Ferrite Rods (or work alikes)

"phaeton"

** No, must be ferrite.

Get then nothing out of any discarded transistor radio, cassette radio or clock radio.

........ Phil

A bolt probably won't work. Eddy currents in the bolt would eat up a lot of the energy making the range low assuming the transmitter portion oscillated at all.

You do have some options however. Assuming you can't find some ferrite rod material, you can stack a series of toroids or ferrite beads together and treat it like a rod (use a dowel or nonconductive center or just glue them together)

It oscillates at 35 KHZ which is relatively low and you could probably get by with a bunch of thin iron wire. The iron should not conduct well, so allow it to rust a little before packing the core.

I use steel fence (agricultural electric fence) wire for wire cores since it is readily available and cheap. It is zinc coated to prevent rusting and is very conductive. I cut the wires to the length I need for my core then put them in a jar of vinegar for a few days - that causes the zinc to oxidize and insulates the wires. I neutralize the acid with a rinse of baking soda.

Craft stores are another source of thinner steel wire - but they can be costly if you need a large core.

Alternatively you can just chuck them in a fire and burn the coating off - the zinc vapor may be toxic so you'd want to avoid doing it where you breath or under the chicken in the BBQ grill . . . Burning it will or may cause it to anneal and that is desirable in a magnetic core (easier to bend or straighten too)

You can make your own powdered iron cores that will work really well. I started fooling with steel wool in an attempt to make a high frequency core - it actually worked pretty well.

You can make a core to rival commercial ones by buying fine iron powder - stay away from science shops, it costs too much - it is for sale on line for pyrotechnic purposes in different sieve numbers (particle sizes). Stuff is used to make bright white star burst fireworks shells and roman candles.

My technique is to mix the powdered iron with epoxy thinned with a smidgen of acetone (or get thin boat builders epoxy or polyester resin) then pour it into a short length of PVC or CPVC pipe that has been waxed inside with a coating of silicon grease as a mold release.

Pour it and cap it on both ends with greased PVC end caps pushed on, store it vertically while the epoxy sets - or you will regret it - one end cap will leave a shoulder in the molded product - it won't come out from that side. Let harden for a day or two then push the iron out (a dip in a pan of boiling water will help if it doesn't just slide out - most won't with PVC, CPVC is smoother inside).

Voilà! a powdered iron core that didn't cost a mint.

A further refinement is to stack ring type ferrite magnets around the mold while it hardens (stack has to be full length and you may have to grind off the shoulder on top before you push it out)

I have a lot of old speaker magnets that work well for that - but winding a coil and passing current through it may also work.

Magnets increase the permeability of the core by aligning the particles of iron while it sets up. They also tend to cause the mixture inside to try to walk out of the tube - so be sure to use two end caps pushed on hard.

It may work to just stuff a tube with iron powder and glue the caps on

- I don't know. The wall thickness of the tube may work against you for leakage inductance and the particles may move around while being excited by the driver - I assume that would be a bad thing but I haven't tried it.

cool circuit - haven't built it

--

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Fence wire is high-tensile, I'd expect softer wire, like tie wire to work better.

pre-rusted tie wire can be had cheap at places that sell steel for concrete reinforcing.

a coating of lacquer may work better than just trusting the rust to insulate it.

To straigtten short lengths of wire roll them between two flat MDF boards.

Bye. Jasen

Buy cheap radios from Wal-Mart and rob parts from them.

Yeah, annealed (soft) wire is better for transformer hysteresis. Leaving it in the charcoal grill and shutting the vents to kill the fire works like a champ to anneal, remove the zinc, and oxidize it .

Easier to work with the stiff wire if one is stuffing a tube to capacity. Likewise, uncoated or oiled wire is easier to pack than varnished wire.

Tie wire sounds good, I have to check that out. Bailing wire is pre-rusted or has a black oxide coating from the factory - but who needs 80 pound coils of the stuff? Fence wire is only $5 for a 1/4 mile and there must be ten-fifteen pounds on the spools. Really handy around the house too.

Back when I was experimenting with induction coil cores, I stretched the wire between trees with a come-along (cable hoist) and ran a series of offset pulleys up and down the wire - that straightened it pretty well. You can also buy wire for suspended ceiling "T" bar in bundles of straight lengths 10 feet long.

My first attempt at powdered iron was to feed steel wool through a hammer mill style garden leaf shredder. What a fiasco! It worked but tended to "pill" clumps of compressed wool. You wouldn't believe how far the stuff travels - the next day the clothes I wore and side of the house and deck had rust stains.

--

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

I have made many ferrite rods by assembling long form ferrite beads into a stack. At 35 kHz, the Steward LFB material would work just fine, and Digikey sells many sizes for little money. Buy beads of the appropriate diameter and epoxy them together.

Excellent, you guys.

As far as using wire to make an inductor, how about putting pieces in a plastic drinking straw for insulation? Work? No?

As far as epoxying a bunch of beads together, does there need to be anything in the middle of them? Maybe just a plastic bolt to mount them somewhere with?

Now (the big question)

Which has a higher effect on the 'coarse tuning' of the inductor:

1) Number of turns of wire. 2) Length of ferrite core. 3) Diameter of ferrite core. 4) Other

I realize that radios are 'fine tuned' with a variable capacitor. I know this is also not a very simple answer, so pointers to data is appreciated.

Also, the transmitter circuit calls for 3V-9V operation. If I were to modify the circuit for 18V-24V operation, would that increase its range?

Thanks!

-phaeton

Sure, but not really needed. The ferrite is not a very good conductor. and the signal voltage is low, so the wire insulation is plenty.

Nothing needed, but almost anything will work. Even a metal bolt, since most of the flux will pass parallel to it through the ferrite.

Proportional to almost turns squared, for turns in the middle third of the rod.

Almost proportional to length.

Less than proportional.

Location of turns on rod. Higher inductance for turns near center of rod, so fine adjustment by sliding the rod off center.

If nothing burned up, probably. I would go with a longer rod, though.

** You have completely misconstrued the OP's words.

Tell the PITA troll to get his ferrite rods from old radio and shut the f*ck up.

....... Phil

Sorry to hear about the pain in your ass.

Mine feels just fine.

** Misconstruing is your only forte.

Piss head.

........ Phil

At least I'm good at something.

By the way, do you care to tell why you are so angry so much of the time? Are you here to because you are angry, or in spite of being angry?

** Misconstruing is your only forte.

Piss head.

** Misconstruing is your only forte.

Piss head.

** Misconstruing is your only forte.

Piss head.

So fuuuuck the hell off.

....... Phil

Phil Allison wrote: (snip)

Get used to disappointment.

** Misconstruing is your only forte.

Piss head.

You'll be dead soon.

....... Phil

Of course, as shall we all.

I'm surprised you haven't placed Phil in your ignore list John....

I never see anything from him unless it's copied.

(snip)

I can't turn away from train wrecks, either.

"Lord Garth"

** Bugger off - you worthless tenth wit.

...... Phil