Most Popular Articles
Transmitter Control: Regulation and Implementation
The technology continues to evolve - and so do the FCC Rules.
I'd like to see a show of hands: How many of you have ever had the Commission call you and request an imme diate shutdown of your facilities? I thought so. In spite of its rarity (has it ever occurred?), the entire premise of the existing rules on transmitter control are based on this implausible scenario.
Not that anyone's complaining; but the current rules on transmitter control are by far the most lenient in the history of broadcasting. We have come a long way from 30-minute logging intervals and daily inspections. Technology has come a long way as well. About the only thing that hasn't come a long way is clarity in the FCC rules regarding transmitter control.
Not only is equipment much more stable than before, but the technological advances in computing have allowed many of the simple monitoring and control functions to be delegated to a microprocessor. Although still not too receptive to lightning hits, computer chips are seldom late for work, and rarely arrive with a hangover, so overall the switch to automated controls has been a net improvement.
These technologies encouraged the FCC to first accept the concept of Automatic Transmission Systems (ATS) in 1977. Early units were amazing combinations of instrumentation amplifiers and motor driven rheostats. As microprocessors became common, these too were placed into service.
The array of equipment available today ranges from extension meters and simple stand-alone dial-up systems to web-cams and Ethernet-integrated systems capable of 256-site control. Regardless of the technology employed, there are several basic concepts that must be considered.
Attended vs. unattended operation A station may operate attended, unattended, or a combination of the two. The FCC self inspection checklist states, "Attended operation consists of ongoing supervision of the transmission facilities by a station employee or other person designated by the licensee either at the transmitter site, a remote control point, or an ATS control point. Such supervision may be by direct observation and control of the transmitting system by a live person at the transmitter site or remote control point, or such supervision can be by automated equipment that is configured to contact a person designated by the licensee. In either case a live person must be on duty at a fixed location during all hours of broadcast operation where he or she can turn off the transmitter and can either monitor the station operating parameters or be contacted by the automated equipment that is monitoring the equipment. During attended operation, it is expected that the transmitter will be turned off by station personnel within three hours of an overpower or overmodulation condition that can cause interference that cannot be corrected within that period of time." superscript 1
On the other hand, the FCC states, "Unattended operation consists of using self-monitoring or automatic transmission system (ATS) monitoring equipment to control the transmission system, or alternatively, operation in the absence of constant human supervision with equipment that can operate for prolonged periods of time within assigned tolerances. In the former case, equipment must be configured to automatically take the station off the air within the required three-hour or three-minute (certain AM DA requirements) time periods after an out-of-tolerance condition arises. In the latter case, the licensee is required to make certain that the station is monitored frequently enough to ensure that station operation is corrected or terminated within the designated 3-hour time limit, but constant human supervision is not required." superscript 2
The Commission has been emphatic in stating that the rules permit unattended operation of the transmitter, but do not relieve the station of the staffing requirements of the main studio. Stated generally, for part 73 broadcasters, the main studio must be staffed by two full-time employees. (For more on this, see FCC Update on page 26.) Note that the FCC does not "require the main studio staff to monitor an unattended broadcast transmitter." superscript 3
Section 73.1350(b)(2) states that "transmitter control personnel must have the capability to turn the transmitter off at all times. If personnel are at a remote location, the control system must provide this capability continuously or must include an alternate method of acquiring control ...that operation [may] be terminated within 3 minutes." superscript 4 The problem with this rule is that it does not seem to directly address the situation where the station is operating unattended, that is with no control personnel.
Monitoring and Control Systems The broadcaster may choose among many differing schemes for transmitter control, which may be broken down into three major categories.
Local control, of course, is the simplest option. In the good old days, the transmitter meters had to be visible from the control point. This is why many studios had a transmitter in an adjacent room with a window. Some stations employed mirrors or TV cameras to meet this requirement. Later, stations were allowed to use extension meters, which, unlike most remote control meters, were active at all times. Under these rules the transmitter was required to be within 100 feet of the control point.
Remote control allows the location of the control point (typically the main studio) away from the transmitter site. The rules state that "The remote control system must provide sufficient transmission system monitoring and control capability so as to ensure compliance with Section 73.1350". superscript 5
ATS involves the use of monitoring systems that will contact an operator should an ongoing out-of-tolerance condition occur. If the condition is not corrected within a given time span, the equipment will shut down the transmitter. Many remote control systems may be configured for ATS operation. The FCC will allow a hybrid ATS/remote control-type system.
A fourth option is no monitoring whatsoever. The FCC allows the use of "equipment that can operate for prolonged periods of time within assigned tolerances." This option still requires periodic verification and the ability to shut down the equipment within the prescribed three-minute limit. Obviously, the broadcaster who chooses this option would not have a leg to stand on should the FCC detect an out-of-tolerance condition.
Telemetry and Control Links A multitude of options are available here, too. For control from a fixed point, stations often employ part 74 frequencies, FM subcarriers or subaudible tones on AM. Recently, 2.4GHz unlicensed spread-spectrum devices have become popular. Stations that employ return links that piggyback on the broadcast signal are at a considerable disadvantage when the station goes off the air. Dial-up control systems are popular, especially since they allow the use of floating control points and give the chief engineer direct access to the transmitter from any phone.
The use of dial-up control has been subject to controversy for many years. Finally, in the last revision to the remote control rules superscript 6, the FCC allowed that the public switched telephone network (PSTN) was reliable enough to replace dedicated full-time leased lines. However, the rules require that the phone line at the transmitter site be dedicated to that purpose. The problem relates to the requirement that stations be able to shut down within three minutes of a request by the FCC. If the station engineer has dialed in to check meter readings, the station's control point operator cannot access the remote control because the phone is busy. Therefore, if the phone line is not dedicated, an alternate method of transmitter shutdown must be devised. This could involve a second phone line at the transmitter site, or an audio fail-safe (2.5-minute time out), or an alternate signaling method. A very common (and reliable) method is to loop the transmitter interlock line through your STL receiver's squelch relay. One FCC staffer implied that a "well aimed cannon" superscript 7 would also meet this secondary fail-safe requirement, however this method is generally not acceptable to most zoning authorities.
It seems that when the FCC relaxes the Rules on an issue, some want to push things even further. The FCC has allowed landline (PSTN) dial-up control without backup shutdown capability under certain conditions. Not all mountaintop transmitter sites have telephone lines available. Cellular is an option, but do not confuse cellular with PSTN circuits. It is possible to have a cellphone-controlled transmitter "leave the service area." Because of the unreliability of cellular systems (especially during peak usage hours), I would suggest that any transmitter site that employs a cellular-linked control system use some form of ATS so that long-term (three hour) uncorrected conditions will trigger a shutdown. Furthermore, such a system should have a secondary means of shutdown, such as a silence-sense or STL squelch interlock. A station in Virginia has operated in accordance with the rules using a system like this during prolonged (five day) cellular outages.
If cellular is unreliable, how about the Internet? Think about how many times you have been unable to access the FCC Daily Digest website before pursuing this idea. While it might be an interesting experiment, a backup remote control or an ATS with a secondary shutdown capability would probably be necessary to ensure compliance.
Contact Person The current rules give broadcasters great flexibility in devising a remote control system that works for their specific situation. The consolidation of broadcast facilities has brought forth a need for centralized control, and this is now a possibility. The Rules do not allow a broadcaster to simply lock the door to the station and go away - or do they? Some small-market operators have declared their home as a secondary control point, but are these operators really at that location at all times? What if a station declares its operation unattended? It is not required to have a control operator; therefore it is not required to have a control point. Nonetheless, stations must meet the three-minute shutdown rule, and it is implied that they must (through informal means superscript 8) have a record with the FCC of a contact person that can shut the station down.
Because of these ambiguities, the SBE petitioned the FCC for a declaratory ruling in 1998, but nothing has been forthcoming. For their own legal protection it would seem prudent for stations operating in the unattended mode to at least supply a pager or cell phone number to facilitate contact with the station during those times.
A remote transmitter site with dial-up control is not required to have a secondary shut-down means if a dedicated phone line is used. However, A special waiver to that single-use phone line is permitted - the phone may be used by the station engineer while he is at the site, with the site under local control
Of course, while the engineer is on the phone, the FCC has no way to reach the station to ask it to shutdown. In fact, there are sites that occasionally are operated under local control and do not have a phone at all. It seems clear that inconsistencies in the application of the three-minute rule leave all stations vulnerable to problems should a station inspection occur.
The future The NAB Guide to Unattended Station Operation has a comprehensive section on the history of transmitter control regulation. This is a book that should be on the required reading list of any station considering unattended operation. It is interesting to see the progression of these rules through the years. ATS rules, which were very specific, have been generalized to the point where they have become hard to define. Certainly, anyone with an ATS or remote control system operating unattended would do well to simply declare it an unattended system based on stable operation using ATS or remote control features to enhance the operation of that system. This removes the higher obligations that are placed on those using an ATS or remote control system. Indeed, some fully staffed stations without ATS consider themselves operating unattended 24 hours a day.
This will practically set in place now what the FCC will inevitably do: eliminate any equipment specifications and simply require stations to operate within the prescribed limits. We saw this happen several years ago when the requirement for a modulation monitor was eliminated - now stations must simply stay within the FCC limits. Broadcasters need this change, or at least a response to the SBE request, to eliminate the confusion that these rules have spawned. There will always be stations that want to skirt the rules, but responsible broadcasters should not have to constantly wonder if they are meeting the letter of the law.
References superscript 1 FCC Bulletin EB-18FM, FM Broadcast Station Self-Inspection Checklist, January 2000 edition.
superscript 2 ibid.
superscript 3 ibid.
superscript 4 47 CFR 73.1350 (b)(2)
superscript 5 47 CFR 73.1400(a)(3)
superscript 6 Report and Order FCC 95-412, released October 23, 1995.
superscript 7 Harold Hallikainen quoting John Reiser, Insight on Rules #96, www.hallikainen.com/rw/insite/insite96.html.
superscript 8 Report and Order FCC 95-412, Paragraph 33, released October 23, 1995.
Acceptable Use Policy blog comments powered by Disqus
[an error occurred while processing this directive]
Today in Radio History
The history of radio broadcasting extends beyond the work of a few famous inventors.
Read each issue online in our Digital Edition Format in your Web browser.
EAS Information More on EAS
The feed provides feeds for all US states and territories.
Need a calendar for your computer desktop? Use one of ours.
Information from manufacturers and associations about industry news, products, technology and business announcements.
Browse Back Issues[an error occurred while processing this directive]
Also in the March Issue
- The "And More" of Automation
- FCC Enforcement Items to Watch
- Testing AM Antennas
- New Products
- Field Report: Cloud Microphones Cloudlifter CL-1
- New Products at the 2014 NAB Show
- Side by Side: IP Codecs