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Richard Clark wrote in
: On Sat, 02 Jan 2010 13:21:03 -0600, Lostgallifreyan wrote: Well, my plan is to use a ground at the antenna end, right underneath it. This bodes ill if you do not tie that ground directly to the service ground. Further, a "ground" as you describe it (incompletely) sounds suspiciously like a ground rod. This is NOT the same thing as RF ground - not even close unless you live within several meters of low tide along a major ocean shore. I'll get a good 4' ground rod and rig up an 18' vertical whip as I learned of in details I posted about earlier. Suspicions confirmed.... I understand that good reception depends on a good compromise between selectivity and sensitivity, and no doubt the antenna 'tuner' helps with that, though I'll mainly be concerned with good ground and local common mode noise rejection. This does not acknowledge the significance of INTERMOD problems. Experience may have to teach that (when you make all these improvements and have poor results for your effort). My first attempt at the line between antenna and receiver will be a balanced line with a toroid at each end for current isolation This is a very, very curious novelty. You do not describe a "balanced" system with a ground rod and vertical, so any effort at "balanced" lines is window dressing only. The reason for placing "balanced" within quotes is due to the inordinate care and skill required in obtaining a balanced design. It is more often achieved with coax. Too often, "balanced line" is approached with the mysticism of universal relief for whatever ails a listener. and possibly the suggested Norton preamp on the receiver input, I must have missed that posting. Sounds like another elaboration. but I'll try without it first as I suspect I'll get enough signal strength to satisfy me for a while. If I have to use coax I will but I'll try the easier options first. This basic plan does involve a 10:1 ratio in windings on the far end toroid which should help smooth out peaks of resonance as described by John Doty and others as mentioned before, and if nothing else, drives a stronger current in the balanced line part of the system. This is the doohickey I spoke of. It is basically the refuge accessory of the lowfers where the span of frequencies is, maybe, three to one and not like the ten to one of HF SWLing. I'm no longer much concerned about matching impedances, but I will be watching for results of changing antenna length if resonance seems to be an issue. This is at cross purposes. You don't have many realistic options of changing antenna length (height) as you do with a simple tuner when it comes to matching. My interest in the 'doohickey' or any other widget was mainly in what appeared to be a means of reducing the difference in signal strength extremes due to resonance. I understand that if I subsequently have to select the weaker of two close stations I'll either have to add some 'trap' for a specific offender, such as a trimmed lengh of unterminated coax (though as far as I know, that trick is usually reserved for much higher frequencies), or use a manually tuned system which I'll explore if it becomes a dominant concern. Traps don't work very well for adjacent AM/SSB stations, you need cascade XTAL ladders to do that. Tuners, also, can only operate within the combination of number of reactive elements and Q. Please respond to your perception of the problem of INTERMOD as it is, as I said, the silent killer of reception. 73's Richard Clark, KB7QHC I haven't a clue about intermod, yet. One thing at a time. Right now I see at least three contradictions (re ground rods, transformers, and feedlines) with advice from several people, one of which (the guy who wrote the description of the antenna and balanced line I mentioned) is part of a group of hams who is turned to for advice by the others. No guarantee of correctness, perhaps, but if I keep on being told I'm wrong when my stuff is coming as directly as I can get it from others with experience, then as far as I'm concerned I'll do what I think best and get out of the crossfire. Specifically, many times I've seen advice that service grounds are not adequate because of common mode noise and local currents, hence the ground rod you vehemently negate. I can ground to service ground at near end but if the receiver is on batteries, not connected to anything except a transformer coupling RF from the antenna, then the ground only needs to be at the antenna end, according to advice I've seen in several places. Even if I do ground to a water pipe or other local ground, all advice I see until now insists on having a ground rod as close to the antenna as possible, no matter what else I do, yet now you urge against this. I will stop asking for advice if all I see is vigorous contradiction between people who claim knowledge I do not have. Diverting that disagreement to one with me doesn't alter this, I did not originate the info behind the choices I am considering. Even if all the various contributors come here and duke it out between them it appears I'll be none the wiser. |
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