page_title: Mast radiator
section_title: Aircraft warning lights
hierarchical_section_title: Mast radiator / Ancillary equipment / Aircraft warning lights
caption_attribution_description: English: [text from https://www.flickr.com/photos/infrastructure/39714749543/in/album-72157677570210968/] Along the catwalk to the towers of WMCA/570 and WNYC/820, two New York AM stations that once fought over exclusive rights to the 570 dial position (they shared time and then WNYC lost and had to become a daytimer farther up the dial), and are now diplexed on three 326-foot Truscon towers standing in an impounded flood-control pond alongside the Hackensack River along the Belleville Pike in Kearny, New Jersey, just off the East spur of the New Jersey Turnpike. The site was still sort-of-solid swamp ground when WMCA built the facility in 1940. WNYC moved there in 1993, also becoming a full-time station, with 10kw by day and 1kw by night. WMCA has been full-time with 5kw for the duration.
context_page_description: A mast radiator is a radio mast or tower in which the metal structure itself is energized and functions as an antenna. This design, first used widely in the 1930s, is commonly used for transmitting antennas operating at low frequencies, in the LF and MF bands, in particular those used for AM radio broadcasting stations. The conductive steel mast is electrically connected to the transmitter. Its base is usually mounted on a nonconductive support to insulate it from the ground. A mast radiator is a form of monopole antenna.
context_section_description: Antenna masts are tall enough that they can be a hazard to aircraft.    Aviation regulations require masts to be painted in alternating strips of international orange and white paint, and have aircraft warning lights along their length, to make them more visible to aircraft.  Regulations require flashing lights at the top, and (depending on height) at several points along the length of the tower.  The high radio frequency voltage on the mast poses a problem for powering the warning lights: the power cable which runs down the mast from the lights to connect to the mains power line is at the high RF potential of the mast.   Without protective equipment it would conduct radio frequency (RF) current to the AC power wiring ground, short-circuiting the mast.  To prevent this a protective isolator is installed in the lighting power cable at the base of the mast which blocks the RF current while letting the low frequency 50 or 60 hertz AC power pass through up the mast.  Several types of isolator devices have been used:  
  Austin transformer - this is a specialized type of isolation transformer made specifically for this use, in which the primary and secondary windings of the transformer are separated by an air gap, wide enough so the high voltage on the antenna cannot jump across.  It consists of a ring-shaped toroidal iron core with the primary winding wrapped around it, connected to the lighting power source.  The secondary winding which provides power to the mast lights is a ring-shaped coil that threads through the toroidal core like two links in a chain, with an air gap between the two. The magnetic field created by the primary winding induces current in the secondary winding without the necessity of a direct connection between them.
  Choke - this consists of an inductor, a coil of fine wire wound around a cylindrical form.  The impedance (resistance to AC current) of an inductor increases with the frequency of the current.  The isolation choke is a low pass filter, it is constructed to have a high impedance at radio frequencies which prevents the RF current from passing through, but negligible impedance at the lower 50/60 hertz mains frequency, so the AC power can pass through to the lights.   A choke is inserted in each of the 3 lines (hot, neutral, safety ground) that make up the power cable.  The low voltage end of each choke is bypassed through a capacitor to ground, so high voltage induced in the low voltage end by capacitive coupling through the interwinding capacitance of the choke is conducted to ground.
  Parallel resonant circuit (trap) - this consists of an inductor and capacitor connected in parallel in the power line.  The values of the inductance and capacitance are chosen so the circuit's resonant frequency is the operating frequency of the antenna.  A parallel resonant circuit has a very high impedance (thousands of ohms) at its resonant frequency, so it blocks the RF current, but low impedance at all other frequencies, allowing the AC lighting power through.  This circuit only blocks the specific frequency it is tuned to, so if the frequency of the radio transmitter is changed, the trap must be adjusted.
caption: Austin transformer at the base of the WMCA and WNYC transmitter tower in Kearny, New Jersey
exif: {"Image PhotometricInterpretation": "2", "Image Make": "Canon", "Image Model": "Canon EOS 5D", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS6 (Macintosh)", "Image DateTime": "2019:01:09 11:06:14", "Image ExifOffset": "222", "EXIF ExposureTime": "1/320", "EXIF FNumber": "9", "EXIF ExposureProgram": "Program Normal", "EXIF ISOSpeedRatings": "100", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2014:11:10 10:03:09", "EXIF DateTimeDigitized": "2014:11:10 10:03:09", "EXIF ComponentsConfiguration": "YCbCr", "EXIF ShutterSpeedValue": "67/8", "EXIF ApertureValue": "51/8", "EXIF ExposureBiasValue": "-1/3", "EXIF MaxApertureValue": "4", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "85", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "2907", "EXIF ExifImageLength": "3483", "EXIF FocalPlaneXResolution": "83347/27", "EXIF FocalPlaneYResolution": "188569/61", "EXIF FocalPlaneResolutionUnit": "2", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Manual", "EXIF SceneCaptureType": "Standard"}