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oxxyfx

Video Buffer Question

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Hello,

I read enough on this forum already to know - if I want to make 2 video outputs from one Airwave receiver - one for goggles and another vor recording - then I need a video buffer.

I ordered a few samples from Maxim - Max4205 or Max4217 seem to fit the requirements.

My question about this is as follows:

I have one video out from the receiver. I want to connect this to the input of both video buffers from the Max4205. I have a capacitor on the Video Out (470uF), do I need anything else - like a 75Ohm resistor to the ground? Maybe 2. one for each buffer?

Also on the tipical application scheme they show the buffer's output connected to a coax cable, then after the coax a 75Ohm resistor to the ground. Since all this is PCB mounted, and no coax on it anywhere, do I just simply put that resistor on the output of the buffer close to the RCA video connector?

Further more, the 2 outcoming Audios need to be splitted as well. Do I have to use the same technic as with the video - that means 2 more max chips, or that can be simply split?

Thanks, Ox.

Edited by oxxyfx

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Hi oxxyfx,

a couple of weeks ago I posted a schematic in the following thread:

http://www.rc-cam.com/forum/index.php?show...wtopic=1977&hl=

You can use it for your application exactly the way it is shown there, and use MAX4217 as the OpAmp. The schematic is similar to the circuit shown in the 4217's datasheet on page12, only that you don't need symetric power supply.

You can forget about the coax cable and the 75ohm resistor on the very right hand side. They are there just to show the entire function. Actually the represent the goggles video cable and it's input cable impedance. So it's not a part of your video buffer circuit.

Just connect the Airwaves video out pin to the left port of this buffer, where it's labeled "IN", and connect your goggles to the right side of "Rout".

Use exactly the same circuit for the second buffer, connect it's "IN" to the same node as the first buffer (to the Airwaves video out pin), and just leave "Rin" of the second buffer. The reason is that this is the termination for the Airwaves video output stage which must be terminated with 75ohms, and so it's needed just once.

Cheers,

Hartwig

Edited by Hartwig

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Thank you, this is clear enough. How about the question of splitting the audio?

Edited by oxxyfx

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the audio splitting : just join the wires !

the audio output have normally 100 times lower output impedance

than the input impedance of your TV and googles so no problems

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