How to Split NTSC Composite Video signal ?

[SingSing]

I have a DVD recorder, that only has an NTSC tuner.
In order to record DTV program, I need to split the my DTV tuner going to the TV. I used those one RCA to two RCA Y connectors, and managed to duplicate the audio/video signal to both the recorder and the TV.

The problem is that all the video look red and dull now. I figure that is caused by mismatch.



I look up NTSC composite specification, and figure I can use two AC coupled low noise op-amps with 10MHz BW and duplicate the signal to fix the issue.

Before picking up the soldering iron, I would like to find out will a resistive splitter works? and what is the input impedance of NTSC signal? and what is the resistors value ?

Note: To split a 50 OHM RF signal, a Y connection of three 18 ohm resistors are commonly used.

Note: I figure the audio signal impedance is normally about 47 KOHm, so those Y RCA connector will work.

[olyteddy]

Use two unity gain op-amp buffers with a single 75 ohm termination on the input of one of them. You can either cascade them or parallel the inputs just as long as you only have one 75 ohm termination on the video. Your typical Video Distribution Amp puts the inputs in Parallel.

[SingSing]

75 ohm is TV's RF impedance! not applicable to composite video.

[jagabo]

Might be easier to just buy a video distribution amp.

[olyteddy]

75 ohm is TV's RF impedance! not applicable to composite video.

It's both. Believe me. See page 2 of: http://www.jaycar.com.au/images_uploaded/impmatch.pdf

[sanlyn]

Might be easier to just buy a video distribution amp.

CE Labs makes several excellent a/v distribution amps. I've been using their s-video and composite models for years with excellent performance. They also make component versions I've seen in action. There are competitors, but they're either too pricey or too mediocre (the Radio Shack versions are complete junk). The biggest problem with these products is possible overload from the amplification, but you can cure that by using longer connecting cables -- most amps of this type were designed for fairly long connections throughout a house. Building your own op-amps is one solution, but the components and corrective circuitry in commercial distribution amps is probably superior.

[olyteddy]

Might be easier to just buy a video distribution amp.

Yeah, but with a $.79 op amp, $.50 worth of resistors and a couple of 9 Volt batteries why not build one...

[turk690]

What OP amp is that $0.79 item??

[jagabo]

something like this maybe:
http://www.goldmine-elec-products.co...038&variation=
4 MHz may not be enough bandwidth though.

[turk690]

There are dedicated video op-amps from such manufacturers as National Semiconductor and Maxim but they cost more than $0.79 each and the LF351 is NOT one of them. The LF351, and others of the same ilk (TL072, LF347, etc.) are bifet-input op-amps normally used for audio.

[jagabo]

He's only dealing with 3.58 MHz composite video.

[olyteddy]

There are dedicated video op-amps from such manufacturers as National Semiconductor and Maxim but they cost more than $0.79 each and the LF351 is NOT one of them. The LF351, and others of the same ilk (TL072, LF347, etc.) are bifet-input op-amps normally used for audio.

Here's one: http://www.jameco.com/webapp/wcs/sto...oductId=23608& 15MHz nominal bandwidth...

[edDV]

Why not this as suggested?

http://www.google.com/products/catal...ult#ps-sellers


Have you considered the cost of building your own?
What are you going to do about audio?

[olyteddy]

Sure, why not? $80 -vs- about $5, plus the fun of building it yourself...And per the OP a simple 'Y' for the audio will suffice...Or add another couple of bucks in Op-Amps and build an audio distribution amp too. (not needed with 'RCA' audio)...Anyway, the OP was about building one.

[SingSing]

I have not buy op-amp for quite a while, because they are free. National semi, Analog Device, TI, Maxim will send them to you free, just sign up an account with them.

[olyteddy]

Amen that. I got a lot of Maxim stuff that got built into the local public access station before we could afford 'real' distribution amps and swicthers...

[sanlyn]

Sure, why not? $80 -vs- about $5, plus the fun of building it yourself...And per the OP a simple 'Y' for the audio will suffice...Or add another couple of bucks in Op-Amps and build an audio distribution amp too. (not needed with 'RCA' audio)...Anyway, the OP was about building one.

Hooray on that, olyteddy. I built a lot of Heathkits (even a color TV!) way back when, some Dynacos, etc., and even an old RCA mono amplifier with Radio Shack parts -- all with considerable satisfaction. But you might keep the CE Labs line suggested by EdDV in mind. It's mighty nice stuff.