Quote:
Originally Posted by Neil Purling
The lowest frequency of the Long Wave band is around four times lower than the low frequency end of Medium Wave. For Medium wave I had 65 turns, tapped at 5 turns. In winding a coil four times larger I tapped it at 20 turns.
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You may have to make some slight corrections to your new coil data.
A (very) rough formula for the inductance of an airwound coil is
I (uH) = D * N^2 / ( 100* (0.43 + L/D ))
Where D and L are the Diameter and Length in centimetres respectively, N is the number of turns. What this says is that the inductance increases with the square of the number of turns, but decreases linearily with the overall length of the winding.
If you didn't have the effect from the non-zero diameter, then you would get four times the inductance by increasing both the number of turns and the length four times.
Depending on how critical you think you need to know the inductance, you may have to play with the dimensions a bit to get exactly four times the current inductance.
Quote:
Originally Posted by Neil Purling
The point where both coils are tapped is around 1/13th of the total number of turns.
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That does sound a bit high. 1/20th to 1/30th is probably closer to optimum, perhaps even smaller, depending on how low losses your setup has.
On LW you may run into the small snag that a good regen detector will have too low bandwidth for good reproduction of an AM signal. If this happens, then you will notice this because the highs may be attenuated to some degree.
Frank N.