H
Hans Summers
Guest
I'm reposting this message here after advice on rec.radio.amateur.homebrew
that video gurus congregated here...
I am having a minor problem with the display on my spectrum analyser Mk2
project, see
http://www.hanssummers.com/electronics/equipment/spectrumanalyser2/index.htm
.. The display for this analyser is an 4.5-inch ex-TV tube. I successfully
dismantled that TV and rebuilt the necessary drivers etc as a miniature
monitor having TTL-level video and composite sync inputs.
Naturally the type of display this tube is now being subjected to is very
different to a TV picture. There seem to be some problems with the video
drive circuits, see pictures at the bottom of the above web page. The
graticule fades out in the top eighth of the screen. Also see the "noise
floor" photo which shows significant horizontal "bulge".
Also there is a resolution problem - one spectrum analyser sweep consists of
640 measurements, and I have a complicated interpolation circuit which
"joins the dots" i.e. draws lines between the individual measurements, and
also reduces the horizontal resolution to 320 pixels which I hoped would be
displayable on the monitor. Problem is I can only get 160 horizontal pixels
to display reliably - at 320 pixels a vertical line is very faint or
invisible (depending on how much white there was in the preceeding
microsecond or so's worth of scan line.
The circuit diagram is also on that page
(http://www.hanssummers.com/electronics/equipment/spectrumanalyser2/circuitm
..pdf). I'm no TV expert. Can anyone suggest what modifications should be
made to the video driver circuit to correct these problems?
Hans G0UPL
http://www.HansSummers.com
that video gurus congregated here...
I am having a minor problem with the display on my spectrum analyser Mk2
project, see
http://www.hanssummers.com/electronics/equipment/spectrumanalyser2/index.htm
.. The display for this analyser is an 4.5-inch ex-TV tube. I successfully
dismantled that TV and rebuilt the necessary drivers etc as a miniature
monitor having TTL-level video and composite sync inputs.
Naturally the type of display this tube is now being subjected to is very
different to a TV picture. There seem to be some problems with the video
drive circuits, see pictures at the bottom of the above web page. The
graticule fades out in the top eighth of the screen. Also see the "noise
floor" photo which shows significant horizontal "bulge".
Also there is a resolution problem - one spectrum analyser sweep consists of
640 measurements, and I have a complicated interpolation circuit which
"joins the dots" i.e. draws lines between the individual measurements, and
also reduces the horizontal resolution to 320 pixels which I hoped would be
displayable on the monitor. Problem is I can only get 160 horizontal pixels
to display reliably - at 320 pixels a vertical line is very faint or
invisible (depending on how much white there was in the preceeding
microsecond or so's worth of scan line.
The circuit diagram is also on that page
(http://www.hanssummers.com/electronics/equipment/spectrumanalyser2/circuitm
..pdf). I'm no TV expert. Can anyone suggest what modifications should be
made to the video driver circuit to correct these problems?
Hans G0UPL
http://www.HansSummers.com