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#1
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Tony Meloche wrote:
Why would reception improve - and noise drop - when the chassis ground to the receiver is removed? This is noticeable on SW, but *very* noticeable on MW. AC power in the US is at an extremely low frequency of 60 Hz, which has a wavelength of around 5000 kilometers! This means it takes a 5000 km long length of wire before you see just one full cycle. 360 degrees in 5000000 meters, or about 0.000072 degrees of phase shift per meter! The voltage at all points along a 10 meter length of wire at 60 Hz is for all intents and purposes, exactly the same at both ends, and it's an excellent ground. Not so at 10 Mhz (10,000,000 Hz), where the wavelength is just 30 meters. You'll see a whole RF wave across only 30 meters of wire. 360 degrees in 30 meters is 12 degrees per meter of phase shift. That means the voltage and current at each end of the wire will be significantly different, and it's NOT an excellent ground. In fact, it's more like a 1/3 wavelength antenna that's grounded on one end, than an RF ground. **** poor ground, it is. You didn't mention whether you live on the ground floor. If not, you're already doomed for having a good quality electrical ground at *RF* frequencies. Also, your results are poor with the ground, probably because AC power system noise is coming in through your ground wire. At RF frequencies, an AC power ground may be very poor, because a length of wire becomes an antenna, even if one end is grounded. Once you have 20 or 30 feet of wire before it goes to an actual earth ground, I think all bets are off. The best ground for an antenna system is probably the shortest and most direct to earth, independent of and as far away from noisy wiring as possible. In this case, it would be better to ground the antenna and feed your signal in via coax cable, than attempt to ground the receiver chassis. (Unless it's an old tube radio with a screw terminal for the ground. These may provide a measure of electrical safety. But otherwise... avoid.) Ground connection is to faceplate screw of a (verified) grounded 3-prong outlet, the best grouond I can muster, at the moment. Should I try a simple length of "counterpoise" wire as a ground? Given how noisy AC wiring can be, it can't hurt to experiment. Try running the counterpoise wire so it's as low to the ground (or floor) as possible. It may well outperform your AC "ground", which probably is feeding in massive amounts of electrical noise directly into your radio. If it turns out to work better one way over another, don't argue with results. :-) This, of course, is all my opinion. Please accept it as such. -- Ross Tony ----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeed.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =--- |
#2
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Ross:
I really appreciate your response to this (now aging) post, and the final result was that I ran a ground wire a total of 30" long to a galvanized steel rod sunk 6' in the the ground right outside my ground floor window. Problem solved. It is most noticeable on MW, where it is *much* quieter. Again, appreciate your response. Tony ----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeed.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =--- |
#3
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Ross I agree 100 percent with your suggestion to experiment. I installed a
12-gauge wire directly from my receiver down to a 6-foot ground rod. Total length of ground wire about 8 feet. At the low end of the receiver, around 100kHz, the ground is a definite improvement. At the high end near 30MHz it actually introduces more noise. My solution was to put a switch in the ground wire near the receiver. When I do a major frequency change I simply flip the switch back and forth for the best position and, as you said, not argue with the results. When I'm not using the receiver I leave the ground hooked up, it makes for a nice static discharge path. Al KA5JGV "Ross Archer" wrote in message ... Given how noisy AC wiring can be, it can't hurt to experiment. Try running the counterpoise wire so it's as low to the ground (or floor) as possible. It may well outperform your AC "ground", which probably is feeding in massive amounts of electrical noise directly into your radio. If it turns out to work better one way over another, don't argue with results. :-) -- Ross |
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