Video cable length compensator

Video cable length compensator: ftp://panteltje.com/pub/video_cable_lenght_compensator.gif

Actually the real one has a diode clamp at the input. But very cheap, compensate the capacitance of 20 meter audio cable of about 100 pF / meter of unknown impedance, works great. The green lines are amplitude and phase at the end of the cable. The blue lines are the corrected amplitude and phase at the 75 Ohm load.

It is possible to add more correction RC networks. I have a peaking a bit, looks better. Adjust trimmer on leading edge of H sync for minimum under - and overshoot, just like you adjust a scope probe.

Reply to
Jan Panteltje
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100 pF / meter of

Not exactly new :-)

What would make this really juicy would be an auto adjusting circuit. Either compare the color burst against sync hoping the color burst was sent conforming to standard, or do an automatic TDR to gauge the cable length. Now that would be fancy.

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Regards, Joerg

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Reply to
Joerg

100 pF / meter of

Nor an accurate rendition. 75 Ohms and "cable capacitance" is not an adequate representation of coax.

...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

On a sunny day (Wed, 07 Oct 2009 12:18:32 -0700) it happened Jim Thompson wrote in :

100 pF / meter of

It is not coax!

Bull. the function is to get the right video on my screen. But feel free to publish your first circuit here.

Dreamers.

Reply to
Jan Panteltje

100 pF / meter of

Hey, that was meant as a joke ...

On mine I had a simple peaker. One transistor, about 300ohms in the collector and the emitter, then emitter peaked with a series RC in parallel to this 300ohms, emitter follower to 75ohm load. I don't think that needs publishing anymore in this day and age :-)

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Regards, Joerg

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Reply to
Joerg

100 pF / meter of
--
If it has a center conductor surrounded by a dielectric which is
surrounded in turn by a tubular shield, and they all share the same axis
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Reply to
John Fields

On a sunny day (Wed, 07 Oct 2009 12:38:50 -0700) it happened Joerg wrote in :

Too bad, because you need a base gain of at least 2, and your example has a gain of 1. Dreamers.

You need the gain of 2 so you have the same voltage at the output as at the input. That little cable driver I published is actually a very good one. I think you will have a hell of a job coming up with a better discrete one, even in spice.

There is an old saying, in Holland (= The Netherlands for you Americanions). 'De beste stuurlui staan aan wal' Freely translated: 'The best skippers are always on shore'. (Where they comment on the real stuff without getting wet).

Q
Reply to
Jan Panteltje

input.

What for if you drive the load directly without source termination?

As I said before, nearly all this stuff was made for employers and clients. So I did get wet but cannot possibly just copy their schematics onto the web. I am doing this kind of stuff for well over 20 years now. Mostly not 5MHz limited though but up to 20MHz, sometimes 50MHz (ultrasound). The cables to be driven or received from are whatever we can get in the desired form factor, not much choice there.

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Regards, Joerg

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Reply to
Joerg

I think he's driving cat5 cable. Mike

Reply to
amdx

Receiving. It's usually best to put the equalizer at that end so you can see the results right then and there.

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Regards, Joerg

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Reply to
Joerg

Wow. Jan seems to be starting to channel Phil A. Can autism, coprolabia, and exclamation points be far off?

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

On a sunny day (Wed, 07 Oct 2009 14:44:33 -0500) it happened John Fields wrote in :

about 100 pF / meter of

Maybe, but this cable is not like that :-)

Reply to
Jan Panteltje

On a sunny day (Wed, 7 Oct 2009 14:57:08 -0500) it happened "amdx" wrote in :

No no, it is one of those ancient 4 core audio cables. There is some screening, and it is sort of wrapped around each core, but I think the term is 'partially screened individual cores' or something. Probably mainly to prevent crosstalk between left and right, but not like 'diode cable' where you have to different screened conductors.

Screening is not really good, or complete, I have used the same cable for I2C remote use, I2C low speed that is, and you could pick up the data on the radio.... In audio it is normally used for line level stuff, not for mike level stuff.

Reply to
Jan Panteltje

On a sunny day (Wed, 07 Oct 2009 12:55:55 -0700) it happened Joerg wrote in :

input.

Asking for refections is not what I had in mind.

Also your circuit 'emitter follower' is not in the feedback loop. the voltage drop across the emitter is dependent on the current, so it introduces distortion. I did not say you never designed one.. just that is sucks.

Q

As to that other poster, Jim Tombson, he is just a coward. He kill files anyone who can really give him decent reply to his sick republican ideas. Republicans are cowards who bomb little children from planes to get a higher oil price for themselves and democrats. So stupid as well. They are, basically, anti-Americans. they do seem to breed a lot though, although the pollution they create will probably end that too.

E
Reply to
Jan Panteltje

Excuse me, but it's the bad skippers that get wet.

John

Reply to
John Larkin

On a sunny day (Wed, 07 Oct 2009 16:39:59 -0400) it happened Phil Hobbs wrote in :

You seem to know shit about that stuff too :-)

Yea, sure. You need one.

See, I can do it too :-)

Reply to
Jan Panteltje

input.

We always terminate the receiving end properly so there are no reflections.

My clients were of different opinion, else it wouldn't have gone into production.

[...]
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Reply to
Joerg

Kinda like Obama's doing now?

Thanks, Rich

Reply to
Richard the Dreaded Libertaria

On a sunny day (Wed, 07 Oct 2009 14:16:29 -0700) it happened Richard the Dreaded Libertarian wrote in :

Rich, there are good republicans too, like you perhaps ;-) Obamama is, like many a president, a puppet in the game of the powerful multinationals. But he wants the Americans to have a btter life. The Son of a Bush before him just wanted to channel $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$(1) to his Saudi masters, who BTW also own much of the US weapon industry, so he is anti-American for sure. See what happened to your finances while he was 'boss'. And his paranoia 'Osama under your bed' stuff, now that is really sick. I think a lot of republicans who see they are on the wrong horse will switch to democratic, Even that Californian warlord now wants to play with the democrats on health care.

(1) Usenet really does not have a maximum line length, so I could have written something like $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ make 518, but in this case you need scientific notion I think:-) Somebody I know told me: Buy gold.

Reply to
Jan Panteltje

On a sunny day (Wed, 07 Oct 2009 14:13:21 -0700) it happened Joerg wrote in :

input.

Well, there is a lot of stuff in production that should not be.

Reply to
Jan Panteltje

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