Hi Group,
As I am planning to use an audio amplifier as a PA
on 136 kHz, I need to
transform the amplifier output (100 Watt at 4-8
Ohm) to 50 Ohm to match
it to the coax cable to the antenna, possibly
with a 50 Ohm low-pass
filter in between. Not much information is
available on the Internet
about such a specific configuration. I am
fond of capacitor impedance
transformation, which I use with success
for matching and tuning my loop
antenna on 475 kHz. Could I employ the
same concept to step up impedance
from 4 Ohm to 50 Ohm at the output of
my audio amplifier?
I have also looked into using ferrite toroids
as transformers but the
sheer amount of information on this subject,
often incomplete and
contradictory, is confusing me. It looks like many
are using "3C90" as a
core material, but this type of core seems
difficult to acquire - at
least for me here in Norway. I understand
that "type 77" material could
also be used and this one is easier to
get by. If I would opt for an
FT140-77 core, would this be suitable as
a transformer toroid for 100
Watt on 136 kHz or would I need a bigger
one? And how many primary and
secondary turns would such a tranformer
need to step up from 4-8 Ohm to
50 Ohm?
I would be very grateful
for some input on this subject before I start
ordering (the wrong)
components.
73 de Robert,
LA4ANA
