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Feedline
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by KC0LTV on April 26, 2004
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Although I live in what would be considered a rural location by most (5 acre lot, fair distance to nearest neighbors), there is a very high noise level within my house. I've tried the usual culprits (computers, flourescents, etc.) to no avail. I think the noise problem may be caused by leaky electrical wiring. The noise level outside my house, at least about 20-40 ft away from the exterior with a random wire antenna is very quiet. I've never used an antenna not directly connected to the radio, but have ordered an Alpha-Delta DXLB Plus (for HF/SWL use) and TS-2000. If the antenna is 50' from the house's exterior, but the radio is in my room, near my computer, will I still experience serious interference problems? My monitor is noisy, but if I have the antenna at such a distance, will it still make too much of a difference, when connected to an interface? What's the best way of keeping RF from leaking in to the connections? What kind of feedline do you suggest?
Sorry if I've asked too many questions. Thanks and 73's to all.
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RE: Feedline
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by WB2WIK on April 26, 2004
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On HF (below 30 MHz), most reasonable lengths of coaxial cable won't have much loss; so, the selection of line is more dependent on how much power you plan to run, how long you'd like it to last, its exposure to the elements (including sunlight, which is damaging to almost anything containing plastics -- including coax), stuff like that.
In your particular case, the only difference between one cable and another is likely to be how well shielded that cable is. Double-shielded (and more) cables provide lower "leakage" (transmission/reception of signals through the shielding); however, single-shielded cable that's any good is usually very sufficient for about 99% of all amateur radio HF work, where the antenna will radiate and receive far more than the cable ever could. As such, "distance" between your antenna and sources of interference like PCs, monitors or whatever, is a prime objective in an HF antenna installation -- the farther, the better!
It's true that ham gear is not 100% shielded, and doesn't have to be, usually. Some small amount of signal can "leak" directly into your receiver through its case. Usually, that is far less than the amount of signal that will come down the transmission line from the antenna, so it's easy to ignore. But not always, especially if you have strong noise sources right there in the ham shack, along with the radio equipment.
Adding more shielding to commercial ham gear like the TS-2000 isn't so easy. It would be easier to try to separate it from interference sources; use RF filtering devices (like snap-on ferrite cores, sometimes lots of them!) on the power supply leads; and attenuate interference at its sources by using shielded, filtered cables to interconnect monitors, keyboards and such.
Anyway, I wouldn't worry about it until you have everything installed. And remember, "far away" is better than "close" when it comes to selecting antenna location. If you have acres of property to deal with, you shouldn't have any trouble installing your new wire antenna a couple of hundred feet from the house -- and get it as high above ground as possible, too. That not only helps the antennas work better, but adds more distance between the antennas and source of interference and noise located within your home.
WB2WIK/6
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