Building a Matching Transformer for Shortwave Listener's Antenna
using a Binocular Ferrite Core from a TV type Matching Transformer.

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From: (John Doty)
Newsgroups: rec.radio.shortwave
Subject: Low Noise Antenna Connection
Date: 26 Nov 1993 16:55:24 GMT

"The transformer is built around a toroid extracted from a TV
"matching transformer". If you're a pack rat like me, you have
a few in your basement: you typically get one with every TV or
VCR (or you can buy one). Pop the plastic case off and snip the
wires from the toroid (it looks either like a tiny donut, or a
pair of tiny donuts stuck together). The transformer windings
should be made with thin wi I use #32 magnet wire.
* The primary is 30 turns while
* The secondary is 10 turns.
For a one-hole toroid, count each passage of the wire down
through the hole as one turn. For a two-holer, each turn is a
passage of the wire down through the right hole and up through
the left.?
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MY BINOCULAR FERRITE CORE MATCHING TRANSFORMER PROJECT:

Well I tried two different "Binocular" Ferrite Core to 'build'
a Shortwave Listeners Matching Transformer for a Low Noise Antenna.
I was using #30 Magnet Wire and these Ferrite Cores are very
small 'tiny': 5.0mm H x 6.6mm W x 3.6mm OD x 1.8mm ID

But the maximum number of turns that I could get "In" and "Out"
of the two small holes was 14 Turns.

So I had to settle for a Primary of 9 Turns with a Secondary of 3 Turns.

This would be equal to Primary of 18 Turns and a Secondary of
9 Turns using a standard One-Hole {Donut} Toroid Ferrite Core.

Has anyone built one of these with this few number of turns and:
If So ? How Does It Work ?

* * * * * Binocular Ferrite Core TIPS * * * *
Here are some things to be Mindful of and Consider during the
Matching Transformer Winding Process:

* For these 'tiny' Binocular Ferrite Cores; you will be using
the same small size AWG #30 Wire for both Windings. So in your
Stationary-End of the Primary Winding "Tie" an Overhand Knot to
Identify 'it' after you have completed all your Windings.

* After your first One and a Half Turns (1 1/2T) with the Wire
Ends coming out of the Core from Opposite Sides PULL on both
Wire Ends to Tighten the Wire Wraps (Loops)

* Each Full Turn after the first 1 ½ Turns: 2 1/2T, 3 1/2T,
4 1/2T, 5 1/2T, 6 1/2T, 7 1/2T, 8 1/2T, 9 1/2T, ETC; with the
Wire Ends coming out of the Core from Opposite Sides PULL on
both Wire Ends to Tighten the Wire Wraps (Loops)

* Wrap the Primary {Antenna}Turns First and Get-Them-Tight.

* Place a Pencil and paper next to where your are wrapping the
Wire through the Binocular Ferrite Core; and Mark Down Each Turn
as you wind it. I Prefer to start my 'count' When I start the
Return-Pass-Through of the Wire. [Starting from the Bottom the
Wire goes Up (Out) through One Hole and then the Wire goes Down
(Returns) through The Second Hole.]

* Start the Secondary Turns from the Opposite-End from the
Primary Turns. Wrap the Secondary {Coax Cable} Turns and
Get-Them-Tight.

* If the Primary and Secondary are going to share a Common
Ground then take one Primary Wire End and one Secondary Wire
End and Twist them together. [ Do Not Use the Primary Wire
with the Knot at it's End for one of the Ground Wires.]

You will now have a "T" Shape Matching Transformer Assembly.
At the 'center' of the "T" will be the Binocular Ferrite Core.
The Vertical Leg of the "T' will be the Two Twisted Ground Wires.
The Left-Arm of the "T" will be the Primary {Antenna} Wire with
the Knot at the End. The Right-Arm of the "T" will be the
Secondary {Coax Cable} Wire.

If you are making several of these TV Binocular Ferrite Core
Matching Transformers. Them you may wish to use some Model Paint
of Nail Polish to Mark the Leads for easy visual identification
of the Leads as you are working with them.
Red - Primary {Antenna} Wire.
Green - Secondary {Coax Cable} Wire
Black - Two Twisted {Ground} Wires
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Some Say: On A Clear Day You Can See Forever.
I BELIEVE: On A Clear Night . . .
You Can Hear Forever and Beyond - The Beyond !
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iane ~ RHF
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Check-Out the Shortwave Listeners (SWLs) Antenna eGroup on YAHOO !
http://groups.yahoo.com/group/Shortw...na/message/502
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