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Starman:
In fact it was Doty, if I recall, who mentioned to me that you really should ground both ends of the coax. Like you, I just didn't know how to do that easily at the 'high' second story end of his coax feedline approach. In actuallity, my antenna feedline never comes down near the ground so I had to run a separate gound line (aluminum wire) down to my earth post. I split the feedline in the center and grounded the shield at the midpoint. It seems Ok (certainly better than without the ground). -- Brian Denley http://home.comcast.net/~b.denley/index.html |
#12
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STARMAN,
"I've also noticed that the noise level is much higher when I partially remove the antenna coax connector on the back of the receiver, so that only the center pin is making contact." 1. With a Primary Grounding Point at the Antenna: * If you have a separate Shack-Ground for your equipment (radios etc) you 'may' NOT Notice this Higher Noise condition when the 'outer-ring' of the PL-259 Plug is diconnected from the back of the radio/tuner/switch. * If you do NOT have a separate Shack-Ground for your equipment (radios etc) you 'may' Notice a Higher Noise condition when the 'outer-ring' of the PL-259 Plug is diconnected from the back of the radio/tuner/switch. 2. A Primary Grounding Point outside and away from the house offers many advantages for Noise Reduction and Safety. 3. A Secondary Grounding Point inside the house for the equipment offers additional advantages for Noise Reduction and Safety. 4. This informational webpage presented by "Wellbrook Communications" * LOW NOISE ANTENNA USING * THE UNIVERSAL MAGNETIC BALUN * PLUS THE ANTENNA FEEDER ISOLATOR Universal Magnetic Balun is specifically designed to reduce noise, especially mains borne, by isolating the feeder winding of the Balun matching transformer from the antenna. GoTo= http://www.wellbrook.uk.com/longwire.html Take A Look At the Diagrams On This WebPage - They Tell It All ! 5. Another Look at Noise Reducing Antenna Systems - by Mark Connelly [WA1ION] GoTo= http://members.aol.com/WA1ION/nrants.pdf Here again WA1ION uses a 9:1 Matching Transformer between the Antenna Element anf the Coax Lead-in-Line and a 'second' 1:1 Matching Transformer in the Shack between the Coax Lead-in-Line and the receiver. 6. Grounding is KEY to Good Reception - by John Doty http://www.hard-core-dx.com/nordicdx...d/ground2.html http://www.hard-core-dx.com/nordicdx...und/index.html 7. Impedance Matching Transformers for Receiving Antennas at Medium and Lower Shortwave Frequencies - by Bill Bowers, John Bryant and Nick Hall-Patch [VE7DXR] GoTo= http://radiodx.com/spdxr/media/imt_doc1.doc 8. The Purpose for a Balun - by John Doty GoTo= http://www.hard-core-dx.com/nordicdx...ed/balun3.html "The purpose of a balun is to block common mode waves (current flowing in the same direction on both conductors of a transmission line) and pass differential mode waves (current flowing in opposite directions on the conductors)." 9. The "Grounding-Point" = Ground Rods and Ground Wires ETC. GoTo= http://groups.yahoo.com/group/SWL-AM...na/message/425 iane ~ RHF .. All are WELCOME at the "Antenna Ashram" GoTo= http://groups.yahoo.com/group/SWL-AM...na/message/502 .. .. = = = starman = = = wrote in message ... Brian Denley wrote: starman wrote: I haven't found this to be so in my case. The coax shield on my low noise inverted-L is grounded only at the bottom of the antenna's single wire downlead, which is close to the ground. The coax runs about 75-ft along the ground to the house, then up one story to the receiver. There is no ground on the receiver end of the coax. The noise from home applicances is almostly completely gone now with this antenna configuration. Starman: My random wire coax feedline is also only grounded at one point (the center, oddly enough) but the fact is that for the feedline to effectively not act as part of the antenna, the shield must me grounded at BOTH ends. Is one point better than nothing? Sure. Like you, I live with it because I find it difficult to implement. I came to the conclusion that the single ground at the far end of the coax is 'effectively' preventing the shield from being a common mode antenna because the noise level is much lower than before I built the low noise 'Doty-L' antenna system. Another factor is that most of the coax is laying on the ground. This also helps to reduce common mode reception on the shield. There's about fifteen feet of coax above the ground going up to the receiver on the second story. I've also noticed that the noise level is much higher when I partially remove the antenna coax connector on the back of the receiver, so that only the center pin is making contact. |
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