Important: Any RF research shall observe local regulations first, some of which are very strict. This blog shall be used for research purpose only in well-functional EMC safe environment without RF leakage or interference to Other frequency-Bands.

Simplicity RF Transmitter

1. Introduction

Simplicity Homebrew RF Transmitter is based on innovative Wideband RF Power LDMOS Transistor MRF101AN with operation frequency up to 230MHz.

Limited by the frequency of transistors, the high frequency RF transmitter normally requires LC oscillator. In this design of simplicity RF transmitter, waveform generated by high performance MCU shall be transmitted directly without filters or modulators. This task challenges the performance of MOS transistor but reduce the complexity of RD designs.

In this design, MRF300AN type 100 W CW over 1.8-250 MHz, 50 V Wideband RF Power LDMOS Transistor and Arm-M33 core 100MHz LPC55S6x MCU shall be used for best parameter-matching.

2. Scheme

2.1 Program flow

This MCU produce square waveform with PWM on GPIO port, the output voltage shall be 10mA in 3.3V , just enough drive the MRF101AN directly, relieving the the work of MOSFET driver selection.

Then, the MRF101AN drive high frequency antenna to transmit the RF power to nearby area. The antenna shall be carefully configured to match the function. The transmission power shall be decided by the driven voltage applied on source pin ranging 3.3V to 50V.

2.2 Scheme of the Design

 

According to the datasheet of LPC55S69, the master time shall be ported through the PWM pins with maximum of 100MHz. Two PWM pin in opposite phase, mean the Q1 and Q2 shall be in reverse phase to send the power delivery up to antenna.

The antenna shall be single pole , the balun and transmission line shall be design accordingly.

It is clear that the design need test and adjust for better performance and local RF management codes and rules shall be carefully observed. In experimental phase, the Vcc can not be set high to make minimum RF dB according to EMC regulations.

 

3. BOM

IDNameDesignatorFootprintQuantityManufacturer Part
1CONNECTORPMWDIP-2X2.54MM-4P1DS1023-2*2SF11
2NXP MRF300ANQ2,Q1TO-247-32NXP
347pFC1,C2,C3RAD-0.13
4Balun Customized50ohm1Customized
5AntennaCustomized50ohm1Customized
6Transmission LineCustomized50ohm1Customized
7LPC55S69-HLQFP1001NXP
8Accessaries--1-

4. Design

4.1 Antenna Part

Single pole antenna shall be used with flat copper plate size of at least , in the center one length-adjustable pole with .

As of , .

4.2 MCU part

LPC55S69-EVK Development board shall be used in this demo project with PWM frequency up to 100MHz.

Here is the demo code as regular square wave form in 100Mhz same as the master clock.

Since this is new development board, I have not put it into operation until this submission deadline. Therefore, I use NXP RISC core RV31 development board in eclipse C++ for RISC.

Here is part of the code.

#include "board.h"
#include "fsl_debug_console.h"
#include "fsl_gpio.h"


#include "clock_config.h"
#include "pin_mux.h"


#define BOARD_A0_GPIO PORTC
#define BOARD_A0_GPIO_PIN 11U
#define BOARD_A1_GPIO PORTC
#define BOARD_A1_GPIO_PIN 12U
/*******************************************************************************
 * Prototypes
 ******************************************************************************/
/*!
 * @brief delay a while.
 */
void delay(void);


/*******************************************************************************
 * Variables
 ******************************************************************************/


/*******************************************************************************
 * Code
 ******************************************************************************/
void delay(void)
{
    volatile uint32_t i = 0;
    volatile uint32_t n = 1;
    for (i = 0; i < 5000000; ++i)
    {
        __asm("NOP"); /* delay */
    }
}


/*!
 * @brief Main function
 */
int main(void)
{
    /* Define the init structure for the output A0&A1 pin*/
    gpio_pin_config_t A0_config = {
        kGPIO_DigitalOutput, 0,
    };
    gpio_pin_config_t A1_config = {
        kGPIO_DigitalOutput, 1,
    };


    /* Board pin, clock, debug console init */
    BOARD_InitPins();
    BOARD_BootClockRUN();
    BOARD_InitDebugConsole();


    /* Print a note to terminal. */
    PRINTF("\r\n Simple RF transimitter\r\n");
    PRINTF("\r\n The A0&A1 is osilating.\r\n");


    /* Init output LED GPIO. */
    GPIO_PinInit(BOARD_A0_GPIO, BOARD_A0_GPIO_PIN, &A0_config);
    GPIO_PinInit(BOARD_A1_GPIO, BOARD_A1_GPIO_PIN, &A1_config);


    while (1)
    {
        delay();
        GPIO_TogglePinsOutput(BOARD_A0_GPIO, 1u << BOARD_A0_GPIO_PIN);
        GPIO_TogglePinsOutput(BOARD_A1_GPIO, 1u << BOARD_A1_GPIO_PIN);
    }
}

4.3 Test Build in Breadboard

Wiring the components as scheme above,

5. Performance and Next Steps

After the build of whole design, after voltage of 5.0V is applied onpin, there is no obvious signal detected. More research shall be done on this design in the following scope.

The characteristic impedance of transmission line, antenna and balun shall be recalculated and adjusted. Since unwanted bump-back of RF wave shall increase the heat loss instead of RF power dispatching.

Another part is power efficiency optimizing, different voltage shall be applied on pin to test the performance of MRF300AN.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

- First blog posted on 2019-10-9 15:19:37 as, then revised and updated.

 

1. There have long history of RF harnest . The small amount of power can drive high impedance load like earphones. But not enough for IC chips.

2. The TI BQ25570 is good for such purpose can harnest small amount of irregular  power source as low as 100mV.

3. Therefore it is good if it can meet such need.

4. In recent calculation, one double pole attena with square wave up to 100MHz can deliver power to direction for one squar frame attena to catch the wave as power source for BQ25570.

5. There are too many math calculation for transmission line match, attena design. All the calculation process shall be detailed here for verification.

Coming soon with math formulars and boresome results.