the propagation loss a radio signal experiences along distances r 1 in db and the free space propagation loss l is given by the classical relation the base antennas 7 19 must be placed in the area to minimize the dynamic operating range d in the preferred embodiment the base antennas 7 19 are uni directional antennas placed high above the service area with the maximum lobe pointing down on this area thus no portable p n can get very near to the base antennas 7 19 with the base antennas placed such that the distances r 1 and r 2 are minimized l 1 is comparable to the value of l 2 making the difference between them small thus a compressed dynamic range is realized in the preferred embodiment of the system the propagation loss is simply the free space loss since all portable units will have line of sight to the base antennas in alternative embodiments the radio signals may experience other propagation losses as they travel through walls or other structures if this is the case these propagation losses need to be empirically determined and then added to the worst case loss l 2 in order to determine the dynamic operating range of the system in such instances the base antennas are placed such that the difference between l 1 and the new l 2 is minimized turning now to fig2 the portable radio 33 in.