Need help....Coil formula for ferrite rod

[George]

I have a ferrite rod out of a stereo L= 4.7" (119.9mm) X W= .39"
(9.95mm) I would like to make a loopstick antenna to detect lightning
strikes. Ideal tuning would be 40Khz, but that might take a mile of
wire. I am looking at around 400Khz. I need to wind a coil using
..014" (.34mm) magnetic wire. All I can find is formulas for aircoils.
Is there a formula or software for ferrite core coils or does it
matter?
I have not picked a cap yet for the tank circuit.
Thanks

 

[John Popelish]

I have a ferrite rod out of a stereo L= 4.7" (119.9mm) X W= .39"
(9.95mm) I would like to make a loopstick antenna to detect lightning
strikes. Ideal tuning would be 40Khz, but that might take a mile of
wire. I am looking at around 400Khz. I need to wind a coil using
.014" (.34mm) magnetic wire. All I can find is formulas for aircoils.
Is there a formula or software for ferrite core coils or does it
matter?
I have not picked a cap yet for the tank circuit.
Thanks

I don't understand why you want to tune the antenna. Lightning is an
impulse effect and is best captured with a broad band antenna. If the
antenna is untuned, the number of turns is not at all critical. you
can pass the signal through an audio amplifier and listen to the
lightning.

By the way, there are some nice, negative resistance opamp low
frequency receiver circuits available on the ULFELF, and VLF
discussion group files sections at Yahoo groups. Both these groups
deal with this sort of signal, as well as lots of other low frequency
energy sources.


By the way, windings over the middle third of the rod make best use of
flux passing through the rod. The outer thirds are essentially flux
concentrators (flux arriving from all around the rod), but all the
collected flux passes through the center section. It is very handy to
find a small spool that slides over the rod and just wind it about
full. Hobby and craft stores often sell small lots of colorful wire
on such small spools.

 

[George]

Future plan is to make a identical pair of (orthogonal) cross tuned
rods and a whip for the 180 degree shift for direction detection,
Just getting started

 

[John Popelish]

Future plan is to make a identical pair of (orthogonal) cross tuned
rods and a whip for the 180 degree shift for direction detection,
Just getting started

Perhaps this page will have some information you find useful:
http://www.amidoncorp.com/aai_ferriterods.htm

 

[George]

I did a search on Yahoo, found a project link to just what I wanted,
but as usuall another blank page. 100Khz to 450Khz. I looked at the
Url, may take me a day to figure out the formula. Would have thought
someone would have written a small program with fill in the blanks. I
may have to look for a longer ferrite rod, 12-15 inch.
Thanks for the URL

 

[John Popelish]

I may have to look for a longer ferrite rod, 12-15 inch.

Most antenna rods are optimized for medium wave band, not below .5
MHz. You can assemble a cheap, low frequency rod, by gluing together
low frequency ferrite beads made for EMI suppression. Go to Digikey,
search for [bead], then select [Ferrite Cores for Cables & Wiring,
EMI(108 items)] and then, under Series, select LFB. One of my
favorites is the 5/8" diameter LFB159079-000.

If you lap the ends with a bit of silicon carbide sand paper on a
sheet of glass, you will get a tiny improvement in effective
permeability. I have done lots of testing with an 11 inch rod made of
these beads, but the URL I pointed you towards indicates that the rod
should keep improving up to around 20 inches long, where diminishing
returns sets in.

 

[[email protected]]

I have a ferrite rod out of a stereo L= 4.7" (119.9mm) X W= .39"
(9.95mm) I would like to make a loopstick antenna to detect lightning
strikes. Ideal tuning would be 40Khz, but that might take a mile of
wire. I am looking at around 400Khz. I need to wind a coil using
.014" (.34mm) magnetic wire. All I can find is formulas for aircoils.
Is there a formula or software for ferrite core coils or does it
matter?
I have not picked a cap yet for the tank circuit.
Thanks

If I had the urge to build something along these lines, I'd work on
those lightning "about to strike" boxes. I never saw one myself, but I
understand there are devices that measure the potential of the air to
indicate a strike is likely.

The problem I see with building just one sensor for lightning strikes
is you really can't do a decent job detecting the distance. Now
multiple sensors and triangulation would be a different story. In fact,
it would be....
http://www.sord.nv.doe.gov/Lightning/Lightning-sord.htm

 

[Jim Thompson]

If I had the urge to build something along these lines, I'd work on
those lightning "about to strike" boxes. I never saw one myself, but I
understand there are devices that measure the potential of the air to
indicate a strike is likely.

The problem I see with building just one sensor for lightning strikes
is you really can't do a decent job detecting the distance. Now
multiple sensors and triangulation would be a different story. In fact,
it would be....
http://www.sord.nv.doe.gov/Lightning/Lightning-sord.htm

See...

http://www.sovereign-publications.com/global.htm

I did design work for Lightning Location and Protection (LLP), Tucson,
in the early '80's.

...Jim Thompson

 

[Homer J Simpson]

I have a ferrite rod out of a stereo L= 4.7" (119.9mm) X W= .39"
(9.95mm) I would like to make a loopstick antenna to detect lightning
strikes. Ideal tuning would be 40Khz, but that might take a mile of
wire. I am looking at around 400Khz.

A big aircoil might be better anyway - think a metre square. Those are used
as boosters for radios with ferrite rods.

 

[[email protected]]

Back several years ago, Scientific American Amateur Scientist presented a
design for just what you're looking for. IIRC they recommended strip
laminations, quite a bit longer than the normal ferrite rod. They gave an
address for a company that sells specially treated material with top grade
magnetic characteristics. They gave full details of the windings and
electronics, alrhough like a lot of their efforts at the latter, it's not
too hard to improve on it.

Your city library should have back issues. It was one of the last amateur
scientist articles, that may help you track it down.

I've seen the article--it's in the Amateur Scientist CD-ROM compiled
by Shawn Carlson.

Not being home I can't give the publication date, but do recall they
recommended steel reinforcing bar -- "rebar" -- for the core, and
something like 100,000 turns of fine wire, using this apparatus to
detect very low frequency changes in the Earth's magnetic field, as
well as responding to lightning, IIRC. The upgraded core material
(preferred, but more expensive) was mu-metal, with suggested suppliers
listed.

HTH,
James Arthur

 

[John Woodgate]

Not being home I can't give the publication date, but do recall they
recommended steel reinforcing bar -- "rebar" -- for the core, and
something like 100,000 turns of fine wire, using this apparatus to
detect very low frequency changes in the Earth's magnetic field, as
well as responding to lightning, IIRC. The upgraded core material
(preferred, but more expensive) was mu-metal, with suggested suppliers
listed.

Oh, that is utter rubbish! It's like the more extreme views of
audiophools.

If you have a magnetic core in the form of a rod, long compared with
its diameter, its own permeability only has a minor effect on its
inductance, because of the huge 'air-gap' in the magnetic circuit. And
asking for 1000000 turns is just making things needlessly difficult (and
expensive, of course).

 

[George]

Checked out the beads, $20.00 for two 11 inch stacked rods.
What size coil did you wrap around the middle of the stacked beads?
What kind of output did you get from the beads? Did you use an amp
after the output?
BIG question. What do you think Boltek is using that is so small in
there receiver?
http://www.boltek.com/stracker.htm
Thanks

I may have to look for a longer ferrite rod, 12-15 inch.

Most antenna rods are optimized for medium wave band, not below .5
MHz. You can assemble a cheap, low frequency rod, by gluing together
low frequency ferrite beads made for EMI suppression. Go to Digikey,
search for [bead], then select [Ferrite Cores for Cables & Wiring,
EMI(108 items)] and then, under Series, select LFB. One of my
favorites is the 5/8" diameter LFB159079-000.

If you lap the ends with a bit of silicon carbide sand paper on a
sheet of glass, you will get a tiny improvement in effective
permeability. I have done lots of testing with an 11 inch rod made of
these beads, but the URL I pointed you towards indicates that the rod
should keep improving up to around 20 inches long, where diminishing
returns sets in.

 

[George]

Checked out the beads, $20.00 for two 11 inch stacked rods.
What size coil did you wrap around the middle of the stacked beads?
What kind of output did you get from the beads? Did you use an amp
after the output?
BIG question. What do you think Boltek is using that is so small in
there receiver?
http://www.boltek.com/stracker.htm
Thanks

I may have to look for a longer ferrite rod, 12-15 inch.

Most antenna rods are optimized for medium wave band, not below .5
MHz. You can assemble a cheap, low frequency rod, by gluing together
low frequency ferrite beads made for EMI suppression. Go to Digikey,
search for [bead], then select [Ferrite Cores for Cables & Wiring,
EMI(108 items)] and then, under Series, select LFB. One of my
favorites is the 5/8" diameter LFB159079-000.

If you lap the ends with a bit of silicon carbide sand paper on a
sheet of glass, you will get a tiny improvement in effective
permeability. I have done lots of testing with an 11 inch rod made of
these beads, but the URL I pointed you towards indicates that the rod
should keep improving up to around 20 inches long, where diminishing
returns sets in.

 

[Adrian Jansen]

I have a ferrite rod out of a stereo L= 4.7" (119.9mm) X W= .39"
(9.95mm) I would like to make a loopstick antenna to detect lightning
strikes. Ideal tuning would be 40Khz, but that might take a mile of
wire. I am looking at around 400Khz. I need to wind a coil using
.014" (.34mm) magnetic wire. All I can find is formulas for aircoils.
Is there a formula or software for ferrite core coils or does it
matter?
I have not picked a cap yet for the tank circuit.
Thanks

For rule-of-thumb, the rod permeability is of the order length/diameter.
Since this rarely exceeds 20 or so, then this controls the permeability,
since the material permeability is of the order 200 or so for most
ferrite rods used for antennas.

So just use your air-core formula, and multiply by l/d for an initial
guess on the inductance.

--
Regards,

Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.

 

[John Popelish]

Checked out the beads, $20.00 for two 11 inch stacked rods.
What size coil did you wrap around the middle of the stacked beads?

Lots of variations from a few turns to hundreds. Some of the test
data is presented in the files section of the
ferriterodantennaexperimenters Yahoo group.

What kind of output did you get from the beads? Did you use an amp
after the output?

I just tested rod and coil combinations for Q with an antique Q meter.

BIG question. What do you think Boltek is using that is so small in
there receiver?
http://www.boltek.com/stracker.htm

Don't know, but I think they are over charging for it.

 

[Bruce Varley]

I have a ferrite rod out of a stereo L= 4.7" (119.9mm) X W= .39"
(9.95mm) I would like to make a loopstick antenna to detect lightning
strikes. Ideal tuning would be 40Khz, but that might take a mile of
wire. I am looking at around 400Khz. I need to wind a coil using
.014" (.34mm) magnetic wire. All I can find is formulas for aircoils.
Is there a formula or software for ferrite core coils or does it
matter?
I have not picked a cap yet for the tank circuit.
Thanks

Back several years ago, Scientific American Amateur Scientist presented a
design for just what you're looking for. IIRC they recommended strip
laminations, quite a bit longer than the normal ferrite rod. They gave an
address for a company that sells specially treated material with top grade
magnetic characteristics. They gave full details of the windings and
electronics, alrhough like a lot of their efforts at the latter, it's not
too hard to improve on it.

Your city library should have back issues. It was one of the last amateur
scientist articles, that may help you track it down.

 

[[email protected]]

Oh, that is utter rubbish! It's like the more extreme views of
audiophools.

If you have a magnetic core in the form of a rod, long compared with
its diameter, its own permeability only has a minor effect on its
inductance, because of the huge 'air-gap' in the magnetic circuit. And

Of course. I believe the rod was 1-meter-ish long, but don't recall
the thickness.

asking for 1[,]000[,]000 turns is just making things needlessly difficult (and
expensive, of course).

It may have "only" been 50,000 turns, but not 1,000,000! Either way,
a lot of wire, and quite a bit of stray capacitance, choking off the
usable bandwidth.

The "low noise" amplifier for this pickup was something like an
OP-07, inverting, with a 1k input and 100k feedback resistor. Oh well
! (I'll post the particulars when I get home to access it.)

Even so, its builders reported having all sorts of fun with it, which
is what matters most, yes?

Best,
James Arthur

 

[Bruce Varley]

I have a ferrite rod out of a stereo L= 4.7" (119.9mm) X W= .39"
(9.95mm) I would like to make a loopstick antenna to detect lightning
strikes. Ideal tuning would be 40Khz, but that might take a mile of
wire. I am looking at around 400Khz. I need to wind a coil using
.014" (.34mm) magnetic wire. All I can find is formulas for aircoils.
Is there a formula or software for ferrite core coils or does it
matter?
I have not picked a cap yet for the tank circuit.
Thanks

Back several years ago, Scientific American Amateur Scientist presented a
design for just what you're looking for. IIRC they recommended strip
laminations, quite a bit longer than the normal ferrite rod. They gave an
address for a company that sells specially treated material with top grade
magnetic characteristics. They gave full details of the windings and
electronics, alrhough like a lot of their efforts at the latter, it's not
too hard to improve on it.

Your city library should have back issues. It was one of the last amateur
scientist articles, that may help you track it down.