Electronic – Coaxial/UTP Equalization Circuit

operational-amplifiertransmission linevideo

I have a problem with a circuit that transmitts a video signal(PAL 1.0 Vp-p) through a coaxial cable of around 200m.My problem is that the high frequency content is really attenuated by the cable.I need to build an equalization circuit but I don't understand how I will do it because the attenuation doesn't appear only at a certain frequency,so i will need to correct every "frequency".Could somebody give me some advice about this,where do I need to put the equalization circuit(transmitter/receiver) and how do I suppose to do this ?I thought at an active high-pass filter but this will work only for a certain frequency.

Best Answer

I think you'll do just fine with equalization. RG59 (Belden 8212) is pretty good coax and you can find the attenuation figures HERE for virtually any commonly available coax - it's a calculator so just plug the numbers in i.e. frequency, cable length etc. and bingo out pops the attenuation: -

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It's really not a hard cable to equalize up to 10MHz (attenuation about 6.5 dB at 10 MHz and I would suggest that pre-emphasis is the best way to go (then your receiver isn't going to be too upset).

So, plot out the counter-response you need and make a peaking filter that roughly matches the emphasis you need to apply. Use (free) LTSpice for this or any PSpise software to hand.

I've had to do this for 660 Mbps over 50m of very good coax but it still benefitted from a bit of emphasis. In the end we decided to use CAT7 but the idea was proven as far as I am concerned.

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