Page 37 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits
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FIGURE 3-1 Ferrite-bar/rod antenna coils.
Ferrite antenna coils are readily available on the Web such as oneBay. An
alternative to making an antenna coil is to buy ferrite rods or bars and wind your
own coil. The ferrite material should be at least 2 inches long and a paper insert of
l
about 1.5 inches should be wrapped around the ferrite material such that the insert
can slide. The magnet wire of about 30 American Wire Gauge (AWG) or No. 40 Litz
wire is wound in a single layer over about 1.3 inches of the paper insert. With an
inductance meter, measure the inductance when the insert is in the middle of the
ferrite material and when it is toward the end of the ferrite material. If there is too
much inductance, unwind some of the wire while measuring the inductance. If
there is not enough inductance, splice the wire by soldering and wind in the same
direction as the first single layer.
In most high-fidelity home stereo receivers today, the AM radio antenna is just an
air dielectric loop (Figure 3-2).
