R&D Report 1989-07 : Use of an HF active monitoring array in the presence of high level interference. K.L. Beeke An electronically-steerable, active receiving array for HF was developed at BBC Research Department a few years ago. An investigation has now been carried out to find the limiting operating conditions for the array, i.e. under what maximum levels of interference it can be operated satisfactorily. Typically, it has been found that if interference levels are greater than about 100 dBmicroV/m, then some form of screening will be required, especially if the wanted signal level is very low and on a frequency close to an intermodulation product of the interfering signals.