More wireless questions

Hi All,
In my quest for a remotely controlled RF video surveillance robot, I've managed to acquire a pair of wireless transceivers as a donation to the
project. They are the parallax units http://www.parallax.com/detail.asp?product_id'997 part number 27997 with the little built-in whip antennas.
Parallax's advertised range is about 150 feet line of sight. According to the datasheet for the parts (which are made by linx technologies) the range can be 300 feet or more line of sight.
My reception results have been extremely poor. Electromagnetics and antenna theory are not my specialty but I've been experimenting with various lengths of wire for the transmission antenna. Just adding any old length of wire seemed to immediately improve results. I tried both 1/4 wave and 1/2 wave lengths as per the datasheet and both were about the same. I've had best results with about a 2.5 foot piece of thin wrapping wire.
Any antenna or wireless experts here that can advise on a suitable course of action to maximize reception? I'm getting a maximum of about 25 feet indoors which doesn't seem like much. Thanks in advance.
-Dave
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