The antenna you're describing is a dipole. Half of the dipole is the
upper vertical wire. The lower half is the radials. Changing the length
of one half has the same general effect as changing the other half.
Roy Lewallen, W7EL
David Harmon wrote:
When making the standard VHF-UHF ground plane antenna as illustrated in
all the books, with four ground radials sloped down at a 45 degree
angle, are those radials a tuned length? How much difference would it
make if they were some random length considerably longer than specified?
(as, for example, using the antenna on a different band by merely
changing the center vertical element.)
Re: Reflexion on ground and radials ... For a given antenna height and elevation angle, it's the same distance from the antenna. ...Broadcast radials are, I think, around a half wavelength long. ... Any radiation from the center of the vertical at an angle below 26 degrees would reflect beyond the radial field, so the elevation pattern for all angles below 26 degrees would be independent of the radial field. ... (rec.radio.amateur.antenna)
Re: Quarterwave vertical with radials ... One of the earlier postings suggested that the quarterwave vertical antenna... RF experts on this newsgroup cannot agree on whether i) the radials reflect ... the wave or ii) the field from the radials cancels out. ... You can view the radials as reflecting the wave and having current induced ... (rec.radio.amateur.antenna)
Re: VHF Ground plane radials ... with four ground radials sloped down at a 45 degree ...angle, are those radials a tuned length? ... these guys are telling you that the antenna you describe is a dipole? ... If you had called it a dipole, I'd have expected the common half wave wire fed in the middle. ... (rec.radio.amateur.antenna)
Re: 80m Vertical over lossy soil ... Here, the monopole functions as a dipole but 1/2 of the radiation pattern exists as a mathematical image reflecting against true ground (not a good conductor of electrons like radials, merely a zero voltage reference point). ... Although the mathematical image seems to only exist in theory, the observed physical effects of RF transmission follows the rules of energy conservation and the antenna transmits real RF that can be measured as if it were a true vertical dipole antenna. ... Even if you could make a zero-loss connection to ground, that dirt still doesn't provide the "mathematical image" of a perfect ground plane. ... (rec.radio.amateur.antenna)
Re: Reciprocity of vertical antenna ... In transmit mode, the field from the radials cancel out. ... When the antenna is receiving, the incoming wave interacts with the radials and is reflected into the vertical element. ... the radials have a standing wave on them and provide the RF ground side by 'converting' the high voltage at open circuit end to a low voltage at base of antenna.... (rec.radio.amateur.antenna)
