A survey of tuner designs for multi-channel television reception

摘要

Channel availability for national television systems is stated and an historical outline given of design development for multi-charnel reception in the U.S.A. The survey includes those designs of British, American and European origin which the authors have had the opportunity of investigating and for which the paper includes performance data. Chief emphasis is placed on a rotary coil turret design first developed in America, which has proved to be the most flexible and versatile tuner examined. Effects of receiver noise governing first stage design are considered and aerial noise over the spectrum is calculated to decide the minimum required noise factor for each channel when receiver noise becomes equal to aerial noire. The conclusions are that this condition is obtained with a receiver noise factor of 22 db at 40 Mc/s decreasing to 3 db at 220 Mc/s. The importance of these considerations are emphasized for fringe area reception. The immediate problem of enabling existing single channel receivers to operate for muiti. channel reception is discussed. A solution considered to be the most successful is described in which the double superheterodyne system is avoided and installation made possible without a soldering operation; the tuner provides an output at the receiver i.f. and is connected in place of the original r.f. stages. The future requirements for ultra-high frequency multi-channel reception in the United Kingdom are discussed, and tuner designs incorporating lumped and distributed tuning elements are examined.