Hello and welcome to Pascal F5PNP!
I am sure that we were interested to learn of your plans for 136
kHz.
During the design of the little 'Marathon' QRP TX, I did try to
avoid the use of special ring cores like the 3c85 (or the
alternative 3c90 material), but nothing worked as well! You
could try using ring cores intended for EMC filters (often
coloured yellow/white), but they will be more lossy.
To Everyone:
Many LFers in Europe and elsewhere have found local companies
that sell 3c85/3c90 ring cores, and I would be happy to update my
web-site with details of companies that sell these ring cores in
small quantities: Please Email me direct with the details!
(Pascal, I would be pleased to buy some 3c85 cores and send them
to you - please Email me direct with your address.)
I think that building a converter for 136 kHz is a good idea. It
will work well with the 40 m dipole - but you will need to
resonate the antenna using a loading coil. And the converter
will need a good bandpass filter before the receive RF stage or
mixer. At GW4ALG, I use only small antennas on LF, but I have
never needed a pre-amp - the gain in my mixer is enough. The
circuit of the receive converter section of my 136 kHz
transverter can be seen at:
http://www.alg.demon.co.uk/radio/136/transvtr.htm
To find out more about building variometers, see:
http://www.alg.demon.co.uk/radio/136/ldg_coil.htm
.... In a variometer, the coil inside is put in
serie between the two outer coil of the variometer; or we build first the
outer coil, and then, we connect the inside coil in serie to terminal...???
My preferred wiring configuration for variometers is shown at:
http://www.alg.demon.co.uk/radio/136/ldg_coil.htm#mark2
You can build the outer and inner coils separately, and join the
coils together later using soldered connections or 'chocolate
block' terminal strip.
It would be much more fun to experiment on 136 kHz (especially
when running QRP) if you had some local OMs also wishing to
explore LF. Discovery is much more exciting if it happens as
part of a group activity - with everyone sharing ideas, and
learning from each other! Perhaps this would make a good club
project at F6KAW?
Other active stations on 136 kHz are F6CNI and F6BWO.
Good luck on 136!
Regards to all,
Steve GW4ALG
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