Changing the angle of the radials will change the impedance slightly. Running them 90 deg to the vertical element will be slightly lower impedance than bending them down which will raise the impedance. However, you can trim the vertical element to get a perfect match either way.
A 1/4 wave whip over an infinite size perfectly conducting ground is supposed to have an impedance around 35 ohms. As you lessen the size of the ground plane from a huge copper sheet to say three 1/4 wavelength radials, the impedance will be higher than 35 ohms and closer to 50 ohms.
If you shorten the whip slightly the resonant frequency will go up but at the same time there will be slightly less capacitance between the whip and ground causing the impedance to go up a little. Lengthening the whip will create more capacitance between the whip and ground causing the impedance to go down, so adjusting the whip can make up for minor impedance mismatch in addition to changing the resonant frequency.
prcguy
Joeyvb, you can't adjust the match by changing the angle of the radials like Wyandotte says. You can adjust it by changing the length of the vertical or radiating element. The radials form the ground plane and will not have an effect on the match as long as one of them is at least 1/4 wavelength long. They will effect the angle of radiation. Bending them down will lower the angle more toward the horizon.
