Improved airborne HF receive antenna: An ILIR report

An investigation of improvement of signal-to-noise ratio in an Airborne High Frequency Single Sideband (HF SSB) system by use of an "active', dedicated, receive antenna function, in addition to a combination transmit/receive mode now commonly provided (shorted-loop). The approach described is an optional receive mode of the shorted-loop antenna, where electronic tuning, a stage of RF gain and a stage of matching is provided in lieu of passive tuned function normally provided by the HF SSB amp/coupler. The results obtained in this study show a possible improvement of 5 to 10 dB in the signal-to-noise ratio over the passively tuned antenna. This translates in raising an intelligibility reading of a 2 to 5. It is anticipated that this improved sensitivity can provide a doubling of the width of the "window' in some cases. A second advantage is to permit very rapid scanning over a broad range of frequencies within a portion of the 2-30 MHz HF Band while using a "High Q' device. The present shorted-loop design is passively tuned by cumbersome mechanically driven capacitors, thus preventing a rapid receive scan mode.