My Crystalset "DoubleDutch"
The result of my first experiments with Moebius coils.
The name of this set may give you the idea that I am trying to make a fool of you, but you may rest assured that I am only referring to the double tuning system and to my nationality!
All coils used in "DoubleDutch" are wound on a single large ferrite core (T200), salvaged from a Drake 1kW Balun type B-1000.
The 2 Moebius windings (L2 & L3) are wound directly on the core (Teflon insulated wire).
Each of the windings is 178 microHenry and together, put in series, they form a Moebiuscoil of 140 microHenry. This coil is used as part of the detector tuning circuit
On top of this coil is a normal winding, with 3 taps (L1).
This coil is part of a circuit that makes it possible to tune the antenna in a series or parallel configuration.
To explain the way I wound the Moebiuscoil, I made a second core, as an example, with 2 windings of only 3 turns and added a photo of this second coil to the photo collection of this project.
As I already used the only dialknob in my possession for my Crystal set "Dutchie", I glued an old free CD upside down under a knob and drilled a 10mm hole in it. The scale was made with the help of MS-Excel and PhotoShop.
To descibe the results I can honestly say that I have never before heard so many stations so clearly out of a Crystal set.
The Q of the Moebiuscoil must be high (I am sorry to say that I do not have the means to measure the Q) because the selectivity is enough using an antenna of about 28 meters long in spite of the very tight magnetic coupling between the coils.
May the best design win, good luck to all fellow contestants,
Wim van Leeuwen
(Dutch Ham: PA3CAY, Yahoo Crystal Set Radio Club: Coherer2000)