Abstract: A portable tester for local area networks comprising a AUI circuit coupled to a media specific transceiver, a battery, a push-to-test switch and four light emitting diodes and an RJ45 jack for each of a personal computer and a network hub. When the push-to-test switch is pushed, power is applied to the media access unit and a link pulse is generated for coupling via a PC jack to a personal computer plugged into that jack. The link pulse is also coupled to any network hub plugged into a hub jack. The PC and network hub cannot both be simultaneously connected. If whichever unit is connected receives the link pulse and generates its own link pulse which is received by the tester, a link status LED is lit green. Otherwise, it is left dark. If the unit connected outputs a data packet in response to receipt of the link pulse, a receive data LED is lit green. Otherwise, it is left dark. If the link pulse is positive-going on the correct line, a polarity LED is lit green. Otherwise, it is left dark.