Date: Sun, 28 May 2000 00:11:24 -0700
From: "John, KI6WX" <ki6wx at pacbell.net>
Subject: [Elecraft] Different Construction Method for T2

There has been some discussion on this mailing list of how to wind T2.  My
original version of T2 would only give 4.9 watts out on 10 meters; after
rewinding it twice, I got that up to 10.4 watts (all measurements using
Elecraft built-in wattmeter).  But I still had concerns that T2 was not as
optimized as it could be.  I made a series of measurements of the input and
output voltages of T2 using a Tek475 scope; ideally, one should see 1/3 of
the voltage at pin 3 or pin 4 compared to the input at pin 1.  This ratio
held true for the lower bands (within measurement error), but was definitely
lower on 10 and 12 meters.  On 10 meters, one would only see 72% of the
expected voltage which indicates that not all of the flux being generated by
the primary winding is coupling into the secondary.

To fix this problem, I tried winding T2 on a different core.  I used an
Amidon BN43-302 binocular core (a smaller version of the core used in T4).
This core should give better coupling at higher frequencies.  The core was
wound with the same 24 guage hookup wire used to wind T4.  The primary has 3
turns and the secondary has 2 turns (the wire must pass through both holes
in the binocular core to create one turn).  The primary comes out one end of
the core and secondary out the other - see the directions on winding T4 if
you need clarification.  This version of T2 is mounted about 1/4" above the
PC board so the core can clear capacitors C129 and C130; the primary
windings connect to pins 1 and 2, and the secondary winding to pins 3 and 4.
The mounting makes it look exactly like a smaller version of T4 with T3 in
between them.  The hookup wire holds the core in place with less free play
than T3.

After replacing the core, my output power on 10 meters increased from 10.4
watts to 12.0 watts.  The scope measurement showed that 87% of the expected
voltage was now appearing on pins 3 and 4.  There were no other significant
changes observed.  I have several extra cores if anyone else wants to try
this experiment or you can order them direct from Amidon.

- -John
 KI6WX