240i CRT TV?

[90sTV]

Someone was telling me that he had a CRT that was 240i, not 480i. I'm extremely skeptical of this claim, as I've never read anything about such a thing existing, nor does it seem logical to me. Since the broadcast signals were 480i, that would mean that the display would have to somehow throw away half of each field to draw 120 lines followed by another 120 lines.

Is this person just mixing up the vertical dimension with the horizontal dimension, since the vertical lines per picture height figure was variable?

[pandy]

Well it can be or mistake or truth - CRT as fully capable to display 240i maybe even regular TV's with flexible V deflection circuit - you can assume that to keep H frequency same as in TV you need refresh 240i screen twice faster so efficiently such system will be capable to display 100 fields per second.

Sony Watchman FD-210 (and later models) portable TV with special CRT valve have limited vertical resolution but was fully compatible with TV standard.
Also there is special SSTV that may give similar parameters...

In other words 240i is meaningless description for CRT (and video standard per se) and FYI there are interlace patterns than well known 2:1 - sometimes interlace can have 3, 4 or more fields especially when special CRT valves with long persistency are used - i can imagine ultra hires monochromatic military screen where such weird interlace patterns can be useful (some radar tubes was combined in a way: main screen for radar and additional HW overlay in same CRT to display data information with hi res)

[aedipuss]

i wouldn't put much faith in it. as has been discussed before ntsc analog tv was broadcast using 525 lines with 2 passes of the electron gun completing a line for an effective resolution of 262.5p lines with some lost top and bottom to overscan. and tvs were never described as 480i or 240i. the most important parts of analog tv were dot pitch, shape, and persistence.

[90sTV]

i wouldn't put much faith in it. as has been discussed before ntsc analog tv was broadcast using 525 lines with 2 passes of the electron gun completing a line for an effective resolution of 262.5p lines with some lost top and bottom to overscan. and tvs were never described as 480i or 240i. the most important parts of analog tv were dot pitch, shape, and persistence.

But dot pitch is what affected the resolution in the horizontal dimension, correct? I was thinking that vertical resolution was basically the same on all SD televisions. Roughly 480 visible interlaced lines after accounting for overscan.

[manono]

Roughly 480 visible interlaced lines...

But with only 240 of those on the screen at a time, maybe that's what the guy means by that 240i nonsense.

[TreeTops]

240 dots total on a normal television CRT would be a really small picture. A couple of inches square or smaller. I remember really small CRT's on our circuit testing equipment in the 1950's. Maybe that's what the op is talking about.

[lingyi]

It's probably a arcade videogame monitor displaying "262 lines (240 active + 22 blanking) x 60 Hz = 15.7 kHz (many games)"

The quote above is from here:

http://easymamecab.mameworld.info/html/monitor9.php

I just browsed through a few of the pages, but there's lots of info about CRTs. I'm looking forward to reading it all!

[90sTV]

Do smaller CRT TVs tend to have finer dot pitches than larger ones?

[pandy]

Do smaller CRT TVs tend to have finer dot pitches than larger ones?

Some of them yes, some not - generally dot pitch was related to time when CRT was constructed, modern CRT's have significantly smaller dot pitch - modern CRT's are capable to display more than 2048 RGB pixels in line and with particular designs vertical resolution is limited only by shape of spot from electron beam.
Special CRT's (like those with microchannel plates) was capable to produce extremely high resolutions and at the same time flat, no geometrical distortions picture...