Abstract: The invention concerns a combination of a transmitter/receiver (12, 13) having a predetermined frequency/wavelength and an antenna (15), the antenna comprising a coiled wire portion (16) one end of which is connected to the output (14) of the transmitter/receiver and a straight wire portion (17) one end of which is connected in series to the other end of the coiled wire portion, the combined length of the portions being no more than one quarter wavelength, the inductive reactance of the coiled wire portion (16) being selected to both substantially tune out the capacitive reactance of the transmitter (12, 13) and the capacitive reactance of the straight wire portion so that the overall impedance of the system is predominantly resistive, and at least the majority of the coiled portion (16) being external to the conductive portion (12) of the transmitter so as to effectively add to the electrical length of at least the straight portion (17) and itself act as a radiator.

Abstract: The invention relates to small low voltage transmitters for transmitting at a single frequency, preferably in the VHF range, suitable for use in the location or tracking of birds, animals, vehicles, people or other objects where the transmitter is required to be small and light. The transmitter circuit includes an oscillator stage (61) based on a crystal oscillator XL1 having a predetermined nominal frequency, a frequency multiplying and amplifying circuit (62) arranged to double the nominal frequency and pulsing circuit (60) designed to give a pulsed output at a predetermined frequency, the pulsing stage (60) includes a pair of transistors TR11, TR12 having effective negative resistance, which transistors are separate from the transistor TR3 in the oscillating circuit and which are off during an Off Period and on during an On Period, with the Off to On period in the ratio of at least 15 to 1.