Ferrite Rods - question for Eric

[Anonymous]

Hi Eric,
I am interested to experiment with PI search coils on exceptionally long ferrite rods (>=8in long), hoping for deeper range.
Could I use a ferrit antenna from a SW-radio? - do you know, if such rods can be used with short sample delays (<10us)?
What are the output power limitations?
Or do you know a source for low quantities?
Or can you tell me the criteria for suitable rods to ask for by different suppliers in Germany?
I thank you for your time and also for the support you give all
of us hobbyists within your classroom.
best regards
Walter Marton

 

[Anonymous]

Hi Walter,
There are many ferrite rods available from various manufacturers, but I haven't looked to see what is available for some time. There are two main types - soft ferrites and hard ferrites. These qualities refer to the magnetic characteristics rather than physical. The type that works with a PI is a soft ferrite and is the same as used in transformer cores for high power switch mode power supplies. Soft ferrites come in many grades and it is best to request a sample to try. Some do not work because they are microphonic, or exhibit mechanical ringing.
The rods that are used in radio antennas are not suitable as they give a long magnetic decay; similar to iron mineralised ground. Seems to be a contradiction, since they work at r.f., but that is the case in the rods I have tested.
I you find anyone that makes long rods, let me know.
Eric.

 

[Anonymous]

Eric, what size rods both length and dia. were you interested in? Or what is the characteristic that you think would be interesting to test? Could a rod wraped in litz wire recieve as well as a coil? I saw on another site some time ago the mention that mild 1020 steel was used in a way as to make a magnetic lens and that the steel did not show negative characteristic of noise. The learning curve here is very steep and most goes over my head as I am just getting started,but what a ride.

 

[Anonymous]

Hi all. I learned that most of convenient ferrite materials are ringing. The exponential decay is jagged with constant frequency, order of ten kilohertzes. The aplitude of this modulation depends on current and the frequency changes with lenght of the rod. It is apparently mechanic effect - magnetostriction. The only way to get rid of it is to compose the rod of smaller pieces of different lenght and glue together. Nice day, Sid.

 

[Anonymous]

Hi Wyndham,
Once I had some rods that were 8in long x 1/2in diameter. These worked well and gave a similar range on a coin to a 6in coil. I also had a few rods that were 3/4in diameter, and you could pulse them with a higher current to get more range. Above a certain current the rods start to ring severely (magnetic saturation?) and stop functioning correctly. Some, also are sensitive to their orientation in the earth's magnetic field, and give false signals if you wave them about. It is an area that has not been thoroughly researched yet as to which ferrite is best for the job.
I've never wound a rod with Litz wire, so I don't know if there would be any benefit.
I have not come across any metallic steel that would work, because of its conductivity.
Eric.

 

[Anonymous]

Eric: I found a site that has ferrite rods that are I think a crushed ceramic ferrite material and put into a plastic tube. Quote frome the site "SLF Ferrite rods are made from a blend of brittle ceramic materials that act like molecule-sized magnetic field amplifiers. It is easy to use an SLF ferrite rod as a sensor for weak magnetic fields. Just wind copper wire on the outside of the rod." http://www.stormwise.com/vlf.htm
Is this a possibility? They have 2 types of rods slf & vlf
the reson I asked about the litz wire is how else would you get the tx/rx signal to the pi box. Would you attach a lead to each end? Sorry to be a bit slow on this but just learning. Wyndham