The tuned circuit consists of a variable capacitor and fixed air spaced coil. For the coil, I wound between 10 and 20 turns of wire on an empty tube of around 1.5 inches diameter. The turns were spaced so that the overall length was around 3 inches. The variable capacitor tuned 0 - 300 pF but there is plenty of scope for experiment here. One final point, you will need an external antenna to receive broadcasts. I have an outside wire that is about 7 meters long and this was quite effective.