----- Original Message -----
Sent: Wednesday, May 18, 2005 3:43
PM
Subject: LF: cores
Hi All
Another anomaly about these ferrite transformers.
I wound a 3c type core with a Sec of 24 turns and measured it to be
1.38 mh then over wound this with the prim of 8 turns, this reduced the Sec to
982 uh with a prim of 110 uh. The ratio is about right x9 for a 1:3 ratio. I
suppose meaurements should only be made when the transformer is complete with
all windings, but it does show the effects of multiple windings over a single
layer.
Except one has a lot of test equipment it seems
most dabblers are working in the dark especially at LF, no wonder there are so
many BANGS especially the FETS!!!!!!!1
To guarantee a robust no bang amplifier maybe
TUBES are still the best bet.
From messages received it appears to be that as
long as the ratio Prim /Sec is correct the ferrite material is not important
but then why such a variety of different core material, although I do realise
that certain other ccts at HF work better with a particular core
mix.
I could do with some design literature written by
others that have experience in the ferrite transformer research
field.
73 de Mal/G3KEV
Hi Mal!
You do not tell how you measure
inductance.
First, you can be absolutely sure that in a
reasonably well designed transformer
(negligible leakage) the inductance ratio will
always be equal to the square of the
turns ratio.
When it comes to measuring inductance, things are
quite complicated. The
core permeability
is not constant with frequency, but varies quite a bit. In
ferrite
catalogues you will find a term called the
complex permeability. The real
component of this term is what gives you
inductance whereas the complex
component represents losses. Thus the inductance
reading you find is dependent
e.g. on the test frequency of your
inductance meter. In particular, if your test
frequency is high, you are really bad off!
With a high test frequency, winding
capacitances may come into the picture,
too.
A tip: Measure inductance with a test bridge at a
low (much lower than 136 kHz)
frequency and make
allowance for the complex permeability, -- or make your
measurement at 136
kHz (test set up: generator - inductance - variable resistor,
meter and a 3-dB
criterion).
73=
Niels/OZ8NJ+
