Revisiting Unattended

Radio World - 1/21/98

by Harold Hallikainen

San Luis Obispo, CA - In November 1994, the FCC adopted a Notice of Proposed Rulemaking under Mass Media Docket 94-130. After considering comments, the FCC released a Report and Order [FCC 95-412] establishing the current rules authorizing unattended operation of broadcast transmitters and changing the requirements for attended operation.

This article provides a brief overview of the current status of the rules. Additional information is available from several sources. The NAB has published a book (by me) entitled the NAB Guide to Unattended Station Operation. It is available from the NAB at +1 800 368 5644. You can also order it on the web at The FCC has released an Unattended Operation Frequently Asked Questions list. It is available at For those without web access, the FCC's FAQ is available at my Fax On Demand (+1 805 541 0201). This article is available with links to most citations at And, finally, a hypertext version of the FCC Rules is available at

The Rules now allow for several modes of transmitter operation. These can be summarized as:

  1. Attended
    1. Direct Control - Operator at transmitter site.
    2. Remote Control - Operator at control point, "polls" transmitter to insure correct operation, and manually makes adjustments or mode changes.
    3. Automatic Transmission System - ATS monitors and adjusts transmtter. ATS notifies operator of out-of-tolerance alarm conditions. ATS need not automatically shut down transmitter
  2. Unattended
    1. Automatic Transmission System - ATS monitors and adjusts transmitter. ATS shuts down transmitter within three hours of an interference causing condition occuring. The shutdown is reduced to three minutes if the condition is the transmitter operating in an unauthorized mode for the time of day (such as an AM that does not switch pattern or reduce power). There is no ATS alarm requirement with unattended ATS, as there is no operator to receive the alarm.
    2. Stable Equipment - The FCC does not require ATS for a station to operate unattended. If the station determines that the transmission equipment can operate for long periods of time without human supervision, the equipment can operate unattended without an ATS.

For simplicity, I've used the traditional term operator to refer to the person (if any) in control of the transmitter. Prior to 1995, licensed operators were required to be in charge of broadcast transmitters. The current rules allow transmitters to be controlled by employees of the licensee or others designated by the licensee [73.1400(a)]. No operator licenses are required.

While the FCC has eliminated the term transmitter operator, stations are still required to have a chief operator. The chief operator is responsible for the completion of various duties (these may be delegated, though the chief operator remains responsible). Among these duties are equipment inspection and calibration, AM monitor point field strength measurements, AM and FM equipment performance measurements (occupied bandwidth), and a weekly review of the station log. [73.1870(c)]. The chief operator of an AM directional station or an AM nondirectional station with authorized power greater than 10 KW must be an employee of the station. The chief operator of other radio stations may be an employee or a contractor. So, while the new rules do not require operators, chief operators are required.

Aim a cannon at the transmitter

Prior to adoption of the current rules, many stations were using dial-up (public switched telephone network or PSTN) circuits for transmitter control, since the FCC had dropped the previous "fail safe" requirement. An FCC staff member advised stations to have some alternate means of shutting down the transmitter should the PSTN circuit fail. He suggested use of an STL carrier sense relay, program silence sense, a dedicated part 74 radio link, or the use of a well aimed cannon. There had to be some way to shut down the transmitter. In the Report and Order establishing the current rules, the FCC declared that the PSTN is reliable enough for transmitter control. No backup circuit is required provided the PSTN circuit is available full-time for use of the transmitter control or ATS system. [FCC 95-412 paragraph 40] However, the FCC points out that since one never knows when an operator needs to contact the transmitter site or when the transmitter site needs to report an alarm (under attended ATS), the PSTN lines should not be shared. Based on this reasoning, it would appear that under remote control you could share a PSTN line at the control point, since the remote control is not required to initiate alarms. The operator must be able to hang up on the person requesting a song to call the transmitter site. Under attended ATS, however, the control point PSTN line must be dedicated to receiving alarms from the ATS, since those alarms cannot be scheduled.

At the transmitter site, a PSTN line can generally be easily dedicated to transmitter operation unless the chief operator is there and wants to order a pizza. The FCC states in question 4 of their FAQ that the line may be used for other purposes when the transmitter is being controlled by someone at the transmitter site.

Contact Person

In paragraph 33 of the Report and Order [FCC 95-412], the Commission decided against establishing a contact person database. In paragraph 34 they decided against a requirement that stations post contact person information (as is required for translators in 74.765 and 74.1265). Indeed, it appears that unattended stations may be truely unattended, with no contact person or on-call person. It is left to the station licensee to determine the amount of human supervision the transmission system requires. However, this does not excuse a licensee from keeping its transmitter parameters within tolerance.

FCC Comments

At deadline, I received a response from four FCC staff members. I appreciate their speedy response! One representative from the St. Paul field office told me that he has seen very few stations running unattended, especially since they normally inspect the stations during the day. He thought my interpretation of the PSTN reliability statement in the rules was correct. I also had email correspondence with an inspector who is part of the FCC's alternate broadcast inspection program. He said that stations are required to have "absolute control" and that the PSTN was not enough without some alternate means of shutting down the station. Comments from the FCC in Washington indicate the a PSTN line used for no other purpose than remote control is sufficient without an alternate means of shutting down the transmitter.

The FCC also stated, quoting from the FAQ, that "unattended station is fully automated such that the transmitter will be shut down if an out of tolerance condition arises." This definition implies an ATS requirement for unattended operation, which conflicts with paragraph 8 of the Report and Order [FCC 95-412].

The FCC also pointed out that unattended operation does not prevent station inspections at any time the station is on the air [73.1225(a)]. They, therefore, suggest that the FCC be notifed by letter of contact persons and telephone numbers. This, however, conflicts with paragraph 33 of the Report and Order [95-412]. There, the Commission decided against a contact person database, relying instead upon "existing informal procedures" to contact station personnel. In their comments, the FCC points to section 73.1350(g), which requires the station licensee to notify the FCC in Washington within three days of the initial use of a control point. While this appears to apply to attended remote control stations, it does not (to me) appear to apply to unattended stations, since they are not required to have a control point (or an operator).

More to Come

This article is already too long (my apologies to the editor). I will be making a presentation on unattended operation of broadcast transmitters at the upcoming NAB convention. I should have more information on FCC enforcement activities in this area by then. In addition, an upcoming article will provide a more thorough discussion with the FCC field inspectors providing their viewpoints.

Harold Hallikainen is president of Hallikainen & Friends, a firm specializing in electronic design and technical writing. He is also an avid contra dancer. He can be reached at +1 805 541 0201 (voice/fax),, and Wide Web).