Thursday, August 07, 2008

George Campbell Filters!

George Ashley Campbell developed the first electrical wave filter in May of 1917. I cannot begin to explain how important this was to radio. Actually I can. That's why we're here. Before Campbell nobody filtered much other than water and moonshine.

He actually has 2 separate patents on the electric wave filter. He invented the principle and the first practical application of the following:
1. The low‑pass filter
2. The high‑pass filter
3. The band‑pass filter

These were rudimentary, they consisted of simple inductors and capacitors. That first one is now called a "ladder filter." His 2nd patent was more about it's application to the filtration in telephone amplifiers. He'd actually ben using them for years by the time he bothered to patent them. It was his employers at the American Telephone and Telegraph Company that realized this might be important. He'd go on to have a 40 year career in radio engineering.

George graduated from MIT in 1891, and went on in 1893 to get a master’s degree from Harvard University. He went to work for the American Telephone and Telegraph in 1897. American Telephone and Telegraph of course went on to be known as AT&T. More here.

He has been multiply awarded for thsi and other accomplishments in radio engineering. In 1936, the Institute of Radio Engineers awarded him its Medal of Honor. The American Institute of Electrical Engineers awarded him the Edison Medal. He retired from AT&T in 1935 and died in November 1954.