In an electrical system, a ground loop or earth loop occurs when two points of a circuit are intended to have the same ground reference potential but instead have a different potential between them. ( July 2014) ( Learn how and when to remove this template message) Please help improve it to make it understandable to non-experts, without removing the technical details. Note that you cant use the VRD-1FF between a DSS dish and receiver, because the capacitors cant pass the DC power that the receiver supplies to the dish.This article may be too technical for most readers to understand. I recommend using the VRD-1FF along with one or more CI-2RR isolators to provide complete effective ground isolation between video and audio systems. The capacitive isolation approach is superior to the cheaper transformer alternative, and is well worth the extra expense. Subjectively, the VRD-1FF yields the clearest, sharpest picture of all of the isolation devices I have tried. These connectors incorporate a gold-plated, crimped center pin, rather than relying on the cables flimsy center conductor. The LV61S is a flexible, high-quality RG-59 replacement, and the Canare F-connectors are the finest made. No corners have been cut here either the jumper uses Canare LV61S cable and Canare FPC4 F-connectors. Because the VRD-1FF has female F-connectors on each end, Jensen also supplies the short jumper cable shown in Photo 3. Retailing at $69,99, the VRD-1FF is not cheap, but it boasts the high-quality construction and performance I have come to expect of Jensen products. If it exceeds 34V DC or peak AC, you have a grounding problem that must be corrected before using this or any other isolation device! Check the voltage potential between your CATV line and the RF input to your video system. However, Jensen notes that the VRD-1FF should not be used in situations where the DC or peak AC voltage between input and output exceeds 34V. According to the VRD-1FF datasheet, the capacitors in the VRD-1FF are rated at 200V DC. The device is compatible with analog, digital, and HD systems, as well as modems. Jensen specifies the 50MHz insertion loss at 0.01dB typical and 0.1dB maximum. One advantage of the capacitive isolator is extremely low insertion loss in the operating range. The VSWR (Voltage Standing Wave Ratio) is specified as 1.08:1 from 50MHz to 866MHz. Jensen claims a bandwidth of 1MHz to 1.3GHz ☓dB. At the power line frequency of 60Hz the device has extremely high isolation impedance, 1.3M?, but the impedance is very low in the RF region. According to my measurements, the device consists simply of two series capacitors, one in the signal path and one in the ground path. The Jensen VRD-1FF CATV isolator is unusual in that it is the only Jensen product that does not use a transformer (Photo 3). The supplied pigtail cable uses high-quality Canare F-connectors and Canare LV61S cable. Picture quality is visibly superior to transformer-coupled CATV isolators. This CATV isolator is capacitive, resulting in extremely low losses over a wide bandwidth. Photo 3: The Iso-Max VRD-1FF is the only product made by Jensen that doesnt use a transformer. Parts Express sells a similar device, the Dayton VIT-1, part no. This 75? to 75? isolation transformer costs less than $10. When in doubt, use an ohmmeter to check for continuity between the 300? and 75? sides, both signal and groundresistance should be infinite.Ī more elegant solution to CATV ground isolation is Xantechs model 63400 Ground Breaker. They are not baluns, and do not provide ground isolation. Some devices labeled matching transformers use an autotransformer. I have seen cheap ones that were actually nothing more than feed-through adapters no transformer, no impedance matching, and no ground isolation. But, it did cure the hum problem.Īnyone opting for this cob job approach should beware of certain devices being passed off as balun transformers. Garden-variety balun transformers typically have an insertion loss of around 3dB, so the total loss of this solution was around 6dB. My solution was to connect the 300? ends of a pair of 75? to 300? balun transformers back-to-back. I first ran into this problem around 20 years ago, before CATV isolators were readily available. A pair of Jensen CI-2RR stereo isolators are used in both the recording and playback signal path, providing ground isolation in both directions. Figure 6: A typical audio/video application for recording and playback.
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