how can we test if video balun is good ?

As in if it works? Connect it to a camera and a monitor.

What are you asking here? Bandwith, clarity, what?

Erron S.

for testing passive balun using a multimeter.

Best way is to send a test signal and on the dvr end use an oscilliscope...or you can buy pretty straight forward testing equipment

ok. thanks

For RS-170A OR NTSC compatible video (analog CCTV) you should use a multiburst signal and waveform monitor. Most baluns are just autotransformers which match the 75 ohm impedance to 100 impedance of the UTP cable.

We tested a few different baluns last February, using a couple of cameras and an FM Systems CM-1 Camera Master tester. A links to the results is below:
http://www.cctvforum.com/viewtopic.php?t=11664

Using an NTSC waveform generator will represent the perfect camera. Specifically, the multiburst signal is ideal for testing frequency loss effects due to transmission media (UTP, coax, wireless etc). This is standard practice in broadcast TV for many decades.

Yes, but they can be somewhat expensive. Considering that many cameras put a reference signal in the blanking interval, you could use that as the test waveform with an oscilloscope monitoring it. The color burst signal is available on all color cameras and, at 3.58MHz, makes a reasonably good test signal, as long as you measure directly at the camera first for a reference level.

if you want to know if the balun can avoid inteference or not. just install it in elevator, if the enviroment not good, it will have wavelet on the screen.