The trick is trivial, and is surely well known to all hams operating in HF: a quarter wave vertical MUST be used with a good ground plane or against one or several counterpoises. This is true also in VHF region, but what is the amount of improvement? I soon arrange a quick-and-dirty counterpoise for my VX-2: 49 cm of speaker wire wrapped around the SMA antenna connector: the improvement in RX seems to be incredible, better than 1 s-point, in some conditions even 2 s-points!
The performance improvement is significant: we can note that 1 s-point is 6 dB; this means that my VX-2 with quarter wave counterpoise is more powerful that a 5W HT without counterpoise. In TX same situation: other hams reports that is a +1 s-point when I use the counterpoise.
I’ve built a more clean and stable version: a 6mm ring terminal and 49 cm of RG-174 (only braid connected). The 6mm terminal fits well in the SMA connector, and screwing the antenna lock counterpoise firmly in place.
The counterpoise is useful for all kind of quarter wave antenna, even shorted quarter wave or rubber ducks. Of course, I try also many conventional 5W HT, with the same (good) results in terms of performances. In UHF the improvement is less noticeable with my telescopic antenna, which is a half wave on 70cm.
This simple trick really performs well, is very cheap and fast to build. I’m surprised that is unknown by most ham radio operators. Try it!