433Mhz RF transmitter antenna

I used a 30cm wire for my 433Mhz transmitter. I used the transmitter (along with HT12E) for my project. It works fine with wire antenna itself.

hi,
I'm having trouble with the transmission. I used following codes for transmission and reception in avr microcontrollers to blink an LED. Sometimes it works very well (LED blinks) when the relevant button is pressed and sometimes it doesn't. I am using 173mm antennas. Any suggestions guys?
TX

if (ButtonPressed(0, PINC, 0, 70))	{			while (! (UCSRA & (1 << UDRE)) );		UDR = 0x55;				while (! (UCSRA & (1 << UDRE)) );		UDR = 0b10111001;	}

ISR(USART_RXC_vect) 
{	receiveData = UDR;if(receiveData==0b10111001){	PORTB|= (1<<PINB0);	_delay_ms(100);	PORTB^= (1<<PINB0);}

}