RF Radiation Exposure References, Tower Lights

Radio World, 10 April 1991

by Harold Hallikainen

Last month we finished up my opinions on what could be done to insure compliance with the FCC specifications for human exposure to radiation. Additional information sources are listed in table 1.

In addition, I made lots of phone calls in writing the series. Most of those I spoke with (and you may wish to speak with) are listed in table 2. I'd like to thank all those who helped!

Tower Lights

The FCC has recently issued several substantial fines for inoperable tower lights. They know tower lights are going to fail and have no problem with this. The problem arises when no one knows the tower lights are out. Each station (having a lit tower) is required to make a daily inspection of the tower lights or tower light indicator, or have an automatic alarm that will report the failure of any lamp. If a station is complying with the daily inspection requirement, it is hard to see how the FCC can find the lights out with the station being unaware.

If you find a steady burning top light or any flashing beacon has failed, the FAA is to be notified within 30 minutes of the observed outage. Since the lights are only required to be observed once a day, this may be up to a day after the actual failure. They are actually giving us some leeway by not requiring an automatic alarm. The FCC generally expects defective tower lights to be fixed within a few weeks. Although not specifically required, it is suggested that the results of ALL tower light inspections be logged in the station log. You ARE required to log the failure (and restoration) of any lamp (see 17.49).

I've seen cases where the FCC found improper tower light operation and the studio indicator said the lights were operating properly. 17.47(a)(1) requires tower light indicators to properly detect the failure of ANY lamp (whether failure of that lamp is required to be reported to the FAA or not). Further, 17.47(b) requires a quarterly inspection of all the control devices, indicators and alarms to insure they are operating properly. I'd suggest such an inspection include a simulated failure of a lamp. Can the operator detect the failure? You can easily simulate a failure by adding one 116 watt lamp to the lighting circuit after the current sampling transformer. AM stations might have a light in the tower coupling unit that is always on (this also prevents condensation in the cabinet). To test the tower light indicator, turn this lamp off. This would give the same indication as the failure of a steady burning side light. FM stations might have a transmitter site "night light" that serves the same purpose. I've seen too many stations that just calibrate the remote indication to peak at 100% when everything is operating properly. The operator can identify the failure of a flashing beacon, but that's about all.

Suggested Tower Light Inspection

Once a lamp is added to allow simulated failures, I'd suggest operators (or system software, in programmable systems) observe the minimum and maximum indication over a one minute period. As an alternative, a system could include the tower light indications in a scan of all meter readings and accumulate the minimum and maximum indications over ten samples. A limit chart (or evaluation routine) can be prepared based on the lighting load. If you have a typical tower lighting load (two 116 watt steady burning side lights, one "extra" 116 watt steady burning lamp, two flashing 620 watt lamps), a decrease of the minimum to 67% of the typical minimum (probably use 84% of the typical minimum as a threshold) indicates the loss of one steady burning lamp (though we don't know which one). A decrease of the typical maximum to 61% of typical maximum (probably use 80% as a threshold) indicates the loss of one flasing lamp. In addition, a very high minimum would indicate the flasher is stuck on, while a very low minimum indicates the flasher is stuck off (or both lamps failed).

During the daily inspection, the operator should log the minimum and maximum indication observed for each tower along with the evaluation of the results (such as "all ok", "one beacon lamp out", etc.). If a detected failure requires notification of the FAA (as described above), that should be done, and a notation made. I'd try to make the notation traceable. Who at the FAA took the information, etc.

Catch Problems Before The FCC

The vast majority of the violations I've found in my review of FCC files should have been caught by the chief operator. I've been working with NAB on a book to help the chief operator catch the problems before the FCC does. The book contains inspection forms based on FCC inspection forms. The book should be available by the NAB Convention. Again, the FCC Rules recognize that equipment will fail. There is almost always a way for you to stay on the air while making repairs. The failure of the equipment is to be logged. Diligent progress must be made towards making the repair. One station was fined for having its tower lights out for over ten years. That was not good progress.

See You At NAB!

Along with the sessions on fancy new emerging technology, NAB will have lots of sessions of concern to station chief operators. These include sessions on contract engineering, EBS, FCC rules, etc. I'll look forward to seeing you there!

Table 1 - RF radiation compliance information sources.
Table 2 - Some people with ideas about RFR compliance.
Harold Hallikainen is president of Hallikainen and Friends, a manufacturer of transmitter control and telemetry systems. He also teaches electronics at Cuesta College, San Luis Obispo. He can be reached at 805 541 0200. He can also be reached on internet at harold@hallikainen.com .