From: "Marcin" <bxi@go2.pl>
To: <rsgb_lf_group@blacksheep.org>
References: <128073171.20190414122128@gmail.com>
In-Reply-To: <128073171.20190414122128@gmail.com>
Date: Sun, 14 Apr 2019 15:00:41 +0200
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Subject: LF: RE: Matching transformer for LF and MF question, ferrite material?
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Hello Chris,
My universal antenna autotransformer for 8.27kHz, 136kHz and 472kHz:

https://klubnl.pl/wpr/en/index.php/artykuly/uniwersalny-nadawczy-autotransfo
rmator-antenowy-na-pasma-827khz-136khz-i-472khz/

73! Marcin SQ2BXI

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
<owner-rsgb_lf_group@blacksheep.org> On Behalf Of Chris Wilson
Sent: Sunday, April 14, 2019 1:21 PM
To: rsgb_lf_group@blacksheep.org
Subject: LF: Matching transformer for LF and MF question, ferrite material?


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