I saw a couple robots online that used an rf modem to send and receive data and a video transmitter to transmit the picture from just one camera. i was just curious. plus with long range ethernet, the band rant is not the reliable for video transmittion, let alone three. and at $500 a pop for a video transmitter and reciever multiple just isnt cost effective.
Depends.... An rf modem is going to give you a bandwidth of something like 54kbps at best, which isn't fantastic. With wireless ethernet, you can get up to 300 feet of range in outdoor conditions, and ideally 54 mbps. If you use some good antennas, you can augment that range... And you can get even more by amplifying the signal, if you are willing to do that. Of course you won't get the full 54 mbps, but even if you only get an eight of that, it should be enough for compressed video streams.
Wireless video transmitters could possibly get you more range, but they are analog devices, and the more the distance, the more noise you will get at the receiving end, which isn't always practical with robotics applications.