GB1132545A - Improvements in and relating to apparatus for frequency conversion of radio signals - Google Patents

Abstract

1,132,545. Frequency changers; single sideband modulation; radio signalling. HUGHES AIRCRAFT CO. 13 Jan., 1967 [28 Jan., 1966], No. 1980/67. Headings H3B, H3R and H4L. In order to translate en masse a plurality of signals having frequency components within a given band of frequencies to higher frequencies pumped varactor diodes are disposed in the conjugate arms of a hybrid network and voltages having opposite phase which correspond to the signals to be translated are impressed across the diodes. The apparatus may be employed in a station apparatus, Fig. 3 (not shown), and Fig. 4, for translating television and FM signals in a particular band to the microwave region for further transmission. A single broadband or multiple narrow band antenna is/are connected to a hybrid 32 of an up-converter. Wave energy corresponding to the input signals at arm 33 is divided by network 32 and transmitted to arms 35, 36 with a phase difference of 180 degrees and thence to reverse biased varactor diodes 47, 48 and 50, 51 connected in conjugate arms 46, 49 of a second hybrid network 44 via impedance matching transformers 52, 54 and inductances 53, 55. Microwave pumping energy is applied to arm 45 of hybrid network 44 where it is divided before propagating in arms 46, 47 to the diodes where the energy is reflected by an amount dependent upon the effected impedance presented by the diodes determined by the modulating potential applied thereto from arms 35, 36. The reflected wave energy from the diodes comprises a carrier signal at the pump frequency and amplitude modulation components in the upper and lower sidebands and the magic-T hybrid 44 is constructed so that the frequencies in the lower sideband are below cut-off and since the components at the pumping frequency are reflected in phase they are not coupled out of arm 56. Since the modulating potentials applied to the diodes are 180 degrees out of phase the reflected energy in the upper sideband will also be out of phase and the two components of the modulated upper side band will recombine and be transmitted out of arm 56. A filter may be connected between arm 56 and a microwave amplifier, the amplified output of which is fed to a transmitting antenna. In the arrangement of Fig. 5 (not shown), and Fig. 6, which is a cross-section of one conjugate arm of a hybrid magic-T 44 of Fig. 5, only one diode 72 is used in each arm. The impedance matching transformer 54 comprises a coaxial line section disposed above the upper broad wall of arm 49 and the modulating input signals are applied thereto via coaxial connector 63. Biasing current is applied to lead 88. A low-pass filter section formed by conductive wire 81 and conductive spacers 83, 84 prevents pumping frequency or sidebands from entering the modulating circuit. A second low-pass filter comprising conductive wire 92 and conductive spacers 94, 95 prevents microwave energy from entering the D.C. biasing circuit and a third filter section formed by coil 90 and a bypass capacitor formed by lead 88 passing through end plate 86 prevents the low frequency modulating current from entering the D.C. bias circuit.