the new FCC rules to mount antennas on them!
From an AM liability standpoint, power transmission tower usually cannot be categorized by the FCC’s simply screening methodology. This is because the overhead grounding and lightning protection wires typically interconnect several towers with the AM signal. Short towers, when MoM analyzed, will be found to appear much taller from an AM reradiation standpoint. AM protection usually cannot be achieved by detuning a single tower, but the detuning of multiple towers will be required.
It has long been known that high voltage transmission line structures (and even some distribution) can seriously degrade AM transmissions without these specialized RF detuning treatments. More detail is also available at https://lbagroup.com/blog/am-detuning-powers-up-new-york-high-voltage-line/. Since many power tower owners are now covered by the rules by virtue of being “Commission authorization holders”, and are also often aggressively offering antenna attachment rights, preconstruction right of way planning should incorporate identification of these potential problems, but existing plant is not immune. Liabilities may be both civil and regulatory. As reported in Electric Light & Power, the experience of CH2M Hill in overcoming a NY PUC block on energizing a new 345 KV line until AM signal protection was ensured is instructive: https://www.power-grid.com/td/detuning-engineers-curb/.
Appendix C: AM Colocation Notes:
As acknowledged in the new AM protection rules, the regulatory procedures for collocation of other antennas on both non-directional and directional AM antennas have now been codified. The practice has been successfully used by most carriers for several years. Two approaches are typically employed.
The “folded unipole” method employs a cage of wires, much like a detuning system, to permit the base of the AM tower to be grounded and allow the placement of wireless antennas and feed lines without further isolation. It may not be employed on directional AM stations licensed under the method of moments proof of performance.
The “isolation” method utilizes a special device at the base of the AM tower through which the wireless feed lines pass. While not disrupting the feed line performance at wireless frequencies, the isolator blocks the AM RF.
Selection of the proper method for any given collocation scenario requires an experienced analyst and the weighing of various factors attendant to both the carrier and the AM station. A discussion of the process can be found at https://lbagroup.com/services/am-colocation-cellular-pcs-wireless-antennas-on-am-towers-worldwide .
Typical AM collocation using the “isolation” method
Appendix D: Detuning System and Maintenance Notes:
The most frequent method of isolating an antenna structure from a nearby AM station is the installation of a detuning system. Typically, such systems comprise one to six vertical wires (foldwires) extending all or much of the length of the structure and insulated from the structure except at the top, where the wires are bonded to the structure. The wires are held several feet from the structure by a system of top and bottom support beams and intermediate fiberglass insulators. At the bottom of the structure, a cabinet is installed housing adjustable coils and capacitors to permit adjustment for minimum structure reradiation. As the stable physical condition of the detuning system is essential to FCC compliance, tensioning devices designed to compensate for temperature variations are also installed at the base of each vertical wire.
More information about a widely used detuning system is at https://lbagroup.com/products/detunipole-detuning-skirt-kit .
Modeling a proposed tower prior to construction or major modification is done to determine whether the structure should be detuned or not. While Moment Method Modeling is the recommended analysis method for towers that fall within the parameters outlined by the new FCC rules, it cannot be reasonably be used to confirm proper adjustment of the detuning system. The only method to confirm that the detune system is installed and operating properly is a visual inspection with field measurements before and after installation. On site adjustments to the detune network after installation are always necessary.
When an AM detuning system is installed, it is too often a “set it and forget it” procedure. Left undisturbed, that initial setting is possibly good for many years. Unfortunately, that happy state is rarely achieved on a communications tower. New FCC rules clearly restate the need for detuning maintenance. The Commission is emphasizing that this practice needs to be a regular and continuing responsibility of the owner.
Wireless professionals are well versed in cellular systems; however AM technology concepts are often not included in their education or experience. Thus, it’s easy to overlook detuning maintenance. AM detuning systems are entirely passive, have no failure bells and whistles, and their failure in no way affects the wireless carrier operation.
There is no required inspection period for AM detuning systems in the FCC rules; however, it is generally thought that a two year inspection and recalibration interval is appropriate. Of course, a special inspection is necessary if irregularities are noted in between times, major tower modification or antenna construction is undertaken, heavy ice or wind occurs, or the site is vandalized.
Since communications structures are frequently climbed for maintenance, equipment change out, and repair, detuning systems are often compromised. In typical situations foldwires are broken free from their supports, platforms and equipment are installed over foldwires causing them to short to the tower, standoff insulators are broken, foldwires become improperly tensioned, and cabinet tuning systems are vandalized. Any of these scenarios that cause a detune system to fail and place the structure proponent and all attached licensees to be in violation of the FCC rules.
About the Authors
Lawrence Behr is CEO of LBA Group, Inc., in Greenville, North Carolina and Chris Horne, PhD, PE, is the Chief Technical Officer for LBA Group. The two have over 70 years of experience in areas such as mobile communications, medium wave (MW) broadcast technology, and compliance related matters.
Mr. Behr was Chairman of the Wireless Communications Association (WCAI) AM Protection Subcommittee, a leader in an industry coalition supporting the FCC AM protection effort. He has served as an expert witness in matters relating to telecommunications infrastructure, regulation and allocations. He is a founder and a Fellow of the Society of Broadcast Engineers (SBE) and a Fellow of the Radio Club of America (RCA). He is an iNARTE Certified Electromagnetic Compatibility Engineer, holds the FCC First Class license since 1957, and is an SBE Certified Senior Broadcast Engineer.
