Finding a septic tank via radio-direction finding
A friend of mine did not know where the septic tank in their home was. I’ve figured out that this could be a fun opportunity for radio direction finding. A while back I bought several super cheap 433MHz OOK transmitters. They are about $1-$2 each -- not too much for literally throwing something down the drain.
I soldered a small LiPo battery, connecting both VCC and data to the 3.3V+ of the batter, having the device on transmit mode all the time. I also soldered a 10cm wire to the antenna port.
To keep everything waterproof, I put the setup in a small bag -- and sent it down the toilette with the help of my assistant Alan!
It took a few tries, but the package was drained and started flowing towards the tank. For tracking I used my new IC-705, which has a nice waterfall plot on the screen, so I can see the peak. For antenna, I used the Arrow.
It was nice seeing how the frequency of the transmitter changes as it is loaded by the water-- but then stabilizing nicely once it set still (consecutive toilette flushing would shift the frequency a little bit!). Using this setup we were able to identify the location of the tank, which ended up underneath the deck!
