| 摘要 |
<p>HIGH STABILITY MODULATOR FOR INSTRUMENT LANDING SYSTEMS In an instrument landing system for aircraft, the transmitter is required to produce an amplitude modulated signal comprising a carrier wave having sidebands containing the sum of a 90 Hz and a 150 Hz signal as modulation, and to also produce a double sideband, suppressed carrier signal in which the modulation is the difference between the 90 Hz and 150 Hz signals. In the present invention, the 90 Hz and 150 Hz signals are summed to provide a composite modulating signal that is employed to directly modulate the radio frequency carrier. To provide the double sideband signal the carrier is fed to a 180.degree. phase shift network, and the carrier and the network output are alternately delivered to a modulated amplifier stage by an RF switch which is operated with each change in the sign of a difference signal derived from the 90 Hz and 150 Hz signals. Accordingly, the output from the RF switch is a phasechanging carrier that undergoes a phase reversal with each change in the polarity of the difference signal. This phase-changing carrier is modulated with a modulating signal that is the absolute value of the difference signal, and the resultant is the desired double sideband, suppressed carrier output. A high gain operational amplifier in conjunction with an envelope detector in a negative feedback loop is employed with both the AM and the DSB modulators to insure high stability.</p> |
