The "Toroidyne"

After a few crystal radio`s and some regenerative receivers I thought it was a good idea to build a crystal radio using some ferrite cores. I already had some lying around from earlier experiments about measureing the inductance in combination with the Q of the coils.  You need lesser windings on a ferrite core to get the inducance you need.  And hopefully this also rises the Q of the coils. We`ll see what bandwidth we get out of this little radio.

Here above the in Version A the receiver as I planned it. Connected it this way it did not receive the AM-BCB (531-1600Khz) but it received somewhere in the SW region of 5-7Mhz. I do not have a clue why.
So I re soldered some wires to change the setup to Version B. Now the crystal radio received the AM-BCB, but at evenings the sound of the big locals were very faint.  So I went to completely re-design the coupling of the two toroids. First I wound 16 windings between the litz  windings of each toroid. Tapped at every second winding, these taps should go to the selector switches and then go to the coupler toroid as seen in Version C.  But now I got an extra toroid just wasting some power. So I opted to completely delete the coupler toroid and connect the two pickup coils on the two toroids directly to the selector switches, as in Version Ca.

Coupling toroid with taps on top of my little finger.

Layout of the "Toroidyne" The front panel is brownish transparant plexiglass.
The base is hard wood and the sides got a nice finish milled on it.

With the radio now almost connected as in Version Ca,  almost, because I connected the two coupler windings on the two toroids directly 1:1 together, I started to give the receiver a test. Connected the antenna and ground to the fahnenstock clips. The reception was loud, loud, the big transmitters were all over the scale.  With no ground it was better, so I put in an extra 10pF capacitor to the ground fahnestock clip and connected the ground again. The selectivity went up an almost 1000%. So time to listen for some stations that evening.  Below the log of stations received on Febr.23 - 2013.  (R5 = perfect copy)


In the middle the Bogen T725 with impedance selector switches, M2 screws. And the two toroids 4C65 (FT140-61) of approx 250h inductance, using 240/48 litz wire on the antenna coil and 160/48 litz on the detector coil. Both toroids have in the above picture 16 windings of 0,75mm thick enameled copper wire. These have to go to the selector switches as in schematic Version Ca. The selector switches are double deck ceramic switches. One deck not used, so these windings go there. When the radio is "finished" I can take out the FT82-61 toroid, not in use anymore in this setup.

coupling coils being connected. The cut off wires from the Bogen T725 being re-used.

Looks good, the brown-ish transparant plexiglass front with clear plexiglass sides.
Wood used is Red Seraya.


PA2MRX 2013