Can 2.4 ghz, 900 mhz serial and DC share the same line?
W9GFO
Posts: 4,010
Hi all,
I'm trying to figure out if I can build a remote pan/tilt camera head with other sensors that can be dropped a couple hundred feet (up to 500ft) down a well with materials I already posses.
I already have a couple of 2.4 ghz wireless cameras, one camera with standard NTSC OUT, loads of RC stuff, hundreds of feet of coax and hundreds of feet of CAT 6. Ideally the camera head would have the camera, a couple servos, some sensors (pressure and temperature for example) and an array of leds for lighting. The sensor data would be overlayed onto the video picture at the surface.
Is it possible for a single coaxial cable to carry DC, Video and telemetry? I'm thinking of using 12 VDC for power, 2.4 ghz for the video and 900 mhz for the control of the servos and receiving sensor data. Alternately, I could use the CAT 6 if not practical to use coax, though I would prefer to make the coax work.
Since there would be huge losses of the 2.4 ghz signal along the coax, would it be better to just connect it directly to the receiving antenna jack or should there be an antenna on the top end of the coax? Hmm, it just occurred to me that there would be 12 VDC on that line so I guess there would have to be an antenna.
Thanks,
Rich H
I'm trying to figure out if I can build a remote pan/tilt camera head with other sensors that can be dropped a couple hundred feet (up to 500ft) down a well with materials I already posses.
I already have a couple of 2.4 ghz wireless cameras, one camera with standard NTSC OUT, loads of RC stuff, hundreds of feet of coax and hundreds of feet of CAT 6. Ideally the camera head would have the camera, a couple servos, some sensors (pressure and temperature for example) and an array of leds for lighting. The sensor data would be overlayed onto the video picture at the surface.
Is it possible for a single coaxial cable to carry DC, Video and telemetry? I'm thinking of using 12 VDC for power, 2.4 ghz for the video and 900 mhz for the control of the servos and receiving sensor data. Alternately, I could use the CAT 6 if not practical to use coax, though I would prefer to make the coax work.
Since there would be huge losses of the 2.4 ghz signal along the coax, would it be better to just connect it directly to the receiving antenna jack or should there be an antenna on the top end of the coax? Hmm, it just occurred to me that there would be 12 VDC on that line so I guess there would have to be an antenna.
Thanks,
Rich H
Comments
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
Post Edited (Leon) : 1/11/2009 10:12:52 PM GMT
I think the simplest thing, from an operational standpoint, would be to encode your telemetry data in the NTSC's vertical blanking interval* and just use 75-ohm baseband video over your cable. (It's RG59U, right?) That way, with the batteries down the hole, you've only got one cable to contend with.
-Phil
* 60 fields/second * 8 blank lines/field * 2 chars/line * 10 bits/char = 9600 baud throughput.
Post Edited (Phil Pilgrim (PhiPi)) : 1/11/2009 10:37:17 PM GMT
Rich, if you're that desperate to get rid of them, I'd gladly take them off your hands.
-Phil
-Phil
Using ethernet for this would be a completely new thing for me. It seems like I would need special hardware to convert the NTSC into whatever travels over ethernet. I also don't want to have to use a laptop on the surface. I'm not against it, I just don't know anything about it.
Batteries down the hole are ok, just trying to keep the size down. I need at least three hundred feet, the cable is CAT 6 if that makes a difference. The coax is quad shield RG6.
I forgot to mention that I'll be pulling them back up out of the hole when I'm done. [noparse];)[/noparse]
Yes it has a steel liner, but the bottom will be under 100 ft of water.
That looks interesting (and cheap), still need a way to get the pan/tilt signals down though.
As I understand it the DirecTV sends DC voltage along one of the coaxes to switch the LNBs. That's what led me to believe that a coax could share dc and RF.
It would work out pretty well if I could use the 500ft of coax as a feed line for the 2.4 ghz and 900 mhz. The camera (and battery) would be three hundred ft down the well, the rest of the coax would be in a spool up top with a dual band antenna mounted to the spool. The receiving station would then have the normal 2.4 GZ receiver and 900mhz modem. The signal losses going up the coax would be tremendous but the needed range is only a couple feet. If the coax could also carry DC, then the battery could be in the spool.
-Phil
Rich H
-Phil
You can get Ethernet cameras, of course. Some have POE. An Ethernet repeater would get over the cable length problem. Compared with the cost of making the hole in the first place an Ethernet system will be good value, and very simple to implement.
How are you going to use the system if you don't want to have a laptop on the surface?
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
Post Edited (Leon) : 1/12/2009 4:10:47 AM GMT
A video monitor with an overlay for the data.
I've read that RG6 can handle CCTV signals in excess of 1,200 ft. Perhaps I will have to abandon the pan/tilt feature or, put an accelerometer in the camera head and use a series of tugs to tell the camera which way to point.
Rich H
I did an underwater camera once, like what Leon is talking about. It used 10base2 over coax with 10baseT converters at each end and an Axis Ethernet camera. The camera had an RS232 port and TELNET capabilities, so I was able to focus it remotely using a PIC with an RC servo. (This was before I got into Parallax stuff. A BASIC Stamp would've been easier to implement.) But here's the rub with such a setup: If your customer just wants a video recording with a data overlay, you've got to integrate all this stuff digitally. It's much easier just to overlay characters on NTSC video and record it. The other advantage to NTSC cameras is size. A simple CCTV board camera is much more compact and easier to house and manipulate (P/T) than any ethernet camera would be. I ended up enclosing my system in an underwater housing with a domed window, 19"L x 6"D. It was big and heavy, and I wouldn't do it that way again.
One thing you haven't mentioned (or I missed it) is what the telemetry data consists of and where it originates. Is it something like water temp from a sensor at the camera end, or well depth from an encoder on the cable reel? Or?
-Phil
All telemetry originates at the camera end. Temp, pressure and direction are the main things. They should all be on an overlay.
If need be, the video signal could be interrupted in order to send commands downward. .Hmmm, I am not sure how to tell the camera to stop its' signal though....
Rich H
That wouldn't be much different than the currently available cameras that just have a fisheye lens and a light that you drop down the hole. Needs to be able to stop and look at every welded seam both above and below the water. If it only needed to go to the bottom and look around I think autonomous would be very reasonable.
Rich H
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Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
I've got a couple boards I could try it with, but I've got to stay focussed on a current project for a few more days yet.
-Phil