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Troubleshooting UTP CCTV Systems
T
he use of Unshielded Twisted Pair (UTP) in CCTV systems
is increasing, as is an interest in identifying common pit-
falls or causes of poor video quality after installation. An
ideal UTP CCTV system consists of several simple com-
ponents, each deserving careful consideration in order to have a
hassle-free installation. The key to troubleshooting is recognizing
those ingredients. Compare the details of a problem installation
to an ideal one and observe the video to identify possible culprits.
Use these logical steps to reduce the time spent on the trouble-
shooting process.
When It is Not About The UTP
Camera is Adequately Powered: Veri-
fy the cameras input voltage is within man-
ufacturers tolerances under load conditions
(including heaters, blowers, etc.) With the
camera connected and operating, measure
the input voltage at the cameras power
input terminals. Typically, it should be
higher than 21 Volts AC for a 24VAC cam-
era, and 11.5 VDC for a 12VDC camera.
Camera is Properly Adjusted: Set focus, iris and shutter
speed using a portable monitor. It is worth noting that many LCD
monitors have internal Automatic Gain Control (AGC), making
brightness adjustments difficult. The use of a Video Level Meter
will result in more accurate levels, as demanded by todays sensi-
tive DVRs. Alternately, use an oscilloscope or an older glass jug
monitor to verify the signal.
Avoid Ground Loops and Transient Damage: A ground loop
Video
Surveillance
Troubleshooting
UTP CCTV Systems
Each system component deserves careful consideration
By Christine Baeta is a system-grounding problem that occurs when one device in
a system is connected to an electrical ground different from the
ground of the other devices. At low voltage, the ground difference
is detectable at voltages as low as 200mV, and can be identified as
a Hum Bar. At high voltage, it is identified as a lightning hit or
other transient. Large currents can travel through the wire to the
other ground, damaging equipment along the way.
Leaving the camera floating is a far superior approach
than local grounding. This may require rubber pads or plastic
screws, but it is well worth the time in lightning-prone areas.
Parking lot cameras or those mounted on metal-skinned
buildings are particularly vulnerable.
If a transient protection device is used, place it right at the cam-
era. Connect the protectors ground wire to the cameras chassis
(or shield of the BNC connector), rather than the local ground, to
prevent transients back-flushing into the system. This single-point
grounding practice is highly effective for both high-voltage tran-
sients and low-voltage ground loops. These practices should always
be subject to regulatory safety requirements such as Electrical Code.
Ground loops can also occur between cameras connected
to a multi-output power supply if one or more of the cameras
has an additional path to ground. Most multi-output power
supplies do not isolate outputs from one another. Instead, con-
sider powering cameras and peripheral equipment using sup-
plies with isolated outputs.
Getting Ready For Twisted Pair Video
Use Correct UTP Transmitter and Receiver: Confirm dis-
tance by taking a resistance measurement of the wire, and use
the transmitter and receiver specified for that distance. If power is
required for the UTP device, ensure that the power supply in use
conforms to the UTP transceiver manufacturers specifications.
Wire and Connections: Use unshielded twisted pair Cat-
egory cable. Use conductors that are twisted as pairs. Do not
double up pairs for video or use any untwisted wire. Do not
use shielded wire. An exception is multi-pair wire (6+ pairs)
with an overall shield, or wire that is specifically rated Cat5 or
better. Test wire pair using a Wire Map Tester, and verify RJ45
connections. If wire is likely to come in contact with water
(buried or in underground conduit), ensure that moisture-
resistant cable is used. Water will damage unprotected cable.
Head-end Considerations: Correctly adjust the UTP
CCTV receiver as needed, per manufacturers instructions.
Verify the control room receiving equipment has one (and only
one) 75-ohm termination, and that it is at the end of the trans-
mission path. For best receive-end level adjustments, tempo-
rarily connect the video signal from your UTP receiver directly
to a video level meter, oscilloscope or monitor that does not
have AGC, bypassing the DVR or other receiving equipment.
If plagued by poor or no video when installing or servicing a
UTP CCTV system, use observations to identify possible causes. It
may be necessary to test each cable segment separately. For exam-
ple, test the camera and the monitor together without the other
equipment. Add in the UTP transmitter and receiver back-to-back.
Test each segment of a long cable run to isolate the problem.
Video Symptoms and Solutions
Faint or blurry picture with little or no color: This symptom
most often indicates loss of signal strength. Check for excessive
wire distance, incorrect equalization of adjustable UTP transmit-
ter or receiver, improper camera adjustment or output level, the
use of shielded wire or water damage to wire. Testing for possible
water in the line involves measuring the capacitance between the
conductors that have been disconnected from other equipment.
Cat2 or 3 wires should read 19pf per foot or wire; Cat5 is 16pf per
foot. (Example: 1000ft of Cat5 should read 16nf or .016µf).
Extremely faint picture with only shadows of an image:
There is likely a wiring problem such as an open conductor or
short between conductors. Verify using an ohmmeter.
Over-saturated colors, high-contrast, grainy, bright, wavy or torn
image: This could indicate incorrect equalization of the transmitter
or receiver, improper termination or a ground loop problem. To mea-
sure for a ground loop using an AC voltmeter, test between each UTP
conductor and earth ground. The reading should be less than 200mV.
Image out of sync: This could indicate incorrect equalization
or a ground loop. But it is also indicative of reversed polarity if the
image appears scrambled or as a negative image.
Faint stripes or bars gliding up or down in the image:
This usually indicates crosstalk, which occurs when nearby
signals are induced as noise onto the transmission path.
It most frequently occurs when
untwisted wire, mis-wiring or infe-
rior baluns are in use. Not all UTP
devices are created equal. Noise
can also easily be induced onto
coax in the path. Horizontal, roll-
ing bars indicate ground loops.
Random lines, noisy image or faint
shadows from the image of another
camera: Crosstalk is the most likely
culprit.
Ghosting faint shadows of
original image shifted to the right:
This is an indication of an imped-
ance mismatch, most often the
result of a bridge tap an extra-
neous length of dangling, un-ter-
minated cable connected to the
transmission line. Locate and
remove bridge taps, and check for
extra conductors at punch-down
connections. Ghosting can also indicate improper termination.
No video, flickering image or signal LED: This could
indicate a poor UTP or BNC connection. It could also be the
result of an intermittent signal originating from the camera.
Verify the camera is not experiencing a brownout condition
due to insufficient power.
While wiring problems, signal level issues, ground loops and
improper termination are the most commonly identified culprits
when troubleshooting UTP CCTV Transmission Systems, product
failure periodically occurs. If you suspect a transmitter or receiver
has failed, replace the device with a known good device or con-
tact the manufacturer for support and any recommended testing
procedures. Armed with the correct test equipment and the facts
about common UTP transmission issues, dont be surprised if
your troubleshooting hours are significantly reduced, leaving you
more time to design and install new systems.
Christine Baeta is technical services manager for
Network Video Technologies Inc.
This image is the result of a
ground loop issue.
This image is the result of an
interference issue.
Network Video Technologies
800.959.9870 +1 650.462.8100
www.nvt.com info@nvt.com
Reprinted with permission from Security Technology & Design magazine September 2007