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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Diy ground loop isolator for cable box?? posted by Frank25 on January 31, 2007 at 08:01:11:
See:
http://www.AudioAsylum.com/audio/tweaks/messages/15453.htmland my comments on the observation that this arrangement is unshielded, and has limited RF bandwidth:
While use of any such transformer balun brands/models at random MAY cause some shielding loss, if the two specific RS part numbers I suggest are used, there should be little problem.Dozens of people have bothered to e-mail me and relate their success in removing cable TV hum related problems, only one fellow had problems with the picture, and it turned out he was using his for a satellite run of cable, and the super high RF frequencies were the problem, as such cable band baluns are not designed to handle the satellite frequencies.
Having worked for a video company for a time, I have experience with both RF video and composite video signals and their needs and foibles. I tested these back to back baluns on test gear, and while they do droop a bit at the very high end of the cable bands, the performance is more than adequate for all but the worst situations (end of the block feed, the high end of the band is already down significantly, etc.)
If there IS interference, then as the other fellow found out, you can shield the assembly with alumunum foil. The way to do this so it is is not intermittent, is to wrap electrical tape on both the 300 ohm leads, and then put a piece of the foil (HD type works best)over the leads, and then wrap the foil around the leads and the body of one or the other of the 75 ohm ground shells. You could even possibly tuck the foil under the edge of the push on shell, so it is trapped between the ground shell and the threaded F-connector on the gear.
If spending just a few bucks and playing with some foil has you concerned, then you can always pay the $50 to $100 for the premium gold-plated die-cast shielded box isolation transformers with bandwidth from near DC to light. Yes, they WILL work well, and isolate, and remain sufficiently shielded.
Jensen makes them, and the Audio Amatuer Corp. sells them:
CATV model PJ-VR1FF for $50, and the component/composite model PJ-VB1BB for $100. 1-888-924-9465 or try Http://www.audioXpress.com/
(No I do not endorse these, but Jensen is known for their quality in audio transformers, so I would think these are a safe bet.)Mondial also offers one for $100 the MAGIC model., available through Audio Advisor. 1-800-942-0220 and they have a website.
Places such as Parts Express and MCM might have cheaper models, but they are very likly to be what I have described above in a box, for way more. At least the above mentioned premium units use very high quality transformers, and have matching high performance specs.
END COMMENTS
Note that RS may no longer carry these exact part numbers.The 15-1253 looks like this:
http://www.radioshack.com/sm-see-all-needs-and-wants--pi-2062054.htmlThe 15-1140 looks like this:
http://www.radioshack.com/sm-indoor-outdoor-matching-transformer--pi-2103912.htmlAlso note that you can connect two of the #15-1140 type units back-to-back, this will give you a set of male F connectors to plug into, while using the 15-1253 and the 15-1140 will provide a M and F set of connections, more suitable for a "thru" connection.
When I measured the loss thru the M/F pair, it was less than 1 dB in the middle of the CATV RF band, with slightly higher losses at the high end of the band.
Jon Risch
Jon Risch
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Follow Ups
- Of course. - Jon Risch 19:00:01 01/31/07 (0)
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