Date: Sun, 14 Apr 2019 12:21:28 +0100
From: Chris Wilson <dead.fets@gmail.com>
Message-ID: <128073171.20190414122128@gmail.com>
To: rsgb_lf_group@blacksheep.org
MIME-Version: 1.0
Subject: LF: Matching transformer for LF and MF question, ferrite material?
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


Hello  LF'ers

I  am having a play listening on LF. I have found the variometer alone
in   my  loading  coil  will  resonate  my  strapped  vertical  feeder
horizontal  quad  loop antenna, I do not need the main loading coil. I
have  a  question  re  the impedance matching transformer though. It's
based  on  a W1VD design, an excerpt from Jay's web site describing it
is pasted here:


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The gray box at the lower right houses the transformer which matches
the antenna resistance to 50 ohms. The transformer has a tapped
primary and secondary. The two rotary switches select 12 different tap
combinations that provide a matching range from 12.5 - 35 ohms up to
the 50 ohm transmission line impedance.

The transformer is wound on a stack of three FT-240-77 cores. Each
core is individually wrapped with Scotch 27 glass electrical tape. All
three are then wrapped into a single three core assembly. #14 solid
THHN is used for the primary (14 turn) and secondary (10 turn)
windings. It's important to wind the primary and secondary so that the
turns are interleaved and not wound so that they are on opposite sides
of the core. The primary is tapped at 12 and 13 turns and the
secondary at 7, 8 and 9 turns. Wiring between the switch terminals and
the transformer and connectors is made with flexible #14 stranded
THHN. Eye terminals are used throughout the transformer box, loading
coil and variometer to allow for quick disassembly and repair,
replacement or modifications to the system. All eye terminals are
soldered rather than crimped and brass machine screws and nuts are
used at all connection points.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Will I be OK still using the FT-240-77 cores at MF, both for RX and if
I manage to get my full licence or a friend with one operates here for
TX?  Or  do  I  need to build another with different cores? What type?
Thanks.


-- 
Best regards,
 Chris                          mailto:dead.fets@gmail.com