You need to convert your udpMsg hex string to a byte array using something like so:
import javax.xml.bind.DatatypeConverter;
sendData = DatatypeConverter.parseHexBinary(udpMsg);
edit: try this method instead, I guess Android doesn't have the XML classes.
public static byte[] hexStringToByteArray(String s) {
int len = s.length();
byte[] data = new byte[len / 2];
for (int i = 0; i < len; i += 2) {
data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
+ Character.digit(s.charAt(i+1), 16));
}
return data;
}