Thanks for the clarification, Gary. It is curious that there can
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be such a difference with different foam. Material composition
may be significant, but is thickness and spacing more critical
than quality or composition of the foam?
Has anyone in the Old World experimented with locally
available materials - including hoarded packaging stuff?
With the rods recovered from old hotel radios, I might give
it a try. However without comparison with an optimised design,
I would never know how well my knock-up was performing :-)
On 07.03.16 02:35, D1028Gary@aol.com [ultralightdx] wrote:
. . .
The choice and thickness of the foam between an FSL's coil and its
ferrite material is a major factor in determining an FSL's ultimate
sensitivity. The 1/4" (6mm) thick Oatey foam is strong and resilient,
and has provided excellent results in FSL antennas since 2011. Along
with substitutions in the type of Litz wire and ferrite material,
substitutions in the type of foam are not recommended if someone wishes
to obtain the designed MW sensitivity in a hard-wired FSL Tecsun PL-380
After the U.K.'s Graham Maynard published his original Ferrite Sleeve
article in 2011 there was a torrent of experimentation here in the U.S.
to determine the best possible components for maximum FSL sensitivity.
Ferrite bars, ferrite rods, Litz wire, foam material, frame material and
variable caps were all thoroughly investigated. Various brands of foam
material were tested in various thicknesses, and the original FSL
experimenters (Steve, Kevin and I) determined that a thickness of about
1/4" (6mm) was close to ideal for maximum sensitivity.
. . .