View Full Version : Color TV Chroma Bandpass Alignment


Penthode
05-14-2016, 06:22 PM
I have completed the RF and IF alignment of my CTC5 Deluxe. Tackling the chroma alignment has been a bit of a challenge in as much as the CTC5 service notes requires a 0-5MHz video sweep with markers.

The CTC5 Deluxe I believe is unique in the realm of early RCA color TV design because it uses an asymmetrical chroma bandpass amplifier (2.5MHz to 4.1MHz) for both chroma demodulation axes. The CTC2 had different bandpasses for each axis and the CTC5 Super and CTC7 upward appeared to have equal double sideband (3.0MHz to 4.1MHz) for both axes.

The original RCA Service Data required a 0 - 5MHz sweep generator feeding a RCA Multimarker WG-295A and an RF Modulator fed by the multimarker with a channel 4 video carrier from an RF signal generator. The original RCA multimarker and modulator are all but non-existent and I am planning to use my HP8601a sweep generator with HP8600a marker generator to replace the RCA suggested equipment.

Note that the uniqueness of the RCA CTC5 Deluxe design is curious as it provides extra chroma resolution at the expense of introducing quadrature crosstalk in demodulation. I recall many years ago a discussion of this in the RCA Review although I cannot recall the context of the discussion. Early NTSC color receivers suffered to a degree by the low color resolution which meant that finer detail color elements which should otherwise be resolvable could not be reproduced. Later PAL development allowed wider chroma bandwidth because the quadrature crosstalk would be effectively cancelled by the alternating R-Y axis.