A better improvement than this awaits your radio
reception...Improving the reception of an FM radio can be done by
you at home, simply by replacing the antenna with a 5/8 wave
folded dipole antenna. Many radios and most home stereo receivers
include antenna terminals for the connection of an external
antenna. Usually the supplied antenna is a minimalist design
(often an "internal" type, such as a telescopic rod or a short
length of wire). This can be greatly improved for very little
money outlay. All of the items needed are available from a local
electronics store or hardware stores.
!! Steps !!
* Which is the station you want most?Determine the frequency of
the station desired to be tuned. The antenna is tuned to a certain
length, based on the frequency of the connected radio. Regardless
of the particular frequency, the entire FM broadcast band (88 -
108 Mhz) of the radio's tuner will receive stronger signals from
the antenna, with the largest increase seen at the frequency
selected in this step, and slightly less as the radio is tuned
away from the design frequency.
Calculate the length of the antenna. The formula for a 5/8 wave
antenna using typical 300 ohm "twin lead" is L = 300/f x 5/8 x 1/2;
where "L" is the length in meters of the antenna and "f" is the
frequency in Mhz of the station to be tuned. This can be simplified
to L = 93.75/f.
* An antenna built for 98 Mhz would be: 0.9566 meters or 95.66 cm
(centimeters) long. For those more familiar with imperial units
than metric, the formula to convert centimeters to inches is: cm X
0.3937. This means 95.66cm X 0.3937 = 37.66 inches long.
Improve the antenna design. The antenna improvement in this article
is a design for a simple 5/8 wave "folded dipole" or "T" shaped
antenna. This design will outperform any internal or telescopic rod
antenna that may have been supplied with the receiver. It is also
similar to those provided with some more expensive stereo receivers.
* To improve upon this design, simply double, triple, quadruple,
etc. this value as such: 37.66" x 2 = 75.32", or 37.66" x 3 =
112.98", and so forth.
* The 112.98 inch antenna will outperform the 75.32 inch antenna,
which outperforms the 37.66 inch antenna.
* Of course, there is a "point of no return" when the multiple is so
great that the signal at the ends of the antenna cannot travel the
entire length due to the electrical resistance of the wire. This
limit is around 100 meters (a little more than the length of a
football field).
"600 Ohm Ladder Line" and 450 Ohm line are physically larger
than 300 Ohm Twin Lead and is rated at 600 and 450 ohms
respectively; as opposed to 300 ohms for twin lead. These
cables can be used, but require the use of a different formula
to design. Standard 300 Ohm twin lead cable was selected
because it enjoys wide availability. Cut the feed line. As
described above, this antenna looks like a "T". Thus far, the
calculation has been for the top horizontal part (top of the T)
of the antenna. A vertical (bottom of the T) needs to be
connected to the top horizontal to facilitate connection of the
antenna to the receiver's antenna terminals. While both the
horizontal and vertical parts function as an antenna, the
vertical portion is referred to as the feed line.
* Cut a length of twin lead that is equal to or a multiple of the
length calculated above. That will be long enough to extend
between the receiver's antenna terminals and the horizontal
portion when installed.
Prepare the antenna for connection to the feed line. Locate and
mark the halfway point on the length of the horizontal portion of
the antenna.
* Use a razor knife to cut a 1 inch (2.5cm) long slit (centered on
the halfway mark), parallel to and between the two wires in the
antenna's twin lead cable.
* Cut through one of the twin lead wires at the half way mark.
* Strip the insulation from the cut ends of the wire at the halfway
point and the ends of the entire horizontal length (this should be
about a 1/2 inch (1.27cm) from each side).
* Prepare the feed line for connection to the antenna. Use a razor
knife to cut a slit between the wires of the twin lead about an
inch (2.5cm) in length at both ends. Carefully remove a half inch
(1.27cm) of insulation from each of the wires on both ends.
Strands of the feed line wires prior to twisting and
soldering.Tin the exposed twin lead wires with solder. Re-twist
the individual strands of all wires to keep them tightly
grouped together. If soldering is not an option, skip to the
next step after stripping insulation from the wires indicated
at the end of this step.
* Apply a small amount of electrical grade soldering flux (do not
use plumber's flux as it contains acid). A small 20 to 50 watt
soldering gun or iron to heat the wires is sufficient.
* Shortly after the flux melts, apply electrical grade solder to the
wire near the soldering gun's / iron's tip (use of straight solder
or flux core solder is fine - but do not use acid core solder).
* Apply just enough solder to the heated wire so that melted solder
flows back into the insulation, then remove the solder and heat
from the wire. Do this for both wires at (1) both ends of the feed
line, (2) both wires at both ends of the horizontal antenna piece
and (3) both wires at the cut made at the center of the horizontal
antenna piece.
Solder the antenna and feed line together. Solder the two wires at
one end of the horizontal piece together and repeat for the other
end (if not soldering, create a solid electro-mechanical connection
by tightly twisting the wires together instead of soldering).
* Lay an end of the feed line at the center of the horizontal
antenna piece so that the soldered leads of are close to each
other. The left wire of the feed line should be soldered to the
left wire of the antenna, and the right wire of the feed line
should be soldered to the right wire of the antenna.
* When completed correctly, a path can be traced that starts on one
wire in the feed line that continues to one wire in the bottom of
the antenna and continues to one end of the antenna. It continues
across the top wire of the antenna to the opposite end. It begins
the return on the other bottom wire of the antenna to the other
wire in the feed line and finally terminates at the end of the
feed line.
!! Tips !!
* Typical 300/75 Ohm Balun with twin lead cable connected to the
screw terminals. The 75 ohm connection is simply pushed on the
threaded connector. A "300 to 75" ohm balun will be needed if the
receiver offers only a 75 ohm (coaxial cable)antenna connection.
These are devices that allow for the connection of 300 ohm twin
lead that converts to and provides a screw-on 75 ohm connector.
!! Warnings !!
* Antennas that are placed outside should have lightening protection
on the feed line.
!! Things You\'ll Need !!
* 300 ohm twin lead antenna wire
* 20 - 50 watt soldering iron / gun
* Solder w/ rosin flux core (not plumber's solder)
* Flux (not plumber's flux) (if not integral to solder wire)
* 300 / 75 Ohm balun (if needed)
* Wire stripper
* Wire cutter
!! Article Tools !!
* Read on wikiHow
*
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