Freeze circuit for aircraft radio navigation systems

• US 3,887,872 A
• Filed: 12/05/1973
• Issued: 06/03/1975
• Est. Priority Date: 12/05/1973
• Status: Expired due to Term

• Current Assignee: Claude A. Sharpe
• Original Assignee: Claude A. Sharpe
• Inventors: Sharpe, Claude A.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Blum, T. M.
• Application Number:
  US05/421,881
• Time in Patent Office: 545 Days
• Field of Search: 325/21,22,473 343/228
• US Class Current: 342/420
• CPC Class Codes: G01S 1/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: H04B 1/40 Circuits

Abstract

In aircraft, operation of on-board communications transmitter frequently interferes with radio navigation receiver. The invention provides switch means interposed between navigation receiver and course indicator or autopilot which, upon operation of transmitter, interrupts guidance signal from navigation receiver and holds input to course indicator or autopilot constant until navigation receiver has recovered from interference.

Claims

1. In a radio navigation system, means for eliminating adverse effects of false guidance signals caused by intermittent transmissions from a nearby communications transmitter, said navigation system including a receiver tuned to a frequency within a band of frequencies assigned for navigation use and providing guidance signal output, and means utilizing said guidance signal output, said communications transmitter operating in a communications band of frequencies adjacent said navigation band of frequencies and being active to transmit or inactive depending upon the operation of a first switch means;

comprising, second switch means interposed between said navigation receiver and said utilizing means, a first condition of said second switch means permitting application of guidance signal from said receiver to said utilizing means, a second condition of said second switch means interrupting application of said guidance signal to said utilizing means;

means for storing said guidance signal during the time said second switch means is in said first condition and for applying said stored guidance signal to said utilizing means as a substitute for said guidance signal during the time said second switch means is in said second condition; and

means controlled by said first switch means and controlling said second switch means to cause said second switch means to change from said first condition to said second condition whenever said transmitter is active and to revert said second switch means to said first condition whenever said transmitter is inactive.

2. The combination of claim 1 wherein said second switch means comprises a field effect transistor having an input electrode to which guidance signal from said receiver is applied, an output electrode for applying guidance signal to said utilizing means and a control electrode, said means controlling said second switch means biasing said control electrode for conduction between said input and output electrodes in said first condition and for non-conduction between said input and output electrodes in said second condition.

3. The combination of claim 2 wherein said storage means comprises a capacitor and a high input impedance amplifier, the input of said amplifier being connected to said transistor output electrode, the output of said amplifier being connected to said utilizing means, said capacitor also being connected to said transistor output electrode.