I hope people with experiance of dual band antennas can comment on that.
I put up a Diamond X510 today and it's a huge improvement.
It's about the same as my best antennas in the 700-900MHz range when looking at signal levels from cellphone systems. I don't have any radiossystems in that range.
In all other lower frequency bands the $130 dualband X510 are way better than tuned GP's and moderatly directional gain antennas.
I tested 118-145-170-390-420-470MHz and I have no doubt that a smaller $100 Diamond X300 will easily outperform any dipole type antenna like a ST-2 or a discone at any frequency range.
The $65 Diamond X50 might also work but it has a low gain of 2dBd in VHF and 5dBd in UHF and of course less than that outside of the amateur frequencies.
/Ubbe