Abstract: A protection circuit for a primary battery pack provides the battery pack with reverse charge protection. The protection circuit features a metal oxide semiconductor field effect transistor (MOSFET) with a steady state source to drain voltage. The source to drain voltage is controlled through a feedback loop that includes an operational amplifier. The MOSFET is configured in series with one or more battery cells allowing current to flow from the cells and preventing current from flowing to the cells. The MOSFET provides reverse charge protection with a small forward voltage drop and a small reverse charge leakage current.

Abstract: A frequency hopping radio communications system has a plurality of radios each incorporating a transmitter and a receiver. When a radio is not transmitting or receiving, a switch switches it into a mode in which it monitors the signal strength in each of the available hop channels so as to assess the level of interference, and selects a subset of the total number of channels, those having the lowest interference level. The identities of this subset of channels are stored in a store. When the radio is to transmit a message, it first transmits the identities of the subset of channels stored in the store--using the full number of hop channels (the information being transmitted with sufficient redundancy to overcome likely interference). The receiving radios receive the identities of the subset of channels. The transmitting radio then transmits, pseudo-randomly, on this subset only and each of the receivers receives on this subset only.