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About Hum

Understanding & Eliminating 50 Hz & 60Hz Hum

pg Info_Srv/hum

RF transmission in cables is routinely plagued by 50Hz. or 60Hz. hum or other interference.  When a cable is used for video signals, small electrical currents caused by differences in ground potential (ground loops) or induced common-mode noise, can result  in considerable hum interference. Cameras, video recorders, monitors and video effects generators…even switches and computers downstream…are affected. 

Allen Avionics manufactures three types of products to eliminate hum caused by ground loops or induced currents. All are broadcast quality. Although they can be inserted any-where in the transmission system, they are most effective at or near the end of the cable run.

Hum Eliminaors
 Model HEC

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Video Noise Eliminators
 Model VNE

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Video Isolation Transformers
 Model VIT

…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.

Note: Provision must be made for DC Control signals - such as camera controls - which VITs will block.

Hum vs. Noise…
What’s the Difference?

Simply stated, for video application there is none. Hum eliminators and video noise eliminators only remove unwanted 50Hz. and 60Hz. signals from video cables.


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Allen Avionics, Inc.
2727 Clinton Street
River Grove, IL  60171
Phone: (708)-453-3238
Fax: (708)-453-0297
E-Mail: Sales@AllenAvionics.com

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