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Author Topic: Homebrewing a Johnson Matchbox  (Read 1998 times)
KL0PE
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Posts: 24




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« on: September 26, 2001, 10:56:38 AM »

I have an old issue of 73 magazine which describes how to homebrew a Johnson Matchbox balanced line tuner.  The instructions are actually quite simple, but the article is text only with no pictures and only a basic schemetic diagram, so it's actually a bit hard to follow all the particulars, especially when it comes to winding the main coil.

Does anybody know where I can find more information and perhaps some detailed drawings or photos of the interior of a Johnson Matchbox?
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WB6BYU
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Posts: 13353




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« Reply #1 on: September 27, 2001, 11:29:55 AM »

http://www.cebik.com/link.html

Depending on the bands (and impedances) you want to cover,
there is another design which is probably easier to build:
the coil is opened at the center and  a 500pf variable capacitor
is connected between the two ends.  The feedline is connected
to the other ends of the coil with a split stator from each end to
ground (perhaps 150 to 250pf, depending on coil size and band.)
The coax is link coupled to the center of the coil.  This is basically
a link coupled, balanced pi network tuner.

Might be a good use for some of those old plug-in link-coupled
coils!
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VK7HL
Member

Posts: 1




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« Reply #2 on: November 27, 2001, 04:10:54 AM »

Hi. there,
You can find all the pictures at www.cebik.com/link.html
Would love to build one myself but the split stators are not available in Tasmania Hi!
Good luck
73
Lionel
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WB6BYU
Member

Posts: 13353




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« Reply #3 on: November 27, 2001, 11:49:49 AM »

Lionel -

The capacitors are difficult to find here, also, but there are ways
you can make your own.  One approach I've seen is to use the
tuning capacitors from the WWII-era ARC-5 transmitters.
(Similar to a ZC-1?)  These are 208 pf high-voltage variables.
The article I saw removed the rotor from one and mounted the
stator plates upside down over another capacitor on insulating
spacers, giving two sets of stators on  a common rotor.  Two of
these were then ganged on a common shaft.

I also saw an article on a tuner where the variable capacitor was
formed by two horizontal plates with a thin piece of glass between
them: one plate was moved horizontally to vary the capacitance.
This approach could be extended to build dual-differential variable
capacitors using two plates side-by-side with a single plate
moving over the top of them, though this probably would not be a
very compact unit.

Nice place, Tassie. . .  I spent a week wandering the island in 1980
with an Argonaut in my backpack.

Cherrio!  - Dale WB6BYU, ex-VK2DJW/4/5/6/7
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