Bill Crocker ...

^ I'm also considering the purchase of a PAR MON-3, omni-
^ directional, outside antenna, through Universal Radio.
^ It's optimized for 144~174, 440~470, and 800~900MHz.
^ They claim it has 1.7dBi.

A di-pole has a gain of about 2.5 dBi. Before you spend money on an expensive
antenna, try a homemade vertical di-pole with one element for each band you
want to receive soldered to some good coax. For protection from the weather
you can seal it in a suitable length of PVC pipe with endcaps.

For the bands you mention above, your elements would be: 17", 6", and 3.3".
One of each soldered to the center conductor and another of each soldered to
the shielding. This is not a transmitting antenna so no impedance matching
mechanism is necessary and the coax can run down alongside the lower half of
the di-pole.

To calculate other lengths: FEET=234/MHz (i.e. 17'=234/160.000).

Frank