the invention is for use as part of a system that typically includes wireless equipment 20 such as a radio modem for transmitting and receiving communication , a power injector 30 , an amplifier 40 , an antenna 28 , and cabling 22 , 24 , 26 connecting each of these components together as illustrated , for example , in fig1 . the system may be in a wireless local area network ( wlan ), or wireless local loop ( wll ). the system may be applied to wireless internet access ( wia ) point - to - point and point - to - multipoint applications . this invention allows the user of the wireless equipment 20 to set the level of output power given to a transmission signal by setting the level preferably through the power injector 30 that sets a voltage for the transmission on the cable that is detected by the amplifier 40 that then adjusts the output power of the transmission based on the set voltage . the amplifier 40 preferably is a bi - directional amplifier . [ 0030 ] fig1 illustrates the system having a module ( or amplifier ) 40 in accordance with a first preferred embodiment of the present invention . a radio modem 20 is connected to send signals to and receive signals from an rf cable 22 . the radio modem 20 includes circuitry to implement a time division duplex ( tdd ) protocol , and to otherwise meet the user &# 39 ; s needs . a power injector 30 passes signals between the cable 22 and a cable 24 , and superimposes a dc voltage on the rf signal on the cable 24 . the level of the dc voltage is variable by manual manipulation of a control knob 32 . the power injector 30 is typically located in a protected environment , such as a shelter or inside the building , and proximate to radio modem 20 or other wireless rf equipment . the cable 24 communicates signals between the power injector 30 and the module 40 . the module 40 amplifies rf signals received from the cable 24 , and sends the amplified signal to an antenna 28 . the module 40 is powered by the dc voltage on the cable 24 . the module 40 is mounted on the pole of antenna 28 on the exterior of a building . the module 40 may be mounted on the pole using any number of means including u - bolts , clamps , etc . preferably , the housing for the module 40 is small and waterproof , to provide for direct mounting on the antenna 28 . the illustrated embodiment includes a housing having n - type , male , 50 ohm connectors adapted for quick connection to standard commercially available n - type , female , 50 ohm connectors disposed on the connecting cables . [ 0035 ] fig2 illustrates the power injector 30 in more detail . a voltage regulator 34 generates four voltages : v 1 , v 2 , v 3 , and v 4 . in this example , v 1 equals 9 volts , v 2 equals 10 volts , v 3 equals 11 volts , and v 4 equals 12 volts . a control knob 32 includes a 4 - to - 1 switch for connecting ( or applying ) a selected one of voltages v 1 , v 2 , v 3 , or v 4 to the lower terminal of the inductor 36 . the voltage regulator 34 and control knob 32 may be designed to provide two or more output power levels . a capacitor 38 blocks a dc current from passing between the voltage regulator 34 and the cable 22 . an inductor 36 blocks the rf signal from passing to the regulator 34 from either cable 22 and / or 24 . [ 0037 ] fig3 shows certain circuitry in the module 40 . at the time depicted in fig3 the module 40 is in the transmit mode , meaning that a switch 422 transfers a signal on the cable 24 through the transmission amplifier module ( or transmission pathway ) 44 to the antenna 28 via switch 424 . an exemplary embodiment of the transmission amplifier 44 includes a driver amplifier 442 and a power amplifier 446 as illustrated in fig3 . an input of digital attenuator 444 receives the output of the driver amplifier 442 . the digital attenuator 444 attenuates the received signal from the driver amplifier 442 as dictated by a control input ( or signal ) from a dc level sensor ( or detector ) 448 , and transfers the attenuated signal to the input of the power amplifier 446 . the power amplifier 446 transfers an output signal to the antenna 28 via the switch 424 . in the receive mode , the switches 422 and 424 are in the opposite position of that depicted in fig3 . an exemplary receive path is illustrated in fig3 and described herein is a receiving amplifier module ( or path or means ) 46 . a low noise amplifier ( lna ) 462 receives a signal from the antenna 28 , via the switch 424 , and transfers an amplified signal to the input of a band pass filter 464 . the band pass filter 464 transfers a filtered output to the input of a low noise amplifier 466 . the low noise amplifier 466 transfers an amplified signal to the input of a band pass filter 468 . the band pass filter 468 transfers the filter output to the cable 24 via the switch 422 . as one of ordinary skill in the art will appreciate based on this disclosure , a variety of receive circuitry found in bi - directional amplifiers could be used for the receive path 46 in the illustrated bi - directional amplifier . in other words , the module 40 toggles between a transmitting mode and a receiving mode . in the transmitting mode , the switch 424 operatively connects the amplifier 446 to the antenna 28 . in the receiving mode , the switch 424 directs an antenna signal to the receive path 46 . [ 0040 ] fig4 emphasizes certain circuitry in the dc level sensor 448 . the respective + input of each of comparators ( means for determining the voltage level of the signal being transmitted ) 4482 , 4484 , 4486 receives a signal from the cable 24 . the − input of the comparator 4482 receives a reference voltage substantially equal to ( v 1 + v 2 ) 2 , causing the comparator 4482 to apply a digital output u 1 to a 3 : 4 decoder 4488 ( means for coding a signal to instruct the attenuator 444 the level of attenuation to apply to the signal being transmitted ). v 1 and v 2 are two of the user selectable voltages sent from the power injector 30 , as illustrated in fig2 . the − input of the comparator 4484 receives a reference voltage substantially equal to ( v 2 + v 3 ) 2 , causing the comparator 4484 to apply a digital output u 2 to the 3 : 4 decoder 4488 . v 3 is one of the user selectable voltages sent from the power injector 30 , as illustrated in fig2 . the − input of the comparator 4486 receives a reference voltage substantially equal to ( v 3 + v 4 ) 2 , causing the comparator 4484 to apply a digital output u 3 to the 3 : 4 decoder 4488 . v 4 is one of the user selectable voltages sent from the power injector 30 , as illustrated in fig2 . table 1 below shows functionality of the 3 : 4 decoder 4488 . the decoder 4488 produces output ( y 1 , y 2 , y 3 , and y 4 ) as a function of input ( u 1 , u 2 , and u 3 ). table 1 also shows the functionality of the comparators 4482 , 4484 , 4486 . the comparators 4482 , 4484 , 4486 produce outputs ( u 1 , u 2 , and u 3 ) as a function of a dc voltage on the cable 24 . one of ordinary skill in the art will appreciate that if a number other than four output power levels are provided for at the power injector 12 , that the number of comparators can be scaled up or down to correspond to the number of possible output power levels . [ 0047 ] fig5 illustrates an implementation of the 3 : 4 decoder 4488 using digital logic components that are capable of providing the outputs shown in table 1 for the inputs representative of the desired output power level . [ 0048 ] fig6 shows additional circuitry preferably connected to an input node 402 in module 40 . a dc / dc converter 482 generates a 12 volt reference , used to generate the references applied to the − inputs of the comparators of fig4 . a voltage regulator 484 produces 7 volts for powering the power amplifier 446 . in other words , although the dc voltage on node 402 may vary between 9 and 12 volts , the voltage regulator 484 applies a constant voltage of 7 volts to the power amplifier 446 . [ 0049 ] fig7 shows exemplary circuitry for the module 40 to control the switching of switches 422 , 424 , including an rf power sensor 486 and a switching controller 50 having a voltage comparator 502 connected to the output of the power sensor 486 . the voltage comparator 502 provides an output to a switch controller 504 that generates a signal “ t / r switch .” the signal “ t / r switch ” controls whether the switches 422 and 424 are in the transmit position or the receive position . an element 506 provides a transmission voltage threshold to comparator 502 . the module 40 thereby switches from transmit to receive mode automatically when the rf power is below the threshold level provided by element 506 . the voltage comparator 502 , the element 506 , and the switch control 504 together can be considered to be a switching controller 50 . the first preferred embodiment of the invention preferably incorporates protective features such as lighting protection circuitry and power surge protective circuitry to prevent damage from operational or environmental anomalies . thus , the first preferred embodiment of the invention provides a standardized amplifier that is economical to install , and usable with a broad range of hardware and in a broad range of operational environments . [ 0052 ] fig8 is a diagram illustrating another exemplary embodiment of the system in accordance with the present invention . the illustrated system includes a variable gain amplifier 441 at the input of amplifier 442 in the transmission amplifier 44 . amplifier 441 , rf power sensor 486 ′, and gain control circuit 440 cooperate to provide a substantially constant input to the amplifier 442 . [ 0053 ] fig9 illustrates a possible implementation of rf power sensor 486 ′. as one of ordinary skill in the art will appreciate , the implementation illustrated in fig9 may be used for the rf power sensor 486 by eliminating the connection to the gain control 440 . [ 0054 ] fig1 illustrates a possible implementation of gain control circuit 440 , which receives the output of power sensor 486 ′. gain control circuit 440 essentially subtracts the output of rf power sensor 486 ′ from a reference voltage , and applies the subtraction result to a control input of variable gain amplifier 441 . thus , the amplifier 441 remains at a predetermined output power level independent of the rf input power level on input node 402 . alternatively , amplifier 442 may be omitted from this exemplary embodiment . [ 0055 ] fig1 illustrates a possible implementation of the variable gain amplifier 441 . a variable attenuator at - 110 has a control input that receives the output of the gain control circuit 440 illustrated in fig1 . [ 0056 ] fig1 illustrates a possible implementation of switching control circuit 50 ′. as one of ordinary skill in the art will appreciate , the implementation illustrated in fig1 may be used for switching control circuit 50 . a voltage comparator has a − input connected to the output from the power sensor 486 ′. the voltage comparator has a + input connected to a 10k : 300 resister divider that provides a threshold to distinguish between transmitting and receiving . the circuit 50 ′ provides a two line output to transmit / receive switches 422 and 428 to switch between the transmit and receive modes depending on the output voltage . the two line output includes the signals rx - v and tx - v shown in fig1 . this embodiment thereby switches from transmit to receive mode automatically when rf power is below the threshold level . alternatively , a single or pair of led ( s ) may be included to indicate in which mode the module is operating in . circuits to implement rf power sensor 486 ′, gain control circuit 440 , and variable gain amplifier 441 are described in u . s . application ser . no . 09 / 524 , 745 , of david ge , filed mar . 14 , 2000 for smart amplifier for time division duplex wireless applications , the contents of which are hereby incorporated by reference . these circuits collectively are means for normalizing the signal input into said attenuating means based on the voltage of the transmit signal . numerous other embodiments are possible . for example , although a control knob has been illustrated and discussed for the dc level control knob 32 for the power injector 30 , there are numerous other ways of effecting power control . for example , power control may be adjusted with dedicated buttons or slides on or connected to the power injector 30 , or may be adjusted in response to commands originating from a conventional keyboard connected to a general purpose computer . these various ways for effecting power control are covered by mechanical actuator . different exemplary embodiments have been described above with various components that can be grouped into functional groupings . means for switching between receive and transmit modes includes rf power sensor 486 , switching controller 50 , 50 ′, and switches 422 , 424 . means for setting the output power level of a transmission signal based on the voltage of the transmit signal and providing a control signal includes the dc level sensor 448 . means for attenuating the transmit signal based in part on the control signal includes the attenuator 444 , and under at least one embodiment the transmission amplifier 44 . means for amplification of a received signal includes the receiving amplifier path 46 and its illustrated embodiments . means for setting a desired output level for the transmission signal include actuator 32 and voltage regulator 34 . benefits , other advantages , and solutions to problems have been described above with regard to specific examples . the benefits , advantages , solutions to problems , and any element ( s ) that may cause any benefit , advantage , or solution to occur or become more pronounced are not critical , required , or essential feature or element of any of the claims . additional advantages and modifications will readily occur to those skilled in the art . the preferred embodiment of the invention in its broader aspects is therefore not limited to the specific details , representative apparatus , and illustrative examples shown and described . accordingly , departures may be made from such details without departing from the spirit or the scope of applicants ′ general inventive concept . the preferred embodiment of the invention is defined in the following claims . in general , the words “ first ,” “ second ,” etc ., employed in the claims do not necessarily denote an order . as used herein “ substantially ” is a relative modifier intended to indicate permissible variation from the characteristic so modified . it is not intended to be limited to the absolute value or characteristic which it modifies but rather approaching or approximating such a physical or functional characteristic . given the foregoing , it should be apparent that the specific described embodiments are illustrative and not intended to be limiting . furthermore , variations and modifications to the preferred embodiment of the invention should now be apparent to a person having ordinary skill in the art . these variations and modifications are intended to fall within the scope and spirit of the preferred embodiment of the invention as defined by the following claims .