HC-12 Range query

Hi guys,
I’m using a pair of HC-12s to send a string of data which is like 12 chars long.
I’m trying to achieve the max distance possible so ive got both devices in FU4 mode with a serial baud rate of 1200bps.
Im well aware that the 1000m or 1800m range will likely be from placing the device in line of sight and having the antennas above ground.
I am presently able to get about 120m range between both devices at the moment using an external 10cm 433mhz SMA antenna i bought off eBay. I tested this using line of sight with one of the devices on the ground and the other in my hand as i walked away from the device on the ground in an open rural space.
Has anyone got any advice or tips i can use to increase the range?
I am creating a remote which operates a relay over a distance and i would like to see 200m if possible.
The relay will be placed on a petrol buggy and is used to cut it off. The buggy will be expected to be moving about in an open field when in use.

The remote control (transmitter) device uses a Nano 5V and is connected to the HC-12 using software serial and i delay for 2000ms after each transmission since i am using FU4 mode. The remote control is powered by 2x 3.6V 18650 Li-Ion batteries connected to a OKI 78SR 5V/1.5A SMPS regulator. I dont have capacitors on the input or output of this as its battery powered. I’ve got a 22uF 50V capacitor across VCC and GND of both HC-12 devices.

The receiver device is powered by the 12V battery system of the buggy/ATV and uses the same regulator and HC-12 config. It also has the same 433mhz antenna and the capacitor.

I have simple test code I am using which send a character to the receiver and if correct will trigger a relay for a second, then after triggering the relay the receiver transmits back to the remote control and lights an LED for a second to let me know that the transmission was successful. I suppose i dont need the relay for the minute especially since I am only testing the code.
Ive included both the remote control and receiver code below to see if anyone can advise me on anything.

Hopefully someone will be able to give me some direction or maybe the ~120m is just the sort of limit i am likely to receiver.

Also if you guys know of any other UART or wire device I could use which could have better range than the HC-12, please do advise.

Thanks

See Code below.
Transmitter/remote control code

include <SoftwareSerial.h>
int LED = 3;
SoftwareSerial mySerial(8, 9); // RX, TX
void setup() {
  mySerial.begin(1200);
}
void loop() { // run over and over
   mySerial.print("A");
   delay(2000);
   
  if (mySerial.available()) {
   char A =mySerial.read();
 if(A=='B')
 {
  digitalWrite(LED,HIGH);
  delay(1000);
  digitalWrite(LED,LOW);
 }
  }
}

Receiver code

include <SoftwareSerial.h>

SoftwareSerial mySerial(8, 9); // RX, TX
int relay = 2;
void setup() {
  // Open serial communications and wait for port to open:
pinMode(relay,OUTPUT);

 digitalWrite(relay,HIGH);
  delay(1000);
  digitalWrite(relay,LOW);


  // set the data rate for the SoftwareSerial port
  mySerial.begin(1200);
 
}

void loop() { // run over and over
 while (mySerial.available()) {
   char A =mySerial.read();
 if(A=='A')
 {
  digitalWrite(relay,HIGH);
  delay(1000);
  digitalWrite(relay,LOW);
   mySerial.print("B");
   delay(2000);
 }
  }
}

The antennas are the problem.
Being only 10 cm long which is far less than 1/4 wave length which is 17 cm , it means that the antennas are a form of helical and can be inefficient depending on the exactly the frequency they are intended for.
Try a pair of 1/4 wave antennas which are simply a 17 cm length of wire soldered directly onto the HC12 board.

Indeed, dump the antennas, a lot of so called 'antennas' you can buy on eBay are junk.

Try plain 17cm wires.

Hi guys,
Thanks got the reply!!
Oh yes I never considered that the antenna would need to be 17cm as i did do the caluclation I will give it a go with the wire.
also as ive got the little ipx to SMA adapter and for robustness and tidyness do you think a pair of these Sander style FPV antennas would be any good? Link

Thanks guys
Really appreciate it
:smiley:

cfcorp:
Hi guys,
Thanks got the reply!!
Oh yes I never considered that the antenna would need to be 17cm as i did do the caluclation I will give it a go with the wire.
also as ive got the little ipx to SMA adapter and for robustness and tidyness do you think a pair of these Sander style FPV antennas would be any good? Link

Thanks guys
Really appreciate it
:smiley:

It will probably work, but its just a wire.

If you want a sticky up antenna just put a bit of wire in a plastic straw, or one of several types of thin plastic tube that are used for RC stuff.