My suggestion is that you use an amplifier or converter.
Composite video is not specified to even work at 150 meters (That means 450 feet)at all due to the chroma and the luminance signals getting out of sync with one another.
The fact that you managed to get the pd170s to work that far was fortunate. I have had trouble getting my pd170s to work reliably past about 150 feet.
Since you are pushing the spec, you just happen to have some above average line drivers in the camera and cables. The nxcam line drivers are probably similar but not exactly the same.
Option 1. Buy a small composite amplifier/buffer. You can get cheap ones from radio shack or you can get ones for about $400 which allow you to actually add gain to compensate for the loss of signal. You can put this buffer right after the camera, or half way down the line.
Option 2. (better) use the sdi output through the bnc connector. It is specified to actually work the distance you are talking about. In this case you will need to buy an sdi to composite convertor and place it at the end of the cable run before the analog switcher. These convertors are about $1000.
John Lenihan
LeniCam Video Productions
972-378-0446
https://www.lenicam.com
John Lenihan
LeniCam Video Productions
https://www.lenicam.com