I am an RF noob and am trying to understand if optimizing an AM crystal radio antenna (maximizing the signal transmission from the antenna to the LC tank) is practical, or even makes sense. Here is a schematic of the circuit I am working with:
My approach so far has been to treat my (theoretical) antenna (long wire) as a transmission line, and treating the LC tank as the load of the transmission line. In order to keep things simple, I have not considered loading by the diode. I reviewed a little literature about transmission line termination/impedance matching, and it seems that there would be some impedance value (implemented as a resistor between the antenna and the tank) which would maximize signal transmission at a given frequency.
Here are my questions:
- Does treating the antenna as a transmission line make sense?
- If so, how is the characteristic impedance of the antenna calculated?
- In adding a terminating resistor between the antenna and the tank, I would be making a voltage divider because I would 'read' the voltage between the tank and resistor i.e. this is where I would connect the diode. Would this potentially offset any gains I might make by impedance matching between the antenna and the tank?
- It seems that optimization may only be possible for one tank impedance, and, by extension, one specific wavelength. So, any 'optimized' design would only be able to listen to one radio station, and therefore not be useful even if it did work. Is that correct?