RS-170 Video Amplifier Suggestions Needed

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NV185864
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RS-170 Video Amplifier Suggestions Needed

Post by NV185864 » Mon Mar 13, 2006 8:26 pm

I am using a small marshall electronics black and white video camera to transmit video via a coax cable. I want to extend the range of my system but better coax is very expensive and or much larger in diameter. I know this is a problem that has been tackled before. I can tolerate losing half of my voltage before my VCE card refuses to show anything.
Can anyone help me with the math on this. I think 1/2 voltage is equivalent to 6dB's or 1/4 power. I am using an RG ? cable with .78 dB loss per 100 feet. (Sorry I cannot recall the RG number off hand. I'll post it as soon as I look at the cable again.) I'd like to at least use a smaller coax for the current 1000' foot system. (Smaller but not more expensive)
Searching video amplifier on Digikey and google give overwhelming number of results. Does anyone have any suggestions or direction?
Oh and I think I want to amplify at the camera end of the cable. Is this correct? I'd go wireless if the camera was above water.

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Robert Reed
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Re: RS-170 Video Amplifier Suggestions Needed

Post by Robert Reed » Mon Mar 13, 2006 9:33 pm

Your math is correct, but theres still a few missing peices.At what frequency(s) are you operating on? A rating of 0.78 db loss per 100 ft. is quite lo. Also have you thoght of using cheap boosters along the way or at the head end ? a 20 db amp would not be that expensive and would certainly offset cheap cable losses. I am not sure if any of this is feasable since you end your post with "under water" ???? please clarify.

NV185864
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Re: RS-170 Video Amplifier Suggestions Needed

Post by NV185864 » Tue Mar 14, 2006 6:37 am

Bigger picture: Nothing can be larger than 1.75" in diameter. This is an underwater camera for a water well or pipe line. I've looked into off the shelf boosters and none are small enought to fit in my housing. Putting them inline poses leakage problems. Yes .78 dB is lo but the cable is almost .35" in diameter.

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Re: RS-170 Video Amplifier Suggestions Needed

Post by jimandy » Tue Mar 14, 2006 8:44 am

I don't know if this is an option or not, but what if you sent a modulated RF signal back up the line? Would there be any distance advantage?
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Re: RS-170 Video Amplifier Suggestions Needed

Post by rshayes » Tue Mar 14, 2006 9:25 am

Another possibility is to use FM modulation on a moderate frequency carrier, possibly in the 10 to 20 MHz range. This should be able to operate even with 20 or 30 db of attenuation. The MC4024 VCO might still be available or there may be newer chips for this purpose.

A second alternative would be to use fiber optics. The cable is smaller than coax and may be cheaper. Connectors and terminal equipment are more expensive, but at the 1000 foot range the overall cost might be comparable.

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Re: RS-170 Video Amplifier Suggestions Needed

Post by Robert Reed » Tue Mar 14, 2006 11:52 am

There are small VHF thru UHF amplifiers available that would fit your size restriction requirements. Most of these would offer 20 db gain and are available with remote power options. That is to say it would be powered by a supply at the tail end. these are inserted in series at the head end with suitable DC blocking and power fed thru the coax. They are usually set up for 50 ohm in/out impedances. I have seen these from a lot of manufacturers over the years, but you could start with Ramsey Electronics or do some googling. Maybe you already have a DC source running along side your coax for camera that you could use. It sounds like everything is running in some sort of conduit. Again I dont know what mechanical difficultys you would encounter for installing one of these.

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Re: RS-170 Video Amplifier Suggestions Needed

Post by Ron H » Tue Mar 14, 2006 12:35 pm

If you decide to stay in baseband, a video equalizer is useful(necessary?), because loss is frequency dependent. I don't know if this particular design has enough adjustment range for your application.

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Bob Scott
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Re: RS-170 Video Amplifier Suggestions Needed

Post by Bob Scott » Tue Mar 14, 2006 4:06 pm

A long time ago I repaired a similar industrial "Sewer Camera" for hunting down broken pipes and tree roots in municipal sewer trunk lines. They modulated (FM) the video before running it down the cable using the recording modulator/head driver circuits copied from a VCR. Um, they actually ripped the video recording circuitry out of a new Sony Betamax VCR, and ripped out the playback circuitry for use at the other end of the cable.

Surely you should be able to find a TV Ch3 or 4 modulator suitably small enough and do the job just as well?

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Chris Smith
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Re: RS-170 Video Amplifier Suggestions Needed

Post by Chris Smith » Tue Mar 14, 2006 4:52 pm

Most amps trade off current for signal voltage so any amp up strem will cover your loss.

When adding in multiple thousands of feet of line, small amps can be placed along the line to make up for almost any signal loss.

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Re: RS-170 Video Amplifier Suggestions Needed

Post by NV185864 » Wed Mar 15, 2006 7:12 am

Fiber optics would be sweet. But I would need a removable connector. I think linear technologies has the best solution for me. I'm going to get some LT1256's and some other amplifier chips from LT and play around until I get it. RonH I believe the application note design does have enough range for me. I think I will still need an amp at the camera end of the cable. Any suggestions on which amplifier chip to use? There are many options from LT.

Thanks for all of the great suggestions everyone! I will look into the VCR demolition, the RF modulation schemes and the small inline amps too. But these options don't appeal since I wouldn't need to do a board layout and lots of circuit prototyping.

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