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I
have built this homebrew Antenna
Matching Unit in an IBM PS/1 computer chassis.
It is symmetrical designed so either connection can serve as input or
output. The design
is a simple variable lowpass T-filter with input and output inductances
that
can be changed in four steps. In
between there is a capacitor to ground that is continuously varible.
The capacitor is made of four
heatsinks that is mounted in pairs and two of the heatsinks moves when
turning the C
knob. There is 28 turns from end
to end and the maximum capacitance is approximately 300pF with the
heatsinks
choosen.
The Heatsink Capacitor This 2nd homebrew Antenna
Matching Unit is also a variable lowpass T-filter. It is more
versatile since the inductansce is continuously variable. I planned to
use heatsink capacitors in this design also, but I had a suitable
variable capacitor in the junk box.
L1 is made of 15m of 1.5mm² solid copper
wire, wound on a ceramic core, approximately 100 turns. It used to be a
high power wire wound potentiometer (250Ω 250W). The inductance is
approximately 40µH. The copper wire is fixed with epoxy.
L2 is made of 36 turns of 1.5mm² stranded copper wire, wound on a piece of plastic pipe with a diameter of 32mm. The inductance is approximately 20µH. Each section of C1 is 150pF variable and C2 is 100pF. S1 can add or remove L2 in parallel with one branch of L1, to reduce or increase the inductance. S2 can add or remove C1A and C2, to increase or reduce the capacitance. The wire wound 250Ω 250W potentiometer L2 wound on a 32mm plastic pipe ... ... and fixed on the bottom flange of the box |