03-10-2016, 12:06 PM
(03-10-2016, 07:42 AM)ppppenguin Wrote: Whether you choose 1/10 of a wavelength or any other number is a bit arbitrary. Ultimately it depends on how much error you're prepared to ignore by treating a transmission line as lumped C and L. At 1/4 wavelength the errors are likely to be severe. At 1/10 it may or may not matter depending on your requirements.
(03-10-2016, 07:43 AM)pwdrive Wrote: The 1/10th wavelength I originally quoted was a figure I plucked off the web from a "professional" page, other "professional" pages quote 1/8th wavelength, my own interest in transmission lines leans towards RF/Antennas etc and the effects of mismatching.
Yes, there's certainly a range out there. But I was particularly interested in hearing Gryphon's preference (and reasoning for that preference), as his earlier post hinted that he might have particular insight into the matter:
(02-10-2016, 09:19 PM)Gryphon Wrote: Someone upthread said that you need to start thinking transmission line theory if the line length approaches one-tenth of a wavelength (not the figure I would use myself, but never mind).
(my emphasis)
(03-10-2016, 07:42 AM)ppppenguin Wrote: For analogue video, connections outside a piece of kit are always properly terminated at both ends. This keeps the amplitude correct as well as eliminating visible ghosting and frequency response errors.
A nice "visual" dem that I liked doing: with appropriate lengths of cables, it's very easy to knock out the colour subcarrier. Obviously less justifiable to spend time on that in these post-PAL days, but still something I try to do when I can, as it helps consolidate the basic transmission line and loading effects theory that we have to labour because new many recruits seem to struggle with these concepts, despite their time at university.
