By the way, Tom A 40 m 1/4 wave over 4 elevated radials should be a really good performer. I built one that was a good match into Asia and other "faraway places" when compared to my full-size 1/2 wave 40m vertical dipole. Couldn't tell any really noticeable difference when switching back and for the between the two and doing A/B comparisons on long-haul paths. - FWIW (The base of the 40m vertical was up about 20 feet.)
73, Charlie, K4OTV -----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Charlie Cunningham Sent: Saturday, January 25, 2014 9:05 PM To: 'Tom W8JI'; [email protected] Subject: Re: Topband: Grounding the ends of radials All true, of course. Aside from the rocky condition of my lot, one of the main reasons that I rely on elevated radials is that I can model those antennas handily and I get good measurable results that compare and agree pretty well with my EZNEC models. Especially useful in parasitic or phased arrays! 73, Charlie, K4OTV -----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Tom W8JI Sent: Saturday, January 25, 2014 8:47 PM To: [email protected] Subject: Re: Topband: Grounding the ends of radials >I generally agree with you, Bob - especially with regard to not >grounding the far ends of 1/4 wave radials!! After all what we are >trying to establish is a low-impedance "image plane" for the vertical >radiator to be fed against! A 1/4 wave wire, grounded at the far end >would have a high impedance to ground at the base, or feed-point, of >the antenna! Makes no sense! Would not result in a very favorable "driving-point impedance! The issue is complicated by the number of radials, the soil, and the radial length. Even buried radials directly in contact with soil are "resonant", the extent of which depends on the shallow and deep characteristics of the earth. In most soils, bare wires are not grounded for RF as well as people probably think. Measuring buried 40 meter radials here, I could get a fairly high base impedance with some radial lengths and numbers. This did **not** affect the field strength. With about a dozen radials the base impedance of a 40M vertical with long radials was about 50-60 ohms. It had about the same measured field strength as 4 elevated resonant radials that had a base impedance down in the upper 30 ohm range. People used to use ground rods at the ends of radials when they had to truncate the radials. Also, some people used ground rods and no radials at all. They swore by those systems, wrote articles about those systems, and even bragged about all the DX they worked. Opinions, contacts, or feelings tells us more about how difficult it is to tell how well something really works than it tells us how the systems actually work. That's why this stuff rages on and on for decades. Even the AM BC stuff was mostly meaningless nonsense. People would pull radials in over other radials while guessing not many of the old radials were still there, make measurements with 3 dB of wobble in the readings and pick the numbers they liked, and call it conclusive evidence. 73 Tom _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
