Videolarm qfdpt3-50na 用户指南

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AC Voltmeter

Camera

Monitor

Bridge Tap

If you are experiencing problems, attempt to simplify your setup. Test 
each cable segment separately. For example, test the camera and 
monitor together without the other equipment. Then add in the NVT 
transceivers, back-to-back. Test each segment of a long cable-run 
independently. Attempt to isolate the problem.

Below are problems that may be encountered. If the suggestions below 
are not helpful, or the recommendations are not effective, please call 
NVT’s customer support. NVT customer support can be reached 8:00 
AM to 5:30 PM PST at (800) 959-9870 or at (+1) (650) 562-0600.

Possible causes include:

1. Shielded twisted-pair cable. Verify that the wire is unshielded 

twisted-pair cable. Multi-pair cable with an overall shield is OK.

2. Longer wire distance than expected. Be sure to include any coax 

cable that’s part of this distance. Verify end-to-end connectivity 
with an ohm meter. Measure the distance by disconnecting the 
transceivers, shorting the far end, reading the loop’s resistance 
at  the near end. See above for ohm vs. distance ratings. If 
necessary, replace transceivers with correct models specified for 
this distance.

3. Incorrect distance equalization setting. Adjust the equalization 

controls) with a mini screwdriver (NV-652R, NV-862R or the NV-
1662R). If the transmitter is an NV-653T, verify correct equalization 
switch setting.

4. Poor connection at a punch-block, splice, or coax cable. Re-check 

using the method described in #2 above, or use a wire test set.

5. Short between conductors of the twisted-pair. Use an ohm meter to 

locate the short.

6. Transient protection devices employing metal-oxide varistors. Use 

carbon blocks, gas-discharge tubes, or NVT transceivers w

i

th built-

in protection.

7. Check the camera. Are the focus and iris set correctly? Verify with 

portable monitor.

EXTREMELY FAINT PICTURE 

Only faint shadows of the original picture are visible. One of the 
twisted pair conductors is open or the wires are shorted together. 
Check with an ohm meter.

Adjust the distance equalization as necessary. Verify that the monitor 
has a 75 termination, not in “loop-through”.

Looks like a scrambled Cable TV signal. Check polarity.

1. Make sure that you are using unshielded twisted pair wire. 

2. Check distance equalization settings. 

3. For installations with passive (non-amplified) transceivers at both 

ends, check for ground loops. This may be done with an AC 
Voltmeter, as shown below:

  If the voltage is greater than 1/2 volt, use an amplified receiver, 

such as the NV-652R, NV-862R, or NV-1662R.

  Alternately, remove the ground at one end (usually at the camera 

end). Be sure that floating the camera conforms to local/regional 
and National Electrical Codes. 

4. Check for crosstalk from a second video path. Disconnect all other 

video sources. If the problem goes away, check for a split-pair or 
un-twisted wire.

These are caused by crosstalk from a second video path, or with 
ground-loops in installations employing passive models at both ends. 

1. To identify, disconnect all other video signals temporarily. If the 

interference goes away, check the wire to make sure the signal is 
traveling through a twisted pair. Is two-way video being sent more 
than 1,000 ft (300m) over Category 2 or 3 wire? If so, the send 
and receive signals may need to go in separate jacketed cables, or 
upgrade to Category 5 wire.

2. Next, check for ground loops. See #3 above.

Check the blue “power” LED on powered NVT units. If the light is not 
on, the receiver is not getting power. Re-check the power source and 
connections. 

If the green LED is on but the power LED is off, check that the power 
supply is floating. Grounding one side of the power input may cause 
this condition.

The NV-652R, NV-862R or NV-1662R series receiver/hub is not 
detecting a video signal. There is an open or shorted connection. 
Use a multimeter to locate the fault. 

Faint shadows of the original signal shifted to the right. This is 
caused by an impedance mismatch along the wire. Verify that the 
monitor is terminated with 75 (not in “loop-through”.) Check that all 
wire is unshielded twisted pair. The high-frequency wire impedance 
should be 100. Check for bridge-taps (see below) either by inspecting 
wiring closet connections, or, if available, using a “Time-Domain 
Reflectometer” (T.D.R.), sometimes called a “cable tester”.

If the faint shadows are not copies of the original picture, but from the 
picture of some other camera, check for crosstalk:

Is any portion of the wire un-twisted?

Are the signals from two cameras split between two pairs?

Is there a short between a conductor of one signal and a conductor 
of another?