Abstract: A receiver for locating a source of RF radiation received by a four-arm spiral antenna having an angular measurement frame normal to the antenna axis, including a detection circuit for detecting signals received from each of the spiral arms in response to receipt of RF radiation by the antenna; a first comparison circuit for comparing signals detected from a first opposite pair of the spiral arms to produce a first signal that is proportional to a first function of the frequency of the received RF radiation and the angular displacement of the radiation source in the measurement frame; a second comparison circuit for comparing signals detected from the remaining opposite pair of the spiral arms to produce a second signal that is proportional to a second function of the frequency of the received RF radiation and the angular displacement of the radiation source in the measurement frame; and a processing circuit for processing the first and second signals to produce third and fourth signals that are proportional