I'm working on a sensor which purpose is to measure the water level of a sinkhole without getting in touch with the wastewater. The Sensor is mounted beneath the manhole cover --> The underside is formed like a rhomb and the sensor fits perfectly in the center bulge --> something like this --> similar Manhole Cover. The whole system is attached to the Manhole cover with strong magnets. The heart of the sensor is an ESP8266-12F. The whole system runs on 3,6 Volt.
An ESP8266-12F measures the distance between manhole cover and waterline via ultrasound (HC-SR04) uploads the measurement to Thingspeak if its able to locate a known WiFi nearby and additionally transmits the measurement via 433 MHz to a Receiving Unit. The receiving Unit uses and Arduino micro, a RTC modul and a 433 MHz receiving unit.
433 MHz transmitting and receiving unit are equipped with those antennas AntennaP Picture This are the 433 MHz Receiving and transmitting Units: 433 MHz Superheteodyn I want to achieve approximately 10 Meters transmitting distance from the manhole cover to the receiving unit.
I tested the system in my flat and on numerous distances without any problems and was really confident that an obstacle like the Manhole Cover + 10 Meters Air wouldn't be any problems. I knew that getting the signal out of the sink would be the tricky part because of all concrete and steel and I've got pretty much no experience with radio frequencies and the way they behave.
Today I was able to test the whole system --> The upload to ThingsPeak works like a charm. The WiFi has to be within 10 Meters from the manhole cover so that the ESP8266-12F is able to establish the connection. The 433MHz connection however fails. I need to be within 2 Meters of the manhole cover to get it to work.
Question: What could be the reason for this bad 433 MHz result. Why is the 2,4GHz Signal so much better than the 433 MHz signal ---> I thought when it comes to obstacles a lower frequency is better? Are the antennas bad? Can I improve them? Would it be better to use a long Cable with 17 cm? (Lambda/4) Would it work better with higher VCC than 3,6 V. As far as I know the transmitting unit isn't supposed to go over 3,8 V. The receiving unit runs on 5 Volt from the arduino micro?