Austin transformer

Etymology

It is named after its inventor, Arthur O. Austin.[https://www.austin-insulators.com/radio/xfmr-hist.html Transformer Design History], retrieved 2024 Sep 24

Background

AM radio stations that broadcast in the medium frequency (MF) and low frequency (LF) bands typically use a type of antenna called a base-fed mast radiator. This is a tall radio mast in which the steel mast structure itself is energized and serves as the antenna. The mast is mounted on a ceramic insulator to isolate it from the ground and the feedline from the transmitter is bolted to it. Typically the mast will have a radio frequency AC potential of several thousand volts on it with respect to ground during operation.

Aviation regulations require that radio towers have aircraft warning lights along their length, so the tower will be visible to aircraft at night.{{cite book

Use and mechanism

The Austin transformer 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 is formed of two interlocking rings: one with the transformer core and primary windings, much like a conventional toroidal transformer and the other with the secondary windings. The secondary is wound like in a typical toroidal transformer but with a very large diameter to reduce interwinding capacitance and undesired capacitive coupling of RF energy. The power from primary to secondary is transferred by inductive coupling. It is used for providing power to the aircraft warning lights and other devices on a mast radiator antenna insulated from ground. In the Austin transformer the primary and secondary windings are separated by a large air gap, so that the high voltage and AM RF energy on the mast cannot couple into the low voltage lighting supply wiring, causing safety hazards and electromagnetic compatibility issues. |chapter-url=https://books.google.com/books?id=m5DIroWLw2EC&pg=PA367 |edition=2nd |chapter=Practical operation of the vertical antenna }} It consists of a ring-shaped toroidal iron core with the primary winding wrapped around it, mounted on a bracket from the mast's concrete base, connected to the lighting power source.{{cite report | access-date = 7 April 2020}} The secondary winding which provides power to the mast lights is a ring-shaped coil which circles the toroidal core through the center, 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. The wide gap of several centimeters between the coils also ensures that there is minimal interwinding capacitance, to prevent RF voltage being induced in the supply wiring by capacitive coupling. A spark gap is often located nearby with a gap smaller than the gap between the rings, to prevent damage to the transformer and transmitting equipment in the case of a lightning strike.

References

References

1. Mehla, Ishwar Singh. (2018). "AM Radio Tower Antennas". Notion Press.