Amateur radio antennas

If you want to reduce your HF vertical's ground losses but not increase its angle of radiation then you should mount your vertical on top of a 3m-4m long metal pole. Ensure the metal pole is properly grounded.
Try not to mount your vertical at, or just above, ground level!
Next, run 4 or more wire radials (these can also be used as guy wires) from just under the HF vertical down to ground level at an angle of between 20 to 50 degree angle (measured from horizontal up).
An angle of 45 degrees is best, for several technical reasons.
Next, place a circle of wire at ground level - ensuring your vertical's mounting pole is in the centre of that circle. Where the wire radials meet the ground attach those ends of each wire radial along this circle, with equal spacing. Doing so will form a skeletal conically shaped ground plane.
This arrangement reduces the need to install one or more 1/4 wavelength long (+5%, less K factor) ground plane radials per band, whilst still providing a good ground plane effect.

3. MOUNTING ON A METAL VERTICAL POLE W/ALUMINIUM RADIALS

Obtain three (3) 4m long lengths of, say 19mm diameter with 1.6mm wall thickness, aluminium tubes. Drill two closely spaced holes halfway along each tube to allow for the fitting of one U-bolt per tube.
We recommend physically strengthening each radial by inserting up to a 1m long aluminium tube (say 16mm dia. x 1.6mm thick) inside each tube, centred within the 19mm dia. aluminium tubes, before drilling. 
Fit one U-bolt at this halfway point along each tube, ensuring each U-bolt will clamp around the vertical antenna's supporting metal pole. 
Next, loosely clamp all three tubes to the mounting pole, just underneath the vertical antenna's mounting point.
Splay the tubes out evenly (60 degrees apart), then tighten all three U-bolts. This arrangement will create six (6) 2m long radials spaced 60 degrees apart.
To enhance the ground plane effect, simply clamp multi-stranded wire from one radial's tip to the next radial's tip, thereby forming a circle. The ground plane assembly will then look similar to a "wagon wheel" (or skeletal ground plane) when viewed from above or below.
This assembly approximates the effective ground plane found in average suburban areas. Commercially manufactured multiband HF verticals are tuned for operation in average ground reflectivity areas.

4. If you want to adjust the height of your multiband vertical to the optimum height then you should use a telescoping tubing mast. Many amateurs have found that it's best to test the antenna at every 50cm level of height (or at least every metre) when the antenna is mounted on top of a metal ground plane (e.g. a roof). Check the resonant frequency (which is often the point of lowest swr) on every operational band and also check the antenna's receiving performance. A beacon is usually a good indicator, as most beacons are constantly transmitting.

The higher a vertical is mounted above a ground plane, the lower will be the effective angle of radiation. The higher the frequency, the higher the antenna should be mounted, in order to achieve a lower angle of radiation. You should record signal levels daily on all the operational bands of the antenna, noting signal peaks on those bands at different antenna heights!  

Check the antenna's receiving performance on each band over several days before making subsequent height adjustments. About 2.5~3m in height is best for average length 80~10m verticals (6~8m long) and 3.5~4m for longer (9m+ long) 80~10m verticals when mounted above a good sized metal ground plane, such as a metal house roof, carport or garage.
Thanks to Phil Haig for the above "optimum antenna height" info!