Video Amplifier for long distance transmission

Dustin Knudsen

Other Parts Discussed in Thread: OPA454, THS6212

Hello,

I am looking for guidance for TI part numbers to help me with a project. I need to amplify a video signal down a 15 AWG shielded wire, approximately 5 KM. The video signal is a NTSC/PAL composite signal 1 volt P/P, 540 TVL, 768H x 576V. I have estimated the voltage drop along the line to be about 45 volts, so I would assume the signal would need to be boosted by ~50 volts to achieve this. Does anyone have any suggestions or any TI circuit diagrams you can send to lead me in the right direction? I was originally looking at the OPA454 high voltage OpAmp but noticed the slew rate was only rated around 13 volts/us. My signal runs over 100 volts/us slew rate I believe so this wouldn't work. Any help would be greatly appreciated. Thanks.

over 7 years ago

0 kai klaas69 over 7 years ago

Guru 140200 points

Hi Dustin,

you should use transmission line technique and should terminate both ends of cable with the characteristic impedance of transmission line:

en.wikipedia.org/.../Transmission_line

And use a transmission line which provides very low losses. You could insert buffers / repeaters which you power by a remote power supply.

An alternative would be the transmission over an optical fibre.

Kai

0 Ron Michallick over 7 years ago in reply to kai klaas69

TI__Guru**** 174826 points

Hello Dustin,

5 kM of cable sounds expensive to me. You may also need to compensate for high frequency losses. Line of sight RF with a directional antenna would be easier but be sure to follow government rules. Is this a home project?

0 Michael Steffes over 7 years ago in reply to Ron Michallick

Guru 48395 points

This used to come up a lot in security camera applications - there are chip sets out there to do this job where the receivers are lossy cable equalizers with gain ramping up a lot as you go up in frequency. Don't remember the part numbers, but I am sure you can find them - no need to recreate the wheel on this one.

0 Dustin Knudsen over 7 years ago in reply to Michael Steffes

Prodigy 230 points

Thanks Michael, thats what I thought too. Does this seem like a suitable chipset?

https://cdn.anaren.com/product-documents/MSK/Amplifiers/MSK130/MSK130_DataSheet(Rev_f).pdf

Its the only one I could find so far that had appropriate slew rate and high voltage to drive down the line.

0 Dustin Knudsen over 7 years ago in reply to Ron Michallick

Prodigy 230 points

Hey Ronald, I am handcuffed to 5 KM of 15 AWG wire. Its actually a wireline truck running a video camera down a well. The video camera needs to transmit the video data up the 5 KM of wireline to the truck, where it will then be corrected for display.

0 Michael Steffes over 7 years ago in reply to Dustin Knudsen

Guru 48395 points

So Dustin, twisted pair driving is a well known area in both security video and VDSL - no one uses a part like you sent, For DSL twisted line drivers those go over many miles using +/-15V dual CFA type devices like the THS6212 - but that is just an example, not necesarily what you want - I have pinged some security video contacts for ideas,might get a reply - I don't think TI has anything there.

So yes, launching some pretty good swings into the cable helps, but it is really equalizing receiver that this the key to flatten out the lossy cable response.

0 Michael Steffes over 7 years ago in reply to Michael Steffes

Guru 48395 points

So Dustin, I do not believe TI offers parts like these, but if they do - someone chime in - there was quite a series of Cat-5 drivers from Intersil. They did quite a bit of work in this area, with many app notes like this

www.renesas.com/.../an1307.pdf

That was an earlier one, where later there was a whole series of dedicates Cat-5 differential line drivers - I could only find a triple fast one, actually originally Elantec parts - I know they have singles as well - you can ask them,

www.renesas.com/.../el4543.pdf

And then for the equalizing recievers - look at

EL9110, ISL59911, ISL59910, ISL59603

And then there is a lunatic fringe version of all this in something called the Mega-Q Compensation - this is all about peaking the receiver gain as freqeuncy increases to equalize the rolloff described in that first app note.

0 Ron Michallick over 7 years ago in reply to Dustin Knudsen

TI__Guru**** 174826 points

Dustin,

Tell me more about this shielded wire. Is this a coaxial cable? Wire in center then (moving out) insulator, metal braided shield, and outer insulator?

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Video Amplifier for long distance transmission