this evening I had some free time to spend for starting my very
simple tests with ferrite rods. Picture 1 in the attached zip file
shows one of the rods (about 10mm diameter x 200mm long) together with
a short piece of plastic tube that I have used to adapt the rods to a
larger-diameter slotted aluminium tube - shown in picture 2. As you can
see, the longitudinal cut on the tube is not really regular and
"clean". I'm not very good at working with metals. Nevertheless, I hope
it will do the job, that is acting as a shield between the rods and the
coil. Picture 3 shows two of the three rods I used, each inserted in a
short piece of plastic pipe and protected with heat shrink tube and
some masking tape.
Finally, picture 4 shows the very provisional setup that I used
to try measuring Q of an LC pair composed by a 2-gangs variable
capacitor plus a 55-turns coil wound over the aluminium tube containing
the ferrite rods. I performed several measures, with 1, 2 or 3 rods
inside the tube. I saw that using 3 rods increases the inductance
significantly. For example, at an intermediate position of the varcap,
resonance was at 1037KHz with only 1 rod inside the tube, but it was at
767 KHz with 3 rods.The Q value also increases slightly using 3 rods,
even thought in my tests I got only a miserable figure of about 30.
Anyway, I decided to go with 3 rods for my next step, that will be to try Litz wire for the coil and
see what happens.
Note: pics 3 and 4
will be attached to a re-sent of this message.
Regards
D.
