CRV59-AAE Military Iconoscope Camera restoration

[old_tv_nut]

Originally Posted by dtvmcdonald

One astounding tidbit. Looking at the severe noise (the S/N of a sunlit scene
is like 2:1) I noticed something and measured the frequency response. That's the frequency response looking at the width and shape of a full dark-to-light sharp edge or light-to-dark or stripe test patterns. The 3dB down point.

Its 8 MHz. That's eight megahertz. Eight, 8, e i g h t. And it shows on the high end
Ikegami monitor I'm using. Why would they make such a thing when it was supposed
to feed a transmitter that surely not that wide, nor displays that wide either.

It does demonstrate how sharp iconoscopes can be, such as the talking one in Japan :-)

Is the horizontal scan rate 15750? If it's slower, the bandwidth will be less by the same ratio even though the horizontal resolution is high.

[dtvmcdonald]

Originally Posted by old_tv_nut

Is the horizontal scan rate 15750? If it's slower, the bandwidth will be less by the same ratio even though the horizontal resolution is high.

"

Yes, its ~15750 Hz and ~60Hz, locked together, not locked to line.
Put another way, its 262+-1 @ 60p, the latter not locked to power line (since
all the power lines are DC).

But that's immaterial for my main measurement, which actually measured
the rise and fall times of sharp edges in an image. The ringing frequency of the noise agrees.

[dtvmcdonald]

Originally Posted by Electronic M

Given it's a WWII guidance camera and that the military had a lot of leeway on how it used RF during the war it's possible the engineers foresaw the possibility of having a channel wider than 6MHz and higher scan rates for increased resolution for some special application and gave the video circuits enough bandwidth that one could swap the transmitter and tweak the scan to achieve that easily.

The lower the horizontal scan rate the higher, not lower , the resolution in pixels. In any case, I found a statement of 4.5 Mhz bandwidth for that system, and double sideband AM, black at 100% up modulation, but it didn't say whether the 4.5 Mhz was the baseband or the DB channel width. Somebody with a transmitter .... or the manuals ... should know. But nobody has manuals.

[dtvmcdonald]

I've found that trying to run at NTSC rates rather than 14kHz and 40Hz
(progressive) was what was causing big problems with the shading corrections.

Adjusting some cap values and the width coil value, plus adding a small vertical linear correction directly to the output stage fixed that. It now makes a fairly good picture,
still with sone shading problems even if direct sunlight scenes.

It was not drifted component values.

[old_tv_nut]

Originally Posted by dtvmcdonald

I've found that trying to run at NTSC rates rather than 14kHz and 40Hz
(progressive) was what was causing big problems with the shading corrections.

Adjusting some cap values and the width coil value, plus adding a small vertical linear correction directly to the output stage fixed that. It now makes a fairly good picture,
still with sone shading problems even if direct sunlight scenes.

It was not drifted component values.

Nice!

Pictures???

[dtvmcdonald]

The quality in photos has not changed much. Its more visible direct, because you can see the high frequency noise better.
Photos need more than one field exposure, which averages it out.

[old_tv_nut]

Originally Posted by dtvmcdonald

The quality in photos has not changed much. Its more visible direct, because you can see the high frequency noise better.
Photos need more than one field exposure, which averages it out.

Got it. Was wondering if a shading improvement was visible.

[dtvmcdonald]

Originally Posted by old_tv_nut

Got it. Was wondering if a shading improvement was visible.

Not for that scene in broad saylight.
I'm still working on the white stripe near the left edge. This is caused by
ringing in the horizontal deflection pulse used for shading. I was never able to get completely rid of it at 15750 Hz.