Abstract
Statement of Problem
The problem that this thesis plans to address is the conversion of vintage Amplitude Modulated (AM) commercial broadcast transmitters to be used in current radio Amateur service. By design AM radio broadcast stations employ transmitting units on fixed frequencies in what is referred to as the AM broadcast band covering 550 KHz to 1.750 MHz in the United States. These stations are licensed by The Federal Communications Commission (FCC) to operate on one assigned frequency within the limits of the frequencies noted. Licensing also requires that station owners verify that their transmitting stations will stay within the bounds and limits of their assigned licensure. Commercial stations are licensed for continuous service in a for-profit business model, while Amateur radio is designated by the FCC as a means for licensed individuals to communicate between one another on certain allocated frequency bands.
From the early era of their invention in the early 20th century until technological advancements allowed for cost effective transistors in the 21st century, most of these transmitters were designed based on vacuum tube technology. Some commercial AM broadcast stations still rely on vacuum tube technology out of economic necessity as the capital investment to upgrade to solid state equipment exceeds the revenue capability of the upgraded equipment. The increased economic benefit of solid-state transmitters in the past decade coupled with the scarcity of transmitting vacuum tubes has driven the industry towards upgrades at a much faster rate. Hence the marketplace has sent many vacuum tube transmitter systems into the surplus markets or to Electronic-Waste (E-Waste) recycler with little to no second-hand value. And to that end an enterprising segment of the Amateur Radio Operator Community have purchased these units on the surplus market to keep this nostalgic hardware on the air to see a continued existence as useful communications equipment.
This thesis addresses the conversion of commercial AM broadcast transmitters through the design of frequency control systems, audio interface systems, and harnessing required to ensure FCC compliance under Amateur operating guidelines. For the purposes of this writing, the terms Amateur and Ham radio will be used interchangeably.
Sources of Data
Amateur radio periodicals, such as QST, constitute the bulk of primary source material. Additional primary sources include books written during the periods examined; journals; general electronics hobby magazines reflecting the technology of a specific period; government documents; minutes of the American Radio Relay League (ARRL); interviews; and oral histories taken from Amateur radio operators. Secondary sources include photographic documents of equipment associated with the Amateur radio service, internet special interest newsgroups associated with Amateur radio history, and published accounts of Amateur radio accomplishments by current authors.