Re: Video and power
IanP said:
First of all, measure the resistance of the core and the shield to estimate dc-loses in the cable ..
Next, connect video from any source (video generator, camera, vcr ..) to this cable and observe (connect the other end to video-in of any TV, monitor ..) what is the quality of signal that passes through ..
Is the coax electrically isolated from the steel?
Regards,
IanP
Power feed capability is important, but check video signal capability on this long distance first!!
1000 meter is long distance for video in base band and you can possible see unwanted effects as bluring or tex. 'H' -> '|+' depend of low resp high frequences have different loss and traveling speed in cable, also after using amplifier to composate loss in cable.
frequency range from 50 Hz to 1 MHz in coax is very vary depend of frequency both in loss and group delay and can give affect on video quality. This effect can only see on very long cable test and not see in testing short cable length in lab.
This effect is near impossible to fixing up afterward with filters or equlizer ie. part of distorsion is depend of group delay distorsion [1].
And take care of loss (attenuate) in cable, most case video input have not som much dynamic lower than video:s 1 Volt p-p
Test if you can make acceptable video quality on _whole_ cable length (without DC-feed in first try) connected to selected cable drum before costly cable installations job - is more or less catastrophic for you or companys economy if you find out cable is unusable for you application and need installation new other type of cable and/or equipment again....
Is not guarantee of enough video quality on 1000 meters also if looks nice testing on 500 meters cable drum - test whole length!! my experience with radio and leaky/radiating cable say me always latest few hundred meter from end have very big influences if projekt going succefully or not...
Remember: most thing in transmissions line world have ' y^x' in rules depend of distance. Nothing happend in first short distance (x) even if 'distorsion of any kind'
is quite high per meters, but in long distance is closest possibly value to '1' on 'y' importent to make project succefully or not, and very much happens in latest few hundred meter from end side...
ex.
(ref 1 Volt p-p input on cable)
99.9 % power left per meter cable (att. 0.1 % power or -0.0043 dB/m)
0.999^10 = 0.99 power left or 0.995 volt p-p after 10 meter
0.999^100 = 0.948 or 0.9512 volt p-p after 100 meter
0.999^500 = 0.6064 or 0.7787 Volt p-p after 500 meter
0.999^1000 = 0.3677 or 0.6064 volt p-p after 1000 meter ( att. 4.3 dB )
99.7 % power left per meter cable (att. 0.3% power or -0.0132 dB/m)
0.997^10 = 0.9704 or 0.9851 volt p-p after 10 meter
0.997^100 = 0.705 or 0.8605 volt p-p after 100 meter
0.997^500 = 0.2226 or 0. 4718 volt p-p after 500 meter
0.997^1000 = 0.0496 or 0.2226 volt p-p after 1000 meter (att. 13.2 dB )
even small change of cable parameter can give costly result, i first case with 99.9% power left per meter possibly not need video amplifier before equipment after 1000 meter
but using cable at 99.7% power left per meter you need using extra videoamplifier depend of 0.2 Volt p-p video signal is not good for videomonitor after 1000 meter.
etc.
Very small change on 'y' parameter from estimated calculated value in real world, in wrong direction can increase cost very much or ruin whole installations/functions on very long cable distance project. Right cable select is very importent here...
[1] is possible with allpass-filters , but > 90 percent of filter books skip this chapter to how calculate and build analog all pass-filters with wanted parameters and mostly decribe only digital FIR-filters for equalzing already sampled digital modulated signals...
/Xxargs