JPH0456522A - Transmission output variable system - Google Patents

Abstract

PURPOSE:To vary an output without degradation in the characteristic of a transmitter by controlling a high frequency switch so as to decrease the number of power amplifiers for which an exciting signal is applied when a reflection power from a load of a transmitter reaches a specified value or above. CONSTITUTION:The system is provided with an excitor 1 outputting an exciting signal, a changeover switch 2 having high frequency switches 21-2n, power amplifiers 11-1n, a directional coupler 3 to detect a reflected power component from a transmission antenna 5, and a control circuit 4 controlling the changeover switch 2 in response to the reflected power. When VSWR of an output of the transmitter is degraded and the reflected power is increased to be a prescribed value or above, the control circuit 4 activates the prescribed number of the high frequency switches among the frequency switches 21-2n to select the exciting signal to be switched to a termination resistor R, thereby reducing the transmission power. Since the operating state of the power amplifier is almost unchanged, the change in the characteristic is prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a variable transmission output system for a transmitter that combines the outputs of a plurality of power amplifiers to obtain transmission power. The present invention relates to a variable output system for a TV transmitter that does not cause

[Conventional technology]

A transmitter that is currently broadcasting cannot be allowed to stop transmitting radio waves due to interference, no matter what the environment.

For example, when ice builds up on the transmitting antenna, the VSWR of the load on the transmitter deteriorates and the reflected power increases, causing a failure when it exceeds a specified withstand voltage value. In order to prevent such failures, a variable transmission output system is provided that detects reflected power on the output side of the transmitter and reduces the transmission power of the transmitter when the reflected power exceeds a specified value.

FIG. 2 is a diagram showing an example of a conventional transmission output variable system, in which an exciter 1 outputs an excitation signal, a variable attenuator 6 adjusts the level of the excitation signal, power amplifiers 11 to 1n, and a transmission output output from the transmission antenna 5. A directional coupler 3 for detecting reflected power components and a control circuit 7 for controlling a variable attenuator 6 according to the reflected power value are provided. Now, when the control circuit 7 detects that the reflected power value has exceeded the specified value, it controls the attenuation amount of the variable attenuator 6 to increase, and the power amplifiers 11 to
By reducing the level of the excitation signal supplied to 1n, the output power of the power amplifiers 11 to 1n is reduced, and as a result, the transmission power of the transmitter is reduced.

[Problem to be solved by the invention]

Generally, in the case of a TV transmitter, in order to compensate for the nonlinearity that occurs in the power amplifier, a linearity compensation circuit (not shown) having characteristics opposite to those of the power amplifier is provided in the exciter, and the transmitter The linearity compensation circuit is adjusted so that overall linearity is good when operating at the output. In the conventional transmitter output variable system described above, when the reflected power value exceeds a specified value, the level of the excitation signal supplied to the plurality of power amplifiers is uniformly reduced.
Each power amplifier operates outside of its normal output operating state. Therefore, there is a problem that not only the characteristics of the linearity compensation circuit and the characteristics of the power amplifier do not match, but also that the characteristics of each power amplifier are different, so that the overall characteristics are deteriorated.

An object of the present invention is to provide a variable transmission output system that does not cause characteristic deterioration even when the output of a TV transmitter is changed.

[Means to solve the problem]

The transmitter output variable system of the present invention is a transmitter output variable system in which one excitation signal is supplied to a plurality of power amplifiers and the respective outputs are combined to obtain transmission power. reflected power detection means for detecting a reflected power value by detecting a reflected power value; switching means for turning on and off the excitation signal input to each of the plurality of power amplifiers according to a control signal; and a control means for generating and outputting the control signal. The switching means may include a plurality of high-frequency switches each connected to an input side of the plurality of power amplifiers and transmitting the excitation signal to either one of the terminating resistor and the power amplifier according to the control signal. You can.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, in which an exciter 1 outputting an excitation signal, a switching device 2 having high frequency switches 21 to 2n, and power amplifiers 11 to 1
n, a directional coupler 3 for detecting the reflected power component from the transmitting antenna 5, and a control circuit 4 for controlling the switch 2 according to the reflected power value. High frequency switch 21-2
n is connected to the input side of each of the power amplifiers 11 to 1n, and switches the excitation signal to the power amplifier side or to the termination resistor R side according to a control signal from the control circuit 4.

Now, the specified transmission power of the transmitter is Po, and the load of the transmitter is V.
When SWR is γ, reflected power W0 is expressed by equation (1).

Wo = ((r −1) / (r+ 1))2−
Po-(1) Now, the VSWRγ on the output side of the transmitter has deteriorated and the reflected power W has increased. Suppose that increases and exceeds the specified value,
The control circuit 4 includes n high-frequency switches 21 to 2n,
The m high-frequency switches are activated to switch the excitation signal to the terminating resistor side. Therefore, the excitation signal from exciter 1 is (
Since the transmission power P1 is supplied only to (n-rn) power amplifiers, the transmission power P1 at this time is expressed by equation (2).

P 1=Po ・((n m) / n)” −(
2) Also, the reflected power W1 at this time is (1), (
2) Formula % Formula % It can be reduced.

When the transmission power is reduced in this way, (n-m
) power amplifiers do not change in any way, so
Changes in characteristics can be prevented.

〔Effect of the invention〕

As explained above, according to the present invention, high frequency switches that turn on and off excitation signals are connected to the input sides of a plurality of power amplifiers, respectively, and when the reflected power from the load of the transmitter exceeds a specified value, Since the transmitter output is reduced by controlling the high frequency switch and reducing the number of power amplifiers that apply excitation signals, the operating state of the power amplifiers does not change, and therefore the output can be reduced without deteriorating the transmitter characteristics. Can be changed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing an example of a conventional transmitter output variable system. DESCRIPTION OF SYMBOLS 1... Exciter, 2... Switcher, 3... Unidirectional coupler, 4... Control circuit, 5... Transmission antenna, 6...
- Variable attenuator, 7... Control circuit, 11-1n... Power amplifier, 21-2n... High frequency switch.

Claims (1)

[Claims] 1. In a variable transmission output system of a transmitter in which one excitation signal is supplied to a plurality of power amplifiers and the respective outputs are combined to obtain transmission power, the power reflected from the load of the transmitter is detected. reflected power detection means for detecting a reflected power value; switching means for turning on and off the excitation signal input to each of the plurality of power amplifiers according to a control signal; 1. A variable transmission output system comprising: control means for generating and outputting a control signal. 2. The switching means includes a plurality of high-frequency switches each connected to an input side of the plurality of power amplifiers and transmitting the excitation signal to either one of the terminating resistor and the power amplifier according to the control signal. The variable transmission output system according to claim 1, characterized in that: