Keep in mind the video signal used in CCTV equipment is nominally a one (1) volt peak-to-peak signal and is impedance sensitive to 70 ohms for ideal video reproduction at the monitor. If these parameters are not kept, then the video will degrade.
If the installation of a system requires viewing the video at multiple locations from a single camera, there are a few different ways of accomplishing this. One way is through using a distribution amplifier. This device basically takes the single video signal and reproduces the exact signal into multiple outputs.
So if the input signal is a one (1) volt peak-to-peak signal you will get four (4) output signals of the same amplitude. Providing the run distance for the type of coax used is kept within the specified length, no other equipment will be needed to reproduce a nice clear video display on each monitor.
Due to the many factors that can effect the video signal (as in transmitting a nominal video signal level) directly out of the camera, through RG59 coax to a monitor, while still producing a clear video display across the entire length of the coax. In this case the coax should not exceed 750 feet.
However, let's say you need to use RG59 because it's more flexible and much easier to work with but the cable length must be 1,500 feet. The signal at this point is going to be weak and will display a very degraded picture on the monitor. As mentioned, there are many things that can effect signal strength before the signal reaches the monitor. If you find a weak signal, simply pass the weak signal through an equalizing amplifier, make the required adjustments, and once again there will be a good, strong signal that will produce a nice picture.
A post-equalizing amplifier means that the device will be located close to the monitor. There's an advantage to this design in that AC power is usually more readily available at the monitoring location than it is somewhere back up the coax line, and with this type of design it only requires one person to view the monitor display while at the same time making the required adjustments to obtain the nominal signal level.