Re: Working with shorter (and cheaper) ferrites - The Backpack FSL

Michael <michael.setaazul@...>

Thanks for your detailed consideration of this, Kevin.
It confirms what I half-assumed, but wasnt sure of.
I hadnt thought of the opposing "grain" of ferrite rings
as compared to rods or bars, which may well be

Early on in the FSL discussion, we briefly mentioned
the coil-diameter issue and the assumed simplified
underlying principle that the ferrite allows the loop
to be reduced in size for similar performance. It would
be interesting to experiment with a, say, 12inch loop
and different arrays of "lumped" ferrite inside, which would
doubtless be inferior to the best FSL designs, but might
give additional insight into viable variants.

Is Chinese ferrite available? Quality? Price?

Michael UK

----- Original Message --------------------------------------------------------

From: "dhsatyadhana" <dhsatyadhana@...>
To: <ultralightdx@...>
Sent: 29 October 2011 18:47
Subject: [ultralightdx] Re: Working with shorter (and cheaper) ferrites - The Backpack FSL

Hi Micheal:

I forgot to mention, in response to your other question: Steve R.'s experiments showed that ferrite
length doesn't add sensitivity, but only adds to the inductance. So, wrapping a couple more turns
around shorter ferrites would give the same inductance, and at least equal performance. As long as
you don't run out of space to wind the coil, the shorter ferrites appear to provide the same result.
This matched what Graham reported in his theory discussion.


--- In ultralightdx@..., "Michael" <michael.setaazul@...> wrote:

Expanding on this idea, has anyone tried using a row of
25mm or larger dia RF ferrite cores simulating a
thick hollow ferrite rod in a budget FSL?

Are diameter and length or is the mass of ferrite inside
the coil more determinant?

A smaller coil diameter might be in part offset by greater
length if more cores were used, pressed firmly together,
and/or by using a trangular array of three rows of cores,
thereby increasing the mass of ferrite.

Pre-empting experimental results, what performance
might theory suggest?

Ferrite cores are, I know not why, more affordable than
a recommended number of rods or bars. However, the
cost-performance ratio might not be better.

Michael UK

----- Original Message ------------------------------------------------------------------------

From:Kevin S
Subject: Working with shorter (and cheaper) ferrites - The Backpack FSL

I've been swamped at work lately, but have managed to do some experimenting with Ferrite Sleeve
(FSL) antennas using shorter ferrites, seeing if smaller and cheaper FSLs are possible. Graham's
initial FSL article indicated that ferrite length in itself is not a critical parameter: it is the
coil of wire that receives the signal, not the ferrite. As long as there is sufficient ferrite in
the vicinity of the coil, providing the "FSL effect" if you will, the signal developed in the coil
should be the same. Some of Steve R.'s experiments earlier this year seemed to confirm this.

To test this, I recently built what I call the Backpack FSL, a summary of which is now posted here
in the Files Section, in the "Ferrite Sleeve Loop Antenna" folder (bottom of the main Files page).
This design uses 65 mm (about 2.5 inch) ex-Soviet NOS ferrite rods, which are of the same #400
ferrite material as most other ex-Soviet ferrite. I have also started to rough out a large FSL
using the 62 mm Soviet bars, sold by at least a couple eBay sellers, which run about three for a
dollar depending on the quantity.

Join to automatically receive all group messages.