  Over the past years, the freely available Monte Carlo-code REAS which
simulates radio emission from air showers based on the geosynchrotron model,
was used regularly for comparisons with data. However, it emerged that in the
previous version of the code, emission due to the variation of the number of
charged particles within an air shower was not taken into account. In the
following article, we show the implementation of these emission contributions
in REAS3 by the inclusion of ``end-point contributions'' and discuss the
changes on the predictions of REAS obtained by this revision. The basis for
describing radiation processes is an universal description which is gained by
the use of the end-point formulation. Hence, not only pure geomagnetic
radiation is simulated with REAS3 but also radiation due to the variation of
the net charge excess in the air shower, independent of the Earth's magnetic
field. Furthermore, we present a comparison of lateral distributions of LOPES
data with REAS3-simulated distributions. The comparison shows a good argeement
between both, data and REAS3 simulations.
