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Simple QRSS transmitter

Discussion in 'Homebrew and Kit Projects' started by SA7CNG, May 10, 2018.

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  1. SA7CNG

    SA7CNG Ham Member QRZ Page

    I have just started to put together a QRSS beacon transmitter, from some parts i had in my workshop. The transmitter is supposed to fit nicely into a junction box, for mounting outdoors.

    The size wasnt an issue as i thirst thought, i solderd together a colpits oscillator with a simple class A amplifier circuit, and with 13V it outputs about 50-60mW of RF into a 50ohm dummy load. Current draw is about 50mA, about 600mW, so effiency isnt that good, just about 10%. At the moment the circuit is equippped with a 7030kHz crystal, i will try to find a 30m one.

    Power supply will come from a battery, probalby solar charged. The circuit will be controlled by a AVR microprocessor, ATTINY25 or something like that.

    Does anyone know if 50mW is OK for QRSS? Or should i put a PA on the board and get 500mW instead? And what kind of speed would be good to start with? QRSS10?

    [​IMG]

    [​IMG]
     
    VK4FFAB likes this.
  2. VK4FFAB

    VK4FFAB Subscriber QRZ Page

    Looks good, great project.
     
  3. SA7CNG

    SA7CNG Ham Member QRZ Page

    I have added the microprocessor and its help circuitry(3,3v regulator, 10k reset pull upp etc..). The Attiny has one input and one output, the output is keying the transmitter with a BC547 transistor that grounds the amplifier emitter. And the input messures the voltage through a 1/10 voltage divider with a ADC.

    In this configuration the oscillator will always be running, even when the circuit is not running. The RF-power should be very low, perhaps below a mW, so it should be OK.

    The ADC battery voltage messurement is so that the circuit doesnt drain the battery completely, the stop voltage needs to be set for what sort of battery thats beeing used, and i havent really decided on what sort of battery to use. Perhaps the circuit should be powered by a solar panel only?

    [​IMG]
     
  4. KD4MOJ

    KD4MOJ Platinum Subscriber Platinum Subscriber QRZ Page

    [​IMG]

    [​IMG]

    Plenty... you can join the folks on 22 meters (13.560) [LINK] running QRSS for low power experimentation. If I remember correctly, you can run up to 10mw legally.



    ...DOUG
    KD4MOJ
     
  5. SA7CNG

    SA7CNG Ham Member QRZ Page

    A first version of the code is now complete, and tested. It transmitts QRSS10, if battery voltage is above 8.5V. I also added a diode to the board for debugging.

    The only thing i havent been able to check is the RF-output, will try to find a oscilloscope to check that everything is OK there.

    With a 47ohm dummyload the circuit draws about 70mA, not too bad, although 10mA is for the led that can be removed.

    Now i just need a 10140kHz crystal, seams a bit difficult to find...

    [​IMG]

    Code:
    #define F_CPU 1000000 //Define clock speed
    #include <avr/io.h>
    #include <util/delay.h> //Needed for delay function
    
    
    int speed = 100;
    
    void delay_ms(uint16_t n) {
        while (n--) {
            _delay_ms(1);
        }
    }
    
    int main(void)
    {
        DDRB |= (1 << 0);    //Set PB0 till output, 1 = output, 0 = input
      
        ADMUX =        //Konfiguera ADC, referens och kanal.
        (1 << ADLAR) |
        (0 << REFS1) |
        (0 << REFS0) |
        (0 << MUX3)  |
        (0 << MUX2)  |
        (1 << MUX1)  |
        (1 << MUX0);
    
        ADCSRA =        //Configure ADC
        (1 << ADEN)  |
        (1 << ADPS2) |
        (1 << ADPS1) |
        (0 << ADPS0);
    
        while(1)
        {
            ADCSRA |= (1 << ADSC);         // start ADC measurement
            while (ADCSRA & (1 << ADSC) ); // wait till conversion complete
            speed = 10000;                    // set dot length to 10s
            if(ADCH > 50)                    //Compare voltage, set limit at 8.5V
                    Sendcq();
        }
    }
    
    
    void Dash(void)
    {
        PORTB |= 1 << PB0;
        delay_ms(3*speed);
        PORTB &= ~(1 << PB0);
        delay_ms(speed);
    }
    void Dot(void)
    {
        PORTB |= 1 << PB0;
        delay_ms(speed);
        PORTB &= ~(1 << PB0);
        delay_ms(speed);
    
    }
    
    void Sendcq(void)
    {
        Dash();
        Dot();
        Dash();
        Dot();
        delay_ms(3*speed);
        Dash();
        Dash();
        Dot();
        Dash();
        delay_ms(7*speed);
          
        Dash();
        Dot();
        Dot();
        delay_ms(3*speed);
        Dot();
        delay_ms(7*speed);
      
        Dot();
        Dot();
        Dot();
        delay_ms(3*speed);
        Dot();
        Dash();
        delay_ms(3*speed);
        Dash();
        Dash();
        Dot();
        Dot();
        Dot();
        delay_ms(3*speed);
        Dash();
        Dot();
        Dash();
        Dot();
        delay_ms(3*speed);
        Dash();
        Dot();
        delay_ms(3*speed);
        Dash();
        Dash();
        Dot();
        delay_ms(7*speed);
      
    }

     
  6. K6CLS

    K6CLS Ham Member QRZ Page

    That's right in the PSK and JT area. Maybe 10116 would be better, people expect to find QRP there?
     
  7. SA7CNG

    SA7CNG Ham Member QRZ Page

    I think 10.140kHz is the best place to be, as i understand it all the QRSS grabbers are located there. The lack of 10140kHz crystals is a problem though, is there any way to offset a collpits crystal oscillator from the crystal frequency?
     
  8. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Add a variable capacitor....
     
  9. SA7CNG

    SA7CNG Ham Member QRZ Page

    I did an experiment and connected a 100pf and then a 2200pf capacitor between the crystal and ground, but it didnt move the oscillation frequency more than a kHz or something like that(my FT817 doesnt have very narrow filters, and i need an oscilloscope to messure the frequency...)
     
  10. VK3YE

    VK3YE Ham Member QRZ Page

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