Now, given that a "transmission line transformer," as distinct from a
conventional transformer built using transmission lines, does not
support flux in the ferrite; how is it that the ferrite makes the line
appear longer?


The ferrite makes the line look longer by way of it's permeability, but
that's obvious and I think I'm not understanding your question correctly.
Dye and Granberg cover that in their Motorola application notes as well as
in the section on TLTs in their book "Radio Frequency Transistors:
Principles and Practical Applications." They briefly mention in the book
that the coupling takes place in the magnetic material only at low
frequencies. This effectively makes the line(s)look longer as you are no
longer functioning as a TLT but instead as a flux-coupled transformer, and
the line length is now a function of the physical length of the conductors
and the permeability of the material. In practice a thumbnail approximation
is generally:

L' = L x sqrt(u)


Second, if this were to occur (through the design of a "transmission
line transformer" that was a voltage BalUn); what is the advantage of
longer lines?


It's a matter of what's practical. If you were to use very short lines
along with a high permeability material such as Fair-Rite 73, you may
encouter a region where the lines are too short to couple properly and the
magnetic material is well above the ferroresonance frequency. And even when
you do get into the flux-coupling môde, you still need to have sufficient
line in order to obtain decent coupling at lower frequencies. So, you have
to balance the two (line length and magnetic material) in order to obtain a
wideband transformer that has consistent performance over the desired
frequency range.

I hope I've covered everything here adequately.

Chris

,----------------------. High Performance Mixers and
/ What's all this \ Amplifiers for RF Communications
/ extinct stuff, anyhow? /
\ _______,--------------' Chris Trask / N7ZWY
_ |/ Principal Engineer
oo\ Sonoran Radio Research
(__)\ _ P.O. Box 25240
\ \ .' `. Tempe, Arizona 85285-5240
\ \ / \
\ '" \ IEEE Senior Member #40274515
. ( ) \
'-| )__| :. \ Email:
| | | | \ '. http://www.home.earthlink.net/~christrask
c__; c__; '-..'.__

Graphics by Loek Frederiks

"Richard Clark" wrote in message
news
On Mon, 27 Jun 2005 05:01:07 GMT, "Chris Trask"
wrote:

He also fails completely in understanding that
the ferrite used in transmission line transformers is to improve the low
frequency end by making the transmission line appear longer.

Hi Chris,

Now, given that a "transmission line transformer," as distinct from a
conventional transformer built using transmission lines, does not
support flux in the ferrite; how is it that the ferrite makes the line
appear longer?

Second, if this were to occur (through the design of a "transmission
line transformer" that was a voltage BalUn); what is the advantage of
longer lines?

73's
Richard Clark, KB7QHC