In reply to G3CWI:
I personally try to test simple antenna designs in 4nec2 to get basic idea what their radiation pattern should be, how much gain I can expect and to compare antenna raddiation pattern to known antennas. I can suggest this software as it is very easy to use and you can learn it from a 15 minute video on youtube.
BUT antenna model only says what is the BEST antenna can do. This is special problem with verticals. Dipoles are good in this.
What should be considered with verticals (or any short antenna) is radiaton resistance vs. ground resistance. This two terms make the radiation loss.
radiation efficiency %] = radiation resistance [ohm] / (radiation resistance + ground resistance) [ohm]
Radiation resistance is roughly equivalent to impedance of the antenna at the feedpoint. Ground resistance is the RF resistance of ground (radial) system. Ground resistance is nearly not measurable, at least with equipment most of us have at home and should not be confused with DC ground resistance.
To show you an example, say ideal 1/4 vertical has impedance about 38 ohms. Now imagine a poorly designed radial system with one or two radials in poor soil and let’s just assume it has radiation resistance about 500 ohm.
38/(500 + 38) = 0.07 = 7% radiation efficiency
This is rather extreme example but in this case, if you used 100W, 7W will be radiated and 93W will heat the ground around antenna. Poor moles!
Now lets try the same with half wave vertical over the same ground. Common end fed half wave has impedance about 3000 ohms.
3000/(500 + 3000) = 0.85 = 85% radiation efficiency
Conclusion from this is that low dipole can easily outperform a vertical if impropper radial system is used. This applies especially to very short verticals where radiation resistance can drop below 10 ohm easily.