Another BPL Trial Dropped > Underground lines?

Underground lines?

said by panth1:

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I keep seeing these trials in areas with overhead service. Have there been any trials using developments that have underground service and would that make a difference?

Feed the lines at the point they go underground where they are shielded.

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reply to panth1
There is aprox. -3db effect in signal strength between above ground wiring and below ground, depending on frequency used of course. BPL whether above or below ground uses HF frequencies from around 1Mhz all the way up to 100Mhz. This is shown in the ARRL archives on BPL. So if you were experiencing +15db over S9 interference with above ground system, the same system with below ground would still be S9 +12db. Now even with below ground systems, the wiring comes up into the buildings walls and ceilings anyway so then walla you have another +3db from that building anyway, depending on how far the buildings are spaced would determine the average strength somewhere between +12db over S9 to +15db over S9 in that area. The frequency used is important here because of wavelength. The longer the wavelength the farther the interference will travel whether above or below ground. Example a signal at 7Mhz has a wavelength of aprox. 132Ft per cycle. If the system were below ground for 60 ft. and then came up into the building, that leaves 1/2 wavelength for above ground radiation - and very effective radiation at that. About the only way to contain this interference signal is to go coaxial. Now the cable co. has already done this and very well. They adhere to strict guidelines as far as leakages, and come out and fix any leakages very quickly. Will the power co's come out and fix your baby monitors when all you can hear is static? Will they come out and fix your garage door opener when it opens and closes without command from you? Heck No - but they won't tell you this.

I forgot to mention in the above post that the wavelength stuff is assuming conducted noise not actual radiated. The radiated part is affected by many other factors. Also the cable co. that uses coaxial cable for all their stuff, they also use frequencies well above HF 1-30Mhz, it's more like mid to high UHF band 400-500Mhz.

The cable system down stream is in the 400-500MHz range or even up to 750MHz. The return path is in the range of 5-50MHz. But since cable is a shielded system it does not matter much.
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