GB817696A - Circuit for selecting both upper and lower sidebands - Google Patents

Abstract

817,696. Radio transmitting systems. COL. LINS RADIO CO. Dec. 19, 1956 [April 12, 1956], No. 38719/56. Class 40 (5). In a single sideband transmission system in which the signals are modulated on to a subcarrier and one sideband is selected, this sideband is selectively transmitted as either the upper or the lower sideband of a carrier having a frequency n + 1 times the sub-carrier by mixing the single sideband signal with a second subcarrier which is switched so as to have either a frequency n times the first sub-carrier or n + 2 times the first sub-carrier and then selecting the desired band by a filter centred on a frequency n + 1 times the first sub-carrier. The audio signal e.g. 1 kc/s., is combined in a balanced modulator 6 with a 250 kc/s. sub-carrier generated at 7. A mechanical filter 8 selects the resulting upper sideband (251 kc/s.) and this is applied to a second mixer 14. Also applied to the second mixer 14 is the 250 kc/s. sub-carrier which has been multiplied either by 2 or by 4. The multiplication factor is selected by a switch 10. If the sub-carrier is multiplied by 2 the output of the mixer 14 includes a 751 kc/s. (upper sideband) signal, and if the sub-carrier is multiplied by 4 the output of the mixer 14 includes a 749 kc/s. (lower sideband) signal. These signals are selected by a band-pass filter 11 centred on 750 kc/s. The output of filter 11 is modulated on to a main carrier at 15.