|
…work best in
those circumstances where interference is caused by small differences
in ground potential (less than 20 volts) or by induced currents in
long cable runs. When there are multiple power panels in
a building, or even on a single floor, equipment and lighting loads
result in small differences in potential which induce ground loop
current flow and 60Hz. hum.
Electromagnetically-induced currents in long
cable runs also create hum. For 50Hz. and 60Hz. power systems, and
where induced currents are high, the HEC-2000 and HEC-2000H increase
the attenuation at the power frequency.
Should a small amount of hum remain after an HEC
has been added to the circuit, a second HEC can be added in series,
without significant degradation of the video signal. |
…are effective for
video signals up to 30MHz---encompassing HDTV frequencies--- with
little distortion. For signals below 20MHz, they are totally “transparent.”
Since hum reduction, using VNEs, is not as great as with HECs, their
use is recommended only where higher frequencies are involved. |
Breaking the ground connection in
video transmission lines will eliminate 60Hz. hum caused by ground
loops. When there are hum problems caused by large potential
differences (20 volts or more) the VIT is the product to use. The
dielectric withstanding voltage of the VIT os over 500 volts at
DC. VITs are true isolation transformers—there is no DC path
between the windings. Frequency response is flat over the range
20Hz. to 4.5 MHz. VITs also remove the hum created by
electromagnetically induced currents from power lines or distribution
systems.
IMPEDANCE IS BALANCED -
INPUT and OUTPUT
Note: Provision must be made for DC Control
signals - such as camera controls - which VITs will block.
|
