I have a bit of a secret project on the backburner that is waiting on finding a suitable wireless solution for it. it requires a long range wireless Rs-232 serial connection and video transmission.
$479 for the module and modem for a 40 mile data link sounds pretty good. They have USB and Ethernet versions as well. But I’m not sure how I could incorporate these to transmit my Video feed. The Feed would likely be in NTFS_m format.
I guess it would depend on what your threshold is for the amount of video data you can send at max. 115KBaud is. It’s either going to be real small, a real slow frame rate, or a real lossy compression at 11.5Kbytes / second.
I seriously doubt that these will get anywhere close to 40 miles at 900 Mhz. 1W is a lot of power, but from my WiFi experiments and from what I know people did with FM transmitters and the like 1W (antenna included) should give you about 3-5 miles, not 40. Also, check on the datasheet. They only claim 3000 ft in an urban environment. This makes me really question the 40 miles as being essentially the ultra best case line-of-site in the middle of the desert and not anything close to real world use. Also who knows what antenna they were using for that. Household WiFi gear can get 7 miles with a directional antenna, easily. Uidirectional WiFi links at that range can also be had with a little work.
Anyway…that said, depending upon the range you need for the project, this could work. However, if you really need > 5 miles, you probably should look elsewhere.
As far as your video, ideally you could put some kind of miniPC in this project. A Bt848 video capture card (others would work too, but Bt848 is cheap and well supported) would allow you to take in an NTSC (I’m assuming you mean this, as NTFS is the Windows file format) and encode it to whatever digital form you want. It could then be streamed over any type of wireless networking link. The specifics here really depend on your range needs, bandwidth capacity, and processor. A 5-10Mbit link with a fast processor (Xvid, RealMedia, Mpeg4s, etc. codec), could give almost 640x480 30fps.
For around $450 I would make or buy a slotted waveguide antenna or cheaper directional (< $200) and buy a good bidirectional WiFi amplifier for my base station ($100), then use a high wattage card on my device ($100) seattlewireless.net/HardwareComparison. The slotted waveguide would be easy for you to make, it is essentially an aluminum stud with slots cut in it, they need to be a specific length and in a specific pattern, but a router would do it just fine. If all else fails you can buy them premade for around $150.
Do note that the “up to 40mile range” is line of sight, and in urbane settings (aka.trees and such) it is “up to 3000’”. You can do some video at the rs232 baud rates, as back in the mid 90’s I used to run cuseeme over a 14.4 modem. What is the data transfer format you plan to use on this serial connection?
I agree, the “40 mile” thing is extremely optimistic.
Signals at VHF/UHF frequencies propagate rather poorly through any sort of obstacles, including trees and buildings.
If you really need that kind of range, you need one or more of the following:
Operate at a MUCH lower frequency (not really an option).
Operate at a MUCH higher power (not really an option).
Operate through an existing repeater. This is what HAMs do to achieve muli-mile comms at the higher frequencies.
Thanks guys. I figured the range was a bit exagerated. Power and size is not an issue with the “thing” itself. It will be running a laptop onboard, and 6 ATV batteries with a current weight of 95 pounds so far.
So really, I can mount just about anything that can run off a 36V or less power supply. After getting some advice on this, I’m looking into radio licences and 400mHz transmission over 1 Watt. I’m going to find out what I’m allowed to broadcast and what I’m not. The video feed and RS-232 transmission can be by seperate means if necessary. But I must have a wireless serial connection.
I was goin to suggest looking at these aerocomm.com/rf_data_modems/connexlink_radio_modem.htm they only claim 20mls but the band width is sort of puny but at $200 a pair or for a experiment kit they seamed the best bang for the buck.
i think i,m gonna go usb and use this parallax.com/detail.asp?product_id=604-00051
to run a web cam to my comp thru blue tooth or wifi dongle and hopefully
be able to "cut the cord " so i can make better progress with my prog
With a proper antenna and/or amp, WiFi gear (including the WiPort) is able to get great ranges. It really is a great protocol. Considering there will be a laptop in this project, I highly suggest using WiFi as it will solve your control and video problems.
Thats what I was expecting to hear. I think a WIFI module or Wiport module would work great with evolution’s project. I dont understand why people are always “bad mouthing” the wiport becuase of its limitations, but the main reason why people use it is to wireless control an object from a computer, and thats what it does best! I know there is someone on the forum selling wiport boards )v1 v2 and v3 and Im sure you can get a great deal off of him. You can buy the module and board for 90$$ from here: rcgroups.com/forums/showthread.php?t=637872 there only selling about 15, so if anyone wants them you’d better hurry.
If the rov is going to have a computer on board, then I would go with wifi to start with. You could probably use a wifi adapter on each computer in the ad hoc mode, or use an adapter on the rov computer and have a cheap wireless router up on a pole, to do the communication cheaply (geek link below). I made a directional antenna (below) and it actually works. Live video would be very easy with this setup using web cam applications.
thats actually really neat and looks simple to do. An idea for the recieving end, if you put the module on a modified rotational servo, you could have a micro figure out whcih direction the signal is coming from and have that rotate to where the signal is highest, that way you always get the best signal from wherever you are. Course, idk how good your programming skills are, but its something Ive been thinking of doing.
Im not entirely sure if this is possible with our hobby componenents but Ive researched on the Mars Rovers Spirit and Opportunity for two years about 2 years back, and they use this technology to have their antenna’s pointing wherever the signal is comming from when Mars is rotating.
Yup. I’ve never done that, but it is very possible to use servos to direct a highly directional antenna on the bot end. This project does something very similar to look for WiFi networks: smithstuff.net/steercan/Steercan.htm.
Also, thanks for the WiPort link (highly debating getting another one). I don’t know who is bashing the WiPort, but the only bad thing about it I can see is the price.
Thats similar to what i had in mind, im sure this could be done with an electronic compass and a micro. Im not sure if this does what I said but it is some sort of compass module: Link
Hmmm… you know, this would probably be absolutely dirt simple if he has a GPS unit at each end in addition to the compass module (and even that would be redundant if things were kept moving). Feed the position data back and forth in real time and two directional antennas should be able to track each other without problem.
GPS could work great for this (depending on terrain, believe it or not if an obstacle is in the way, the best position might not be a straight line which would put you back to scanning anyway) and considering the base station probably isn’t moving. Personally I’d use a slotted waveguide on the basestation and only a directional on the bot. This would let you have multiple long range WiFi bots.
If 100% signal wasn’t needed 100% of the time, the steerable antenna could simply move around until it found a good position (i.e. just how the project I linked to works), then use a simple algorithm (possibly with a compass) to adjust for movement, and if things get too out of wack find another good position via scanning. Assuming the bot isn’t moving large distances at once this would probably work well and avoid costly GPS modules (they’re like $75-150 each, right?)
Just google that and you will probably find some designs.
