Amplifiers – Combined with automatic amplifier disabling switch means
Reexamination Certificate
2000-04-07
2001-09-25
Pascal, Robert (Department: 2817)
Amplifiers
Combined with automatic amplifier disabling switch means
C330S12400D, C330S12400D, C330S165000
Reexamination Certificate
active
06294955
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to the art of radio broadcasting and, more particularly, to disconnecting and/or replacing one of a plurality of power amplifiers in a transmitter while the transmitter is operating.
2. Description of the Prior Art
The U.S. Pat. Nos. to H. I. Swanson 4,580,111 and 4,949,050 disclose an amplitude modulator for use in AM radio broadcasting and wherein the modulator serves to generate an amplitude modulated signal by selectively turning on and off a plurality of RF amplifiers in a digital manner to produce amplitude modulation. Each of the RF amplifiers provides an output voltage across the primary winding of a transformer. The secondary windings are connected together in a series circuit in a series combiner. Output current flows in the secondary windings to supply a load, such as an antenna for broadcasting an RF signal.
Frequently, such amplifiers are referred to as amplifier modules and such modules may be arranged side-by-side or stacked vertically. The modules are removably mounted in a cabinet so that each module may be removed for servicing or replacement. Before removal, the amplifier module is shut off but should not be removed until no current is flowing in the secondary windings. Normally, this requires that the transmitter be shut down. If such an amplifier module is turned off and an attempt is made to remove the amplifier from the series combiner, an open circuit will take place across the primary winding associated with the removed amplifier module. If the transmitter is still operating a high voltage potential will be developed across the open circuit of the primary winding and this will cause damage to the transformer and other associated circuitry. Consequently, the removal of such an amplifier module cannot take place while the transmitter is operating. The transmitter must be turned off before removing the amplifier module for repair. This creates discontinuity in the operation of the transmitter system.
SUMMARY OF THE INVENTION
In accordance with the present invention, apparatus and method are provided for use in disconnecting and/or replacing one of a plurality of M power amplifier modules in an RF transmitter while the transmitter is operating. Each amplifier module has first and second outputs that normally are connected across an associated one of M transformer primary windings. Also, M transformer secondary windings are provided with each associated with one of the primary windings. The secondary windings are connected together in series across a load. Each amplifier module has a control input for receiving a disable signal that disables the amplifier module. The apparatus for use in disconnecting and/or replacing includes a switch having a disable condition and an enable condition. A controller responds to the switch being in a disable condition for providing a disable signal. A shorting switch is provided having a normal open condition and a shorting condition and wherein the switch is connectable across the primary winding of an associated amplifier module to be disconnected and/or replaced. A shorting switch driver responds to the disable signal for driving the shorting switch to its shorting condition to short circuit the primary winding associated with the amplifier module that is to be disconnected and/or replaced.
REFERENCES:
patent: 4580111 (1986-04-01), Swanson
patent: 4780685 (1988-10-01), Ferguson
patent: 4949050 (1990-08-01), Swanson
patent: 5570062 (1996-10-01), Dent
patent: 5930128 (1999-07-01), Dent
Koontz David Roger
Luu Ky Thoai
Harris Corporation
Nguyen Patricia T.
Pascal Robert
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
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