RF Modem 433MHz Receiving Noise

Hi all,

I recently bought a few pairs of these:

Before I even connected the Transmitter, I wired up the receiver. When I connect the receiver module to my Arduino, I get a bunch of random garbage. I connect the data line to my oscilloscope, and there is a bunch of random data on the line, sometimes not even anything that looks like real data.

Oddly enough, when I touch my finger on the corner of the receiver board, the noise goes away and the data line sits nicely at 5V. I touch the surface mount components right above the coil that sits in the lower corner of the board.

I have tried 2 different receivers and see the same activity.

Anyone have any ideas?

#include <SoftwareSerial.h>

//Compiler Macros
const char compile_date[] = __DATE__ ;
const char compile_time[] = __TIME__;
const char filename[] = __FILE__;

SoftwareSerial mySerial(2, 3); // RX, TX

const int pinLED = 7;

byte a[10];

int numBytes = 0;
int i = 0;
unsigned long t1,t2,t3;
//////////////////////////////////////////////////////////////////////////////////

void setup()
{
  pinMode(pinLED,OUTPUT);
  digitalWrite(pinLED,HIGH);
  Serial.begin(9600);
  mySerial.begin(4800);
  setupStream();
  t1 = millis();
  t2 = t1;
  t3 = t1;  
}
/////////////////////////////////////////////////////////////////////////////////////////
void loop()
{
 t1 = millis();
 if((t1-t2) > 10000)
 {
   t2 = t1;
 }
  numBytes = 0;
  if(mySerial.available()>0)
  {
    delay(50);
    
    numBytes = mySerial.available();
 
    for(i=0;i<numBytes;i++)
    {
      a[i] = mySerial.read();
      delay(5);
      digitalWrite(pinLED,LOW);
      delay(100);
      digitalWrite(pinLED,HIGH);
    }

    Serial.print("Message received at: ");
    Serial.println(t1/1000);
    for(i=0;i<numBytes;i++)
    {
      Serial.print(i);
      Serial.print(": ");
      Serial.println(a[i]);
    }
    Serial.println();
    Serial.println();
  }


}

Working fine , all those cheapo receivers do that as they cant tell the differance between a wanted signal and thermal noise.
You have also bought the worst type possible which are superregens and are by design unstable which is why putting your finger on the board is causing the effects you are seeing.

Hi Mauried,

Thing is, when I do not touch anything, the signal is biased towards GND but very noisy. As soon as I touch the board, it goes to 5V, and the signal is clean.

Next time I'll but the Rx/Tx set from Sparkfun - I've gotten those to work without any problems in the past.

The signal isnt clean , the receiver is just not working if you put your finger anywhere near the coil as the quench oscillator stops and then the receiver stops.
Depending on your application either buy the receivers which are superhets and they have a crystal on the pcb , or go for much better radios like HC12s.

Hi Mauried,

Thanks for the advice - it has been a while since I've done any RF work.

I'll probably go for the HC12 or something similar.

If you want to save a dollar or 2 , there is a HC11 which is basically a HC12 with a lower output power, but uses a differant radio chip, so HC12s arnt compatible with HC11s.
The serial interface is the same though.