Synchronous phase-reset FM carrier recording for reference bursts

In general, since the bandwidth of the video signal reproduced by home video cassette tape recorders (VCRs) is narrow below 2 MHz the burst signal cannot be directly recorded in the same way as the processing in the direct-FM recording VTR for broadcasting stations. But the NTSC signal whose chrominance signal is recorded by down-converted AM recording, can be reproduced by means of the double heterodyne system. Since in current VCRs the accuracy of the ordinary sync edge detection is no less than 50 ns (peak-to-peak value), supposing the SNR of the reproduced video signal is 40 dB (Vpp/Vrms), it is difficult to increase the accuracy to less than 30 ns even if using cancellation techniques for the noise superposed on the sync pulse's leading edge by 1 H delay line.<>