Ninety

Try one of these ... I bet it fixes it.. there are much better solutions but as pointed out above.. it is a ground loop issue. Ground loop isolator

Is replacing both of the recording devices to one of the same company out of the question?

I think you are right on the money as far as trouble shooting goes.. What do the coax connectors look like? How are the conductors? How does the dielectric look? Do you know what they should look like? Do you know what a sucked out connector looks like? Are they compression? If they are crimp they should be replaced.. as well as the barrel.. I would suspect the underground is your culprit.. are all of the bad cameras fed underground? you take any pictures of the connectors?

Is there no where or no one within 5-10 miles that has internet you can use? maybe pay a monthly to help them with their bill? You could install a system.. but without any access to remotely it won't do you much good.. b/c if someone does break in they will just steal that along with whatever else of value there is... maybe signage and dummy cameras will serve as a deterrent from any further mischief

What I meant by hardline, was a good internet service location.. like the house on the property.. those ubiquiti's can travel pretty far with line of sight.. We just did a remote installation where there was really no other choice except satellite .. we used a company called via sat or Excede internet.. the cost is $60 a month for 5down 2 up with a cap of 10 GB a month.. supposedly they don't reduce your upload speeds once your limit is met. So you have a couple of options.. get your internet access from a home near by that is paying for service or get internet service there at the location. you can create a solar setup with batteries for power out at the unit itself.. I would find a dvr that has alarm inputs and relay outputs and set you security up that way... sensor the doors, maybe some motion detection alerts from the cameras or a PIR that is attacehd to the alarm inputs on the DVR/nvr itself. I've never used a 3g hotspot type of device personally .. but I would suppose it is possible to acheive what you want.. but I would make sure whatever device you choose, you have the option of hard wiring some sort of alarm system in with it.. keep us informed on what you decide.

What about this? Claims hdsdi up to 600' CCS RG6 http://www.unixcctv.com/_e/Paige_Brand_Cables/product/CB-X06-7X6AFQ2B1/Paige_cable_1000ft_RG6_Quad_shield_Coax_Cable_White.htm

What kind of system do you have? Are the IP settings correct such as the gateway? Do you have a router or is your system tied directly into the modem? maybe try a ddns setup? have you reset your dvr device or your Cameras?

300m to wifi? Or to a nice hardline connection? What about satellite internet?

There is a Tribrid CVI system that will do IP,CVI, Analog.. but it's a little pricy..around about 900 for an 8 ch. Why can't you do aerial? Is it out of the question? All utilities are underground?

I agree with the above.. HDSDI is your BEST solution but the hD cvi products are pretty nice looking..It's relatively new but all the hardware is warrantied just the same. Where are you located? An all in one out of the box system is hard to beat price wise but you will most likely not be happy with what comes in the kit and end up spending the extra money anyhow.. CVI is cheap and 720. The new building should be wired in both siamese Coax and cat5. I am willing to bet you will be happy with the cvi.. how high are you planning on mounting these cameras?

Interesting product..

What kind of system ? Can you give details on it?

Interesting.. I'm about to do something similar to this.. I'm not sure how the Spectra mounts as I've never seen one before. But I am planning on using 1 1/2" Rigid bent on a triple nickle bender into a large J hook.. strap it to the pole and mount the camera to the end of it.. now the spectra might mount a little differently then mine but you could always get a flat 4 hole flange that threads onto the rigid and you should be able to mount your camera or fab something up from there..

This is what I'm thinking.. have you tested your cat5 runs ? Are you certain that your connecters are properly seated? ie no suck out.. the wire is all the way to the end and is making good contact on each end? What wiring scheme did you use? I'm thinking it's a wire termination issue..