It is available from Cables & ConnectorsInc. Rich goes on to write: Unfortunately none of my local stores carry the CALRAD products, so Iwill have to mail-order it. Ground Blocker and Isolation Transformer. was kind enough to forward some information regarding one ready-made isolation device: Calrad 75-504 D.C. powerline path portion of the ground loop. In addition to being big, expensive, and sometimes noisy, these will NOT break the A.C. When seeking information on isolation transformers for CATV systems, be aware that there are several other devices used in electronics which are also called “isolation transformers” which are of no use on CATV systems. Ground loop problems and how to get rid of them (somewhere on this site is information on both building and buying isolators). Besides using the usual search engines, try ferreting around these sites: As i am presently both lazy and busy, you will need to refer to other websites for details on what is readily available in the way of CATV isolation devices. Fix the ProblemsĪn isolation transformer is a device which, in the case of cable signals, allows all the desired signals to pass freely, while interrupting ground continuity, hence breaking ground loops. So, if there were some way to isolate each of the A/V/computer systems in terms of ground continuity, yet still allow the full desired cable signals to pass, that should break all the ground loops and cure the problems. In fact, if my drawing had not been so sloppy, one could more easily see that each of these individual feeds supports 3 ground loops: two blue, one green. Looking again at the diagram, we see that most of the loop lines congregate along each of the individual cable feeds to each A/V/computer system. In this example, that means that our remedies will be confined to modifying the cable hookups. power cord/powerline side of the loops is both illegal and unsafe, consideration A above reminds us that we can forget about any changes here. Since we know that making any ground loop-breaking changes to the A.C. Which are the fewest changes with the maximum improvements?.The following considerations guide this process: Now it’s time to carefully scrutinize the situation, and start choosing changes to form an overall solution. The blue loops are attempting to show that, even if the cable line to the pole and the mandatory cable grounding block are disconnected, each pair of connected A/V systems still forms its own ground loop. This is thanks to the mandatory grounding of the CATV cable as it enters the house. Yes, it’s messy…ground loops usually are! The green loops are attempting to show that each system, all by itself, forms a loop between the powerline and the cable. Next, draw in the possible ground loops, in some easily visible manner (drawn in different colors here): Note that even though the actual TV-VCR hookup will have at least three of these cables (Left audio, Right audio, and Video) and possibly more, the tests showed that any one of these could form a ground loop, so only one need be drawn, for simplicity (and it does not really matter which one is represented in the drawing). In the drawing, the thicker lines represent the coaxial cable of the CATV system, and the thinner lines are either power cords or standard “RCA phono plug” shielded interconnect cables, for either audio or video. Only two of the video systems (one with a VCR, the other just a TV) and one of the computer systems were found to be able to contribute to ground loops, per the tests of the previous page, so only these systems were drawn, for clarity. In this hypothetical example, there were (an amazing) five televisions, two with VCRs, plus two computer systems with cable modems. Here is an example of several systems in different rooms tied together both by the powerline and by the common CATV cable: To avoid unnecessary clutter, only draw in the connections capable of passing ground loops. Specifically, be sure to include any and all devices which your tests have show provide electrical continuity to other, remote devices, outside of the ubiquitous powerline connection. One good way to come to terms with the situation is to make a simple block diagram of devices throughout the house which could form ground loops. Now that you have collected information about which devices in your systems are potential contributors to ground loops, you are in the position to take action to cure them. Goal: ensure that each device has zero or one (preferably one) path to earth ground. Content last modified Saturday, 9 January 2021.Įxternal links last verified Sunday, 30 January 2005.
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