Radio Links, Notes, and Resources

Crystal Radio

Coil Calculation:
Dave's Homemade Radios:
I've found that only two coil inductance sizes are used for most radios. The nominal values are 240 and 150µH. The 150µH coil is used as a T-Tuner (Tuggle Tuner). This is a simple hookup usually using a dual 365pF type variable capacitor and the 150µH coil. The coil is connected from the rotor to a stator. This stator is also the radio ground connection. The other stator goes to your antenna. This provides overall good coupling, while maintaining a reasonable circuit Q across the entire band. This circuit is used in all my two coil dx crystal receivers.
The 240µH coil is used in the detector tuned circuit. The detector coil is inductively coupled to the antenna coil mentioned above. This coil will resonate the entire MW band without changing coil taps or adding an extra capacitor and the switch. The capacitor should be a 365-15pF type.

1929 Style

VE7SL Radio Notebook: