Hi, Mike You've reminded me that I have pair of 2 amp FS RF ammeters (1950s/1960s era) that I need to hunt up and squirrel away before clearing out the junk around my home and preparing to move out. Someday, I may be able to put up another 160 antenna!
73, Charlie, K4OTV -----Original Message----- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Mike Waters Sent: Friday, September 20, 2013 11:42 AM To: topband Subject: Re: Topband: elevated radials Hello Jim, Thank you for this. I don't doubt for a second that my elevated 1/4 wave radial currents may be unequal. I should throw together an RF current meter and check them sometime, and add more radials while I'm at it. After the ticks and chiggers here die, though. :-) I don't have any Communications Quarterly issues, but K5IU's article sounds interesting, if anyone has a copy. 73, Mike www.w0btu.com ** > Hey Mike > > Saw your post to TB reflector: > > "I suppose if you made the elevated radials long, then you could adjust > the current balance with series variable capacitors. You could use a simple > clamp-on meter like W8JI has on his site to measure the relative current, > perhaps.I didn't bother with that myself, I was just careful to keep the > radial lengths the same length and height." > > My old friend K5IU had an article "Optimum Elevated Radial Vertical > Antennas" in Communication Quarterly, Spring 1997, pp 9 - 27. He showed > why 1/4 wave elevated radials are the worst length as it invariably results > in radials having unequal currents (at least on the low bands where the > height is small in terms of lambda). He only concluded the pattern was > distorted, explicitly stating no opinion on efficiency. Dick is pretty > careful - he likes actual measurements. The fix was to use non-1/4 wave > radials with a single lumped reactance between the shield and the junction > of all the radials to bring to resonance. Using separate reactors for each > radial makes it too critical to adjust. > > Since some of his measurements showed next to no current in some radials, > I figured right off the efficiency would almost always be higher with equal > currents, even when using shorter radials of the same number. I never > needed to use elevated radials, so it was all merely academic for me. > > I'll bet anything you have very unequal currents in your elevated radials > despite their being precisely the same physical length. Dick's article > shows how he measured the currents with a simple HB device. Don't know if > it is simpler than W8JI's or not. > _________________ Topband Reflector _________________ Topband Reflector