Strictly speaking a monopole isn't a complete antenna, cause it's properties depend on the connected ground or "counterweight". An ideal monople as known from antenna literature uses an infinite ground plane, unfortunately you don't have it in a portable application. A portable "monopole" must be analyzed as an asymmetric dipole to derive meaningful parameters for frequency characteristic, radiation diagram and antenna impedance. In measurements, you have to take special precautions to reduce the cable effect, otherwise you get useless results.