How long the ferrite rod?

R

Richard

Guest
Hi.

I'm wanting to exchange "air cored" frame aerials for ferrite rods, for the
medium waveband (Broadcast band).

The ferrite rods are 10mm dia, and the MW coil for it is 35mm long, I think
about 90 turns. Now, how long should the ferrire rods be do you think? The
thing is, I've got some fairly long rods (200mm long) and I'm thinking
should I cut the rods so they are say 100mm long or even 66.66mm long. The
point is, does it matter that much how long the ferite rod is? Could I in
fact use a 66.66mm rod and it would be no better or worse than a 100mm rod?

Also, how do you cut a ferrite rod? TIA.
 
"Richard" <notty@emailo.com> wrote in message
news:3epivdF4ankvU1@individual.net...
Hi.

I'm wanting to exchange "air cored" frame aerials for ferrite rods, for
the
medium waveband (Broadcast band).

The ferrite rods are 10mm dia, and the MW coil for it is 35mm long, I
think
about 90 turns. Now, how long should the ferrire rods be do you think? The
thing is, I've got some fairly long rods (200mm long) and I'm thinking
should I cut the rods so they are say 100mm long or even 66.66mm long. The
point is, does it matter that much how long the ferite rod is? Could I in
fact use a 66.66mm rod and it would be no better or worse than a 100mm
rod?

Also, how do you cut a ferrite rod? TIA.
Click to expand...
Actually I bet it's good to have no less than 4" (100mm), so if I do cut
I'll not cut shorter. No idea whether there is much advantage to rod being
longer.
 
Richard wrote:
"Richard" <notty@emailo.com> wrote in message
news:3epivdF4ankvU1@individual.net...

Hi.

I'm wanting to exchange "air cored" frame aerials for ferrite rods, for

the

medium waveband (Broadcast band).

The ferrite rods are 10mm dia, and the MW coil for it is 35mm long, I

think

about 90 turns. Now, how long should the ferrire rods be do you think? The
thing is, I've got some fairly long rods (200mm long) and I'm thinking
should I cut the rods so they are say 100mm long or even 66.66mm long. The
point is, does it matter that much how long the ferite rod is? Could I in
fact use a 66.66mm rod and it would be no better or worse than a 100mm

rod?

Also, how do you cut a ferrite rod? TIA.



Actually I bet it's good to have no less than 4" (100mm), so if I do cut
I'll not cut shorter. No idea whether there is much advantage to rod being
longer.

The longer the rod, the bigger volume of space it couples into, and
Click to expand...
the more energy it might intercept from the waves passing through that
volume. This generality applies to any length much shorter than 1/4
wavelength.
 
"John Popelish" <jpopelish@rica.net> wrote in message
news:7b6dnRohoLrYLxrfRVn-ow@adelphia.com...
Richard wrote:
"Richard" <notty@emailo.com> wrote in message
news:3epivdF4ankvU1@individual.net...

Hi.

I'm wanting to exchange "air cored" frame aerials for ferrite rods, for

the

medium waveband (Broadcast band).

The ferrite rods are 10mm dia, and the MW coil for it is 35mm long, I

think

about 90 turns. Now, how long should the ferrire rods be do you think?
The
thing is, I've got some fairly long rods (200mm long) and I'm thinking
should I cut the rods so they are say 100mm long or even 66.66mm long.
The
point is, does it matter that much how long the ferite rod is? Could I
in
fact use a 66.66mm rod and it would be no better or worse than a 100mm

rod?

Also, how do you cut a ferrite rod? TIA.



Actually I bet it's good to have no less than 4" (100mm), so if I do cut
I'll not cut shorter. No idea whether there is much advantage to rod
being
longer.

The longer the rod, the bigger volume of space it couples into, and
the more energy it might intercept from the waves passing through that
volume. This generality applies to any length much shorter than 1/4
wavelength.
Click to expand...
I suppose there is a formula somewhere showing output volts against length.
 
Hi,

"Seek and ye shall find", Mathew 7:7

Or read the two "Ferrite Rods Bars Plates" PDFs on this site.

http://www.cwsbytemark.com/CatalogSheets/spec_sheets.php


Cheers - Joe

P.S For maximum induced volts, use the entire rod.
 
"Joe McElvenney" <ximac@btinternet.com> wrote in message
news:VA.00000101.001ea9ea@btinternet.com...
Hi,

"Seek and ye shall find", Mathew 7:7

Or read the two "Ferrite Rods Bars Plates" PDFs on this site.

http://www.cwsbytemark.com/CatalogSheets/spec_sheets.php


Cheers - Joe

P.S For maximum induced volts, use the entire rod.
Click to expand...
Thanks.

So, I beleive the formula I'm looking for is:

Loop Induced Voltage (Fhe) = 2πNAµeF
__________ (in ÂľV)
Îť
Anyway as per:

http://www.cwsbytemark.com/cws_catalog/section2/2_31_rods_bars_plates2.pdf

And as you point out, for maximum induced volts use the entire rod.
 
On Sun, 15 May 2005 22:30:35 +0100, "Richard" <notty@emailo.com>
wrote:

"John Popelish" <jpopelish@rica.net> wrote in message
news:7b6dnRohoLrYLxrfRVn-ow@adelphia.com...
Richard wrote:
"Richard" <notty@emailo.com> wrote in message
news:3epivdF4ankvU1@individual.net...

Hi.

I'm wanting to exchange "air cored" frame aerials for ferrite rods, for

the

medium waveband (Broadcast band).

The ferrite rods are 10mm dia, and the MW coil for it is 35mm long, I

think

about 90 turns. Now, how long should the ferrire rods be do you think?
The
thing is, I've got some fairly long rods (200mm long) and I'm thinking
should I cut the rods so they are say 100mm long or even 66.66mm long.
The
point is, does it matter that much how long the ferite rod is? Could I
in
fact use a 66.66mm rod and it would be no better or worse than a 100mm

rod?

Also, how do you cut a ferrite rod? TIA.



Actually I bet it's good to have no less than 4" (100mm), so if I do cut
I'll not cut shorter. No idea whether there is much advantage to rod
being
longer.

The longer the rod, the bigger volume of space it couples into, and
the more energy it might intercept from the waves passing through that
volume. This generality applies to any length much shorter than 1/4
wavelength.

I suppose there is a formula somewhere showing output volts against length.
Click to expand...
---
Click on this:

http://www.google.com/search?hl=en&q=ferrite+antenna

and then on the first hit you get, and it may lead you here:

http://home.att.net/~ray.l.cross/murod_mm/


You'll need a diamond saw or a CO2 laser to cut the rods.

--
John Fields
Professional Circuit Designer
 
On Sun, 15 May 2005 19:35:05 +0100, Richard wrote:

Hi.

I'm wanting to exchange "air cored" frame aerials for ferrite rods, for
the medium waveband (Broadcast band).

The ferrite rods are 10mm dia, and the MW coil for it is 35mm long, I
think about 90 turns. Now, how long should the ferrire rods be do you
think? The thing is, I've got some fairly long rods (200mm long) and I'm
thinking should I cut the rods so they are say 100mm long or even 66.66mm
long. The point is, does it matter that much how long the ferite rod is?
Could I in fact use a 66.66mm rod and it would be no better or worse than
a 100mm rod?

Also, how do you cut a ferrite rod? TIA.
Click to expand...
If it's powdered iron, you can cut it with a diamond saw. If it's
ferrite, you probably can't cut it, but there's a possibility you
could score it with a triangular file and snap it, like glass
tubing.

Good luck!
Rich
 
On Mon, 16 May 2005 18:13:23 GMT, Rich Grise <richgrise@example.net>
wrote:

On Sun, 15 May 2005 19:35:05 +0100, Richard wrote:

Hi.

I'm wanting to exchange "air cored" frame aerials for ferrite rods, for
the medium waveband (Broadcast band).

The ferrite rods are 10mm dia, and the MW coil for it is 35mm long, I
think about 90 turns. Now, how long should the ferrire rods be do you
think? The thing is, I've got some fairly long rods (200mm long) and I'm
thinking should I cut the rods so they are say 100mm long or even 66.66mm
long. The point is, does it matter that much how long the ferite rod is?
Could I in fact use a 66.66mm rod and it would be no better or worse than
a 100mm rod?

Also, how do you cut a ferrite rod? TIA.

If it's powdered iron, you can cut it with a diamond saw. If it's
ferrite, you probably can't cut it, but there's a possibility you
could score it with a triangular file and snap it, like glass
tubing.
Click to expand...
---
A diamond saw will cut ferrite, since diamond is harder than ferrite.

--
John Fields
Professional Circuit Designer
 
Rich Grise wrote:
On Sun, 15 May 2005 19:35:05 +0100, Richard wrote:


Hi.

I'm wanting to exchange "air cored" frame aerials for ferrite rods, for
the medium waveband (Broadcast band).

The ferrite rods are 10mm dia, and the MW coil for it is 35mm long, I
think about 90 turns. Now, how long should the ferrire rods be do you
think? The thing is, I've got some fairly long rods (200mm long) and I'm
thinking should I cut the rods so they are say 100mm long or even 66.66mm
long. The point is, does it matter that much how long the ferite rod is?
Could I in fact use a 66.66mm rod and it would be no better or worse than
a 100mm rod?

Also, how do you cut a ferrite rod? TIA.


If it's powdered iron, you can cut it with a diamond saw. If it's
ferrite, you probably can't cut it, but there's a possibility you
could score it with a triangular file and snap it, like glass
tubing.
Click to expand...
But unless you need to shorten it for reasons other than reception
quality, there is little reason to shorten it. The only reason radios
don't come with foot long ferrite rods is cost and overall unit
miniaturization.
 
On Mon, 16 May 2005 17:55:59 -0400, John Popelish <jpopelish@rica.net>
wrote:

Rich Grise wrote:
On Sun, 15 May 2005 19:35:05 +0100, Richard wrote:


Hi.

I'm wanting to exchange "air cored" frame aerials for ferrite rods, for
the medium waveband (Broadcast band).

The ferrite rods are 10mm dia, and the MW coil for it is 35mm long, I
think about 90 turns. Now, how long should the ferrire rods be do you
think? The thing is, I've got some fairly long rods (200mm long) and I'm
thinking should I cut the rods so they are say 100mm long or even 66.66mm
long. The point is, does it matter that much how long the ferite rod is?
Could I in fact use a 66.66mm rod and it would be no better or worse than
a 100mm rod?

Also, how do you cut a ferrite rod? TIA.


If it's powdered iron, you can cut it with a diamond saw. If it's
ferrite, you probably can't cut it, but there's a possibility you
could score it with a triangular file and snap it, like glass
tubing.
Click to expand...
---
Except, perhaps, for the central void.
---

But unless you need to shorten it for reasons other than reception
quality, there is little reason to shorten it. The only reason radios
don't come with foot long ferrite rods is cost and overall unit
miniaturization.
Click to expand...
---
Kinda like transformers?


--
John Fields
Professional Circuit Designer
 
John Fields wrote:

But unless you need to shorten it for reasons other than reception
quality, there is little reason to shorten it. The only reason radios
don't come with foot long ferrite rods is cost and overall unit
miniaturization.

Kinda like transformers?
Click to expand...
Not really. Transformers are made as small and cheap as possible, but
making them very much larger than necessary does not add much but
weight. Making a rod antenna much larger (besides making it more
costly) also provides lots more signal.
 
John Popelish wrote:
John Fields wrote:

But unless you need to shorten it for reasons other than reception
quality, there is little reason to shorten it. The only reason
radios don't come with foot long ferrite rods is cost and overall
unit miniaturization.


Kinda like transformers?


Not really. Transformers are made as small and cheap as possible, but
making them very much larger than necessary does not add much but
weight. Making a rod antenna much larger (besides making it more
costly) also provides lots more signal.
Click to expand...
I am also pretty sure that gluing a large ferrite bead (like those
around power cords for RFI suppression) on each end of the rod, beyond
the winding, also gets you some extra signal. No need to have the
bead hole filled with the rod. Just a bit of overlap works.
 
On Mon, 16 May 2005 17:55:59 -0400, John Popelish wrote:

Rich Grise wrote:
On Sun, 15 May 2005 19:35:05 +0100, Richard wrote:


Hi.

I'm wanting to exchange "air cored" frame aerials for ferrite rods, for
the medium waveband (Broadcast band).

The ferrite rods are 10mm dia, and the MW coil for it is 35mm long, I
think about 90 turns. Now, how long should the ferrire rods be do you
think? The thing is, I've got some fairly long rods (200mm long) and I'm
thinking should I cut the rods so they are say 100mm long or even
66.66mm long. The point is, does it matter that much how long the ferite
rod is? Could I in fact use a 66.66mm rod and it would be no better or
worse than a 100mm rod?

Also, how do you cut a ferrite rod? TIA.


If it's powdered iron, you can cut it with a diamond saw. If it's
ferrite, you probably can't cut it, but there's a possibility you could
score it with a triangular file and snap it, like glass tubing.

But unless you need to shorten it for reasons other than reception
quality, there is little reason to shorten it. The only reason radios
don't come with foot long ferrite rods is cost and overall unit
miniaturization.
Click to expand...
Yeah, I read the other responses saying pretty much the same thing
about an ohnosecond or three after I posted. :)

Thanks!
Rich
 
On Mon, 16 May 2005 23:05:57 -0400, John Popelish wrote:

John Popelish wrote:
John Fields wrote:

But unless you need to shorten it for reasons other than reception
quality, there is little reason to shorten it. The only reason radios
don't come with foot long ferrite rods is cost and overall unit
miniaturization.


Kinda like transformers?


Not really. Transformers are made as small and cheap as possible, but
making them very much larger than necessary does not add much but
weight. Making a rod antenna much larger (besides making it more
costly) also provides lots more signal.

I am also pretty sure that gluing a large ferrite bead (like those
around power cords for RFI suppression) on each end of the rod, beyond the
winding, also gets you some extra signal. No need to have the bead hole
filled with the rod. Just a bit of overlap works.
Click to expand...
Back when I was in the USAF, I stole a 4-400A by checking it out of
bench stock, and watched a guy build a nominally kilowatt linear out
of that and a bunch of surplus crap. This was in Okinawa (early 1970's),
and you couldn't walk down the street without passing a couple of surplus
dealers. He did it grounded-grid, and for his filament choke, he took
about a half-dozen tuning slugs from various coils, transformers, etc -
but these were big fat tuning slugs - about 3/4" diameter and about 1"
long. He just glued them together. He had found a beautiful silver-plated
coil for the pi-net output, and of course, it was covered with tarnish.
I thought he should have just wiped a little Brasso on it, but this idiot
SANDPAPERED it! AAAAIIIIEEEEeeeee! Later, I came to find out that silver
tarnish not only doesn't hurt in that situation, but might actually
be beneficial! But SANDPAPER! Well, it was only HF, and I'm sure that
wasn't the only ineffeciency with the thing. But he did DX with it.
I have to admit, it was kinda cool seeing the plate go bright orange
until he got it tuned properly. :) And it hissed. Somebody told me
that that was the ka-dink effect. The electrons hit the plate so hard
and fast, that they knock off secondary electrons, which when they
hit the glass, go "ka-dink!" ;-)

Cheers!
Rich
 
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