Re: LF: Re: My first ferrite experiments

[Daniele Tincani <danieletincani@yahoo.com>]

Hello Stefan,

 

> but maybe the Q is reduced by the aluminium shield!

Do you think the aluminium could be the problem or the distance between the coil and the core? I could replace the aluminium tube with a plastic tube, if shielding is not necessary, but this would not improve the Q if the problem is the gap between the coil and the core.

 

> Are the rods galvanically separated from each other by a thin plastic tape? What type is the ferrite material?

Yes I put two layers of plastic tape on tips of each rod. The ferrite material is russian MU400HH.

 

Best regards

Daniele

 

Da: Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>
A: rsgb_lf_group@blacksheep.org
Inviato: Martedì 27 Settembre 2011 13:48
Oggetto: Re: LF: Re: My first ferrite experiments

Hello Daniele,

Nice work and good equipment.
I would suggest to make the wires between coil and cap as short as possible and not to use these crocodile clamps. HF litz wire should help about the Q but maybe the Q is reduced by the aluminium shield! Are the rods galvanically separated from each other by a thin plastic tape? What type is the ferrite material?

73, Stefan/DK7FC

PS: Tell me if you need a test signal ;-)

Am 27.09.2011 12:33, schrieb Daniele Tincani:

Pics 3 and 4 are attached here.

 

Da: Daniele Tincani <danieletincani@yahoo.com>
A: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Inviato: Martedì 27 Settembre 2011 12:31
Oggetto: My first ferrite experiments

 

Hello LF,

 

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.