Before buying another antenna try this. Add a 'tail' to your present rubber-duck antenna. Basically a 1/4 wave section of insulated wire connected to the "ground" of the antenna or the radio chassis at the antenna. The typical HT uses the radio's chassis, the operators hand, and whatever is close to supply that 'other half' of the antenna. That 'tail' means providing a half way decent "ground" instead of the 'kloodged' up arrangement that's normally provided. Might cost you all of 20 cents, maybe? I have one of the Wouxuns and this does work. It certainly won't provide a 'decent' antenna system, but it's 'better' than what's normally provided.
If you want to use that HT in a vehicle, the best bet is to use a mobile antenna. That opens up several possibilities. Most of those possibilities will definitely be 'better' than a typical rubber-duck antenna.
Most antenna 'adaptors' do have some loss, but not as much as you might think. Most losses of that sort really are not very important, negligible when comparing the results of an external antenna to the typical 'duck'. The local Radio Shack has an SMA adaptor to an SO-239 using a short section of something like RG-174. That relieves some of the stress of a larger type of coax being directly connected to an HT. (The key word in that is 'short'!) Still more losses? Yep, but the end results are still better than the included 'duck' antenna with most HT's.
The biggest differences between an HT and a mobile radio is power output. If both are limited to the same power output, then the differences are less (but still there). An HT does have a useful purpose, but it's more about convenience/cost than ability, and the liabilities usually out weight the 'pluses' when any significant distances are involved.
- 'Doc