Time-Frequency Multiplexing (TFM) of Two NTSC Color TV Signals - Simulation Results

It has been known for some time that frequency-division multiplexing (FDM) of two 4.2-MHz National Television System Committee (NTSC) color television signals onto one microwave radio channel is often unsatisfactory because nonlinear distortion causes visible crosstalk between the two pictures. Also, we suspected that 2:1 time compression followed by time multiplexing would lead to problems because of the color carrier (initially 3.58 MHz) being transmitted at 7.16 MHz, where it is much more susceptible to degradations such as selective fading. However, there are other techniques which show promise of not having such problems. Here we propose time-frequency multiplexing (TFM), which involves sending two successive scan lines (or fields) from one picture during one line (or field) interval, followed by two lines (fields) from the other picture in the remaining time interval. The two successive lines (fields) 643 from one picture would be transmitted simultaneously via frequencydivision multiplexing. Multiplexing in this manner avoids crosstalk from one picture into the other which would otherwise be caused by nonlinearities in the transmission if simple FDM were used. We hypothesized that nonlinearity induced crosstalk between successive lines (fields) in the same picture will be much less serious because of their high similarity and the fact that the ghost of a picture overlayed upon itself is practically invisible. With these methods the two incoming pictures would have to be in phase synchronism.