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Highly Shielded Audio Cable
dave wrote: The Phone Company doesn't use shielded cable for baseband audio. No, but they use twisted pair and they can still pick up a lot of RF. I've seen over 5 volts of RF on phone lines at AM radio stations that were wired with 'station wire' instead of twisted pair. The radio station audio was louder than either party on the line could talk. The fix was to rip out everything, run 25 pair twisted cable to localized terminals and use short runs to the phones. There was still some common mode RF, but at least the lines were usable since it no longer caused the volume limiter to go into continuous conduction. -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge. |
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Highly Shielded Audio Cable
On Thu, 13 Mar 2014, Michael A. Terrell wrote:
dave wrote: The Phone Company doesn't use shielded cable for baseband audio. No, but they use twisted pair and they can still pick up a lot of RF. I've seen over 5 volts of RF on phone lines at AM radio stations that were wired with 'station wire' instead of twisted pair. The radio station audio was louder than either party on the line could talk. The fix was to rip out everything, run 25 pair twisted cable to localized terminals and use short runs to the phones. There was still some common mode RF, but at least the lines were usable since it no longer caused the volume limiter to go into continuous conduction. Yes, and even in the days of the no real electronics in the phones, there were tips in the books about keeping RF out of the phones. The issue becomes more significant when all the phones are made of electronics, and there's a lot more that can act ad diodes to detect the signals. Michael |
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