Darius new standard converter for 405 TV

[ppppenguin]

It does not matter whether the interpolator works at the input or output. That is only a matter of which way is most convenient. Traditional 625>405 converters do interpolation before time re-distribution. The lines coming out of the interp are still 64us long but only approx 2 out of 3 are written into the circuit that stretches each line from 64us to 99us. A frame store design can be arranged to have more than 1 simultaneous output from the framestore. These are used to feed the interpolator. This sort of design is more flexible if you are trying to do many different conversions.

If only 2 lines contribute to each output line then it's only a 2 line interpolator. Hence you have a 2 line interpolator.

Measuring vertical frequency response is not so easy. You need a vertical frequency sweep with low frequency at the top of the screen and high frequencies at the bottom. Or vice versa. The wave shape must be sinusoidal. Any other wave shape will give large measurements errors.

This sort of sweep can show the effects of interlace and also sweep right through the Nyquist limit which is set by the number of lines. The results of such a sweep can easily be viewed on a 'scope locked to V sync.

A 2 line interpolator will show a gently falling vertical frequency response. The response of a 3 (or more) line interp can be varied by changing the shape of the interpolation function. The theoretical ideal is a sharp cut off but this needs a very large number of lines and will give visible "edgy" artifacts.

[oldeurope]

Good morning,

thanks for your answer Jeffrey. So I have a traditional converter.

The main difference in the drawings from Malcolm and me is:

Malcolm stretches the first line non interpolated and the
second and third are interpolated and stretched.

I am interpolating all lines with 1/3 :2/3 ratio
and from this result I stretch two lines of three in the
right moment.
I think this is a bit more expense.

But I think Malcom made his drawing easyer than it is !?

I can see no vertical resolution loss in my picture.
Vertical aliasing takes place over 400 lines
and you can't get more in a 405 picture.

I made some interesting screenshots for you.

In this test pattern you can see the V and H resolution.

The pics are made from my 405 monitor to show the full resolution.
The converter is the MK III because it has a jumper to switch off
the interpolator.
Two pics are made with flash (closed with my finger) to catch one
frame.
There is some aliasing caused by the computer too.
Please note the missing line without interpolation

Kind regards
Darius

[peter_scott]

Hi Darius,

From Jeffrey's description and your illustration each of your output lines takes weighted information from 2 input lines. Thus 2 line interpolation.

Once I get my playroom up and running again after our building work I will have a go.

Thanks and kind regards,

Peter.

[oldeurope]

Hi Peter,
I made some experiments with the values in the interpolator.
I think I don't understand it completely. It is very complex.
Maybe you will find out how to calculate the values.

Hi Jeffrey,
not only a bad interpolation generates edges in diagonal
lines. This is caused by aliasing too! I did not know this before.

In the new schematic attached, I made new anti aliasing filters;
One filter is added in pos. l-m-4
With PAL and NTSC input the picture looks very good!

Kind regards
Darius

[oldeurope]

Good evening,
here is the update of the schematic.
Now the V- sync (iii) in the Keen- book is generated.

Kind regards
Darius

[Sean Williams]

I also want to try to build one of these - so any support here would be very useful.... Must get the modulator finished fiirst though

Cheers
Sean

[oldeurope]

Good morning,

a new update ( v-sync sep.) comes up soon.

At the moment I am drawing new schematics for the MK III and I am
making an english description for it. Peter Scott is so kind and translates
it from german- english to oxford- english.
I hope this will be finished in the next few month.

Kind regards
Darius

[Sean Williams]

Hi Darius,

I am now very interested in building one of these converters - I wonder, do you have a parts list assembled?

Cheers
Sean

[oldeurope]

Hi,
a parts list? No, makes no sense to me, time waste.
I made a new sync sep and a V sync generated from the mains
in the "no signal at the input" mode.
The updates are comeing up next week.

Kind regards
Darius

[Sean Williams]

Hi Darius,

Ok, no problem, However, I am having problems identifying some of the IC part numbers....

Thanks
Sean

[oldeurope]

http://www.datasheetcatalog.com/

Hi, on this (free)website you find infos on semiconductors and IC's.
I was not able to find anything about the MSM7403 delay ccd.
I think the Sony CXL 5508 and 5506 are the better choise but
they are only in smd available.
Maybe you find other usable ccd's.

Kind regards
Darius

[oldeurope]

Good evening,
sorry for the delay, here are the new updates.
The LM1881 is replaced by a discrete sync separator.Q38 39 pos.8m
One disadvantage of the IC is it does not work with non standard
V-syncs. It waits for the first serration pulse to trigger the V-output.
This causes a delay if the V sync has no equializing pulses or serration
pulses.
To get a V sync an integrator 15m is used and a comperator LM393 16n
forms the V- pulse.
In the no signal at the input mode, it generates a V- sync from the mains
frequency in pos.18n it gets 6VAC from the mains transformer of the power
supply.

The modulator update with the blocking to emitter causes an emphasis
in the video. To compensate this, a 82pF cap is added 4b.
To get the same frequency response in the video amp and the modulator
a 220 Ohms 220pF is used in the emitter of Q31 6/7a. In the modulator
it is 100pF 470 Ohms. So the RxC is the same.

Kind regards
Darius

Kind regards
Darius