![]() If in doubt, call a licensed electrician and/or your cable TV company. A CATV isolator should not be used as a band-aid to cover up a potentially dangerous situation caused by improper or failed grounding of your CATV line or your house electrical system (I once saw a difference of 50 VAC due to a failed cable TV ground!). It only takes a small difference in potential to cause hum in your audio system, but if the difference is more than a few volts, I suggest finding the root of the problem. I suggest checking the AC voltage difference between your cable TV ground and power line ground before adding the isolator. For those who can't build one themselves, Jensen Transformers offers an excellent capacitive isolator, VRD-1FF ( It's actually the only product Jensen makes that isn't a transformer. That way, your A/V system is also isolated from your cable modem. Insert the isolator between the cable TV outlet in your A/V room and your CATV or DVR box. A 630 VDC / 400 VAC version is also available, Digi-Key #495-1318-ND. I used Epcos metallized polypropylene, Digi-Key #495-1279-ND. The capacitors should be film types with a rating of 250 VDC / 140 VAC, in countries where the line voltage is nominally 120 VAC. The F-connectors and capacitors can be housed in a small plastic project box, such as a Hammond 1591L, Digi-Key #HM100-ND. When terminated with a 75-ohm load, the isolator provides a low-loss signal path in the RF region while appearing very high-Z at the line frequency and the low-order harmonics likely to cause buzz. All you need are a pair of 2.2nF capacitors - one in the signal line and one in the ground line. Reader Gary Galo came up with a better solution, one that does not come with such a price to pay.ĬATV grounding can be a menace to audio systems and, as you point out, isolation transformers can be a problematic solution due to the losses involved.Ī better solution is to use a capacitive isolator. Most CATV isolation transformers have a price to pay because of their limited bandwidth: poorer picture quality for higher speed HD signals. I typically recommend a CATV isolation transformer but I also make that suggestion with a cautionary note. Remedying it at the source is the best way to solve the problem. If you have satellite TV like Direct it's not a problem, but if you're connected to the cable and that is connected in your system at any point, chances are good you have a ground loop. Using Molex patented technologies, very wide band devices can be achieved in relatively small packages.I mentioned one of the biggest offenders of hum creation in our systems through a ground loop comes from the cable TV connection. Customers would like to combine multiple bands in order to have a more flexible radio system. New radio designs actively require very wide bandwidth devices in a single radio. Proper design through the application of Molex expertise, along with optimized selection of materials and dimensions, results in acceptable IMD and harmonics performance with proper frequency bandwidth to meet customer expectations. Low IMD usually requires larger isolators and circulators and thicker dimensions. Low IMD is very important in systems and are not easily achieved in smaller devices. Molex engineers select raw materials with appropriate properties, including the required operating temperature range. Using high power increases temperature and, therefore, degrades performance. Power handling is very dependent on the circulator’s mechanical design and ferrite material properties. ![]() Combining our experience with our patented technologies, Molex can provide isolators and circulators as small as 6mm while meeting customer requirements. It is very challenging to meet required specifications such as those pertaining to insertion loss, return loss, power, IMD (passive intermodulation) and temperature stability in a small isolator and circulator package. Molex has invested in the development of high-efficiency, flexible automated manufacturing equipment to produce high-production-volume isolators and circulators. It requires very special customized equipment with significant investment. Automation equipment for isolators and circulators is not common. ![]()
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