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.
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,..to 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 250µh
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.
PA2MRX © 2013