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

Kevin Schanilec

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 Loop
(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.

. . .

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