RHF wrote:
BPNJ,

When back and checked the eBay Auction Listing.

The main Photo/Image shows Two (2) 'separate' "Individual" Ferrite
Rod Loop Antenna Heads (VLF & AM/MW) with one Base Unit.

AFAIK - The Coil is the Coil and for the same 'type' Ferrite Material
and Cross Sectional Area: The Coil will not vary too much in its size
and length for the same band of frequencies.
? Comments Please . . .

Think about that in terms of the size of coil in a GE Superadio and a
small pocket radio. They cover the same frequencies. They are a
different size. Size alone does not dictate inductance. For a given
capacitance, the inductance needs to stay the same if you are covering
the same frequencies.



Most Ferrite Rod Antenna Coils that I have seen for AM/MW are Single
(One) Layer Wrapped: Most likely because for the at home builder
'doing-it-by-hand' this is the easiest method.
? Comments Please . . .

Most antennas are mass produced so the home builder has little to do
with it. For the home builder the easiest thing to do is a jumbled mess
wrapped around the form.


However - I have seen Coils that a
- Evenly "Spaced" over the 'full length' of the Ferrite Rod
- Single Coil = One Coil near one end of the Ferrite Rod
- Twin Coils = One Coil near each end of the Ferrite Rod
? Comments Please . . .

The person designing the antenna has many choices that can be made.
Different spacing affects coupling and stray capacitance.


For the same 'type' Ferrite Material and Cross Sectional Area as the
Ferrite Rod gets Longer and Shorter the amount of RF EMF Energy
{Signal} gathering Increases or Decreases respectively.
? Comments Please . . .

If that were the case, then small portable radios would be deaf. Some
small radios are considered very sensitive.


The Ferrite Rod is used to gather and concentrate the RF EMF Energy
{Signal} and reduce the physical size of the Antenna Element for
an effective smaller antenna.
? Comments Please . . .

That is the effect of permeability of the material. (Hint: this is one
of the key magnetic properties that matter.)



It is my understanding that for a given 'type' Ferrite Material with
a given Cross Sectional Area the Ferrite Rod can only be so long
before the Gains are overcome by the minuses of using a longer
Ferrite Rod.

You are talking about design trade offs, but don't present anything
specific. An assumption is made that the length is a major driver in
performance. You don't indicate what 'minuses' you are referring to.

At some point as the Ferrite Rod gets longer; then
the Cross Sectional Area has to Increase too.

Why, what dictates that? Please present some information supports your
statement. This would indicate a magic point for length to area ratio.

The result is a
Longer and Thicker Ferrite Rod and these are Costly Items that
usually do not warrant the cost based on any potential or actual
improvement Signal Handling.
? Comments Please . . .


You seems to be trying to make a connection between the effectiveness of
a ferrite antenna and its size without any understanding of how they
actually work.

Why not spend some time using Google (or a library) and do some real
research into the topic and report your findings back to the group?
Those findings can be backed with references and proper technical
reasoning. This would be better than the usual misinformation generally
seen. By the way, I do not consider references to posts in Yahoo groups
as being credible.

craigm

iane ~ RHF
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