ferrites-question for Eric

[Anonymous]

Hi Eric,
can you please figure out, which ferrite form gives best results? - does it a long or short cilinder (which D/L ratio is best), ore an E-form from power transformer, or perhaps U-form?
thank you
Walter

 

[Anonymous]

Hi Walter,
Rods are the best for treasure hunting probes. The ones I use are 0.5in diameter but of various lengths depending on the detection range I want to achieve. They vary from 2in long to 8in long. As with a bar magnet, the field extends further with longer rods. Using an 8in rod, I can detect a coin at 10in with a medium power PI circuit. You can use U or E cores, or even 1/2 pot cores but the field will be much more localised and you wont get much range. These latter types are mainly used for industrial applications i.e. proximity sensors.
Eric.

 

[Anonymous]

many thanks Eric,
my next question is - do you use a coil as long as the rod (e.g.8in), or do you use a very short one, and - in the middle or at the "low" end of the rod?
thank you!
Walter

 

[Anonymous]

Hi Eric,
i checked Farnell and RS an Conrad - no rods to by. Do you have a hint for a supplier?
thank you
Walter

 

[Anonymous]

Hi Walter,
I wind the coil centrally on the rod. Depending on the rod length it can be one layer or two. The number of turns used being sufficient to give an inductance of about 300uH for most applications.
Eric.

 

[Anonymous]

Hi Walter,
The only place I know where you can buy suitable rods in small quantities is Pulsepower Developments i.e. me. Few companies make rods of suitable material and you often have to order 100's, if not 1000's, to get anyone interested. The only rods I have at present are 1/2in diameter x 2.75in long.
Eric.