Jacoby Barrera (2019). Broadcasting Journalism. EDTECH. pp. 129–132. ISBN 9781839472893. 9781839472893
John S. Seybold (2005). Introduction to RF Propagation. Wiley. p. 54. ISBN 9780471743682. 9780471743682
Graham A. Jones; David H. Layer; Thomas G. Osenkowsky; Edmund A. Williams (2013). National Association of Broadcasters Engineering Handbook: NAB Engineering Handbook. Taylor & Francis. p. 759. ISBN 9781136034107. 9781136034107
B. Whitfield Griffith (2000). Radio-electronic Transmission Fundamentals. Noble Publishing Corporation. pp. 411–419. ISBN 9781884932137. 9781884932137