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The discussion of the 1930's American transmission channel has raised a few questions in my mind pertaining to television receiver design. It may be interesting to compare RCA's development with it's sister Marconi/EMI partner.
The development of the 405 line standard is interesting. It was early and a somewhat premature standard which persisted for nearly five decades. Positive modulation, no equalizing pulses and video delivered AM full double sideband on the original Alexandra Palace transmission channel 1 until 1956. Subequent VHF channels added with the post WWII UK expansion on channel 2 upwards was vestigial sideband. I restored a Baird T5 (1936), an HMV 900 (1937) and a Baird T-18 (1938) and each did not have a tuner. I recall the T5 and 900 used superheterodyne frequency conversion in the video channel. Th Baird T-18 was a straight TRF video receiver with the video rf amplifier tuned to channel 1. (UK prewar receivers were later provided with heterodyne converter adaptors so the prewar sets could receiver other than channel 1.
I also previously restored post war HMV, Bush and Pye receivers. These video receivers were designed for vestigial sideband reception of all the postwar channels. It is important to note that a vestigial sideband designed receiver can properly demodulate double sideband signals without distortion but the opposite is not true. So prewar receivers had to have the video IF response modified to provide a nyquist slope for proper demodulation.
This leads me to the American development of receivers in the late 30's. It must have been noticed early on when designing sets in the effort to reduce the tube count and save money by narrowing the receiver amplifier bandwidth that when tuned to one side with the video carrier on the response sliope that the video baseband response would be extended. In other words the benefits of receiver design cost savings came first even before the consideration of RF spectrum savings.
This leads me to wonder if the frequecy response depicted in figure 2 was an attempt of the earliest implementation of the nyquist slope detection prior to VSB transmission?
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