Building Your Own FM antenna!
Make your own antenna for FM DXing (88-108mhz)
This is a classic ten element design. I bought this antenna around 1970 and just retired it this spring. This is a Finco design. Maximum gain of this antenna was in the 9-10db range. Directivity is good and front to back ratio is alright, but not quite as good as the APS-13 or the Channel Master Stereo Probe 9. Here are the specs, in case you want to experiment with the design:
Boom Length: 120 inches (302cm)
Reflector Length: 70 inches (178cm)
Dipole D1 Length: 60 inches (152cm)
Dipole D2 Length: 46 inches (117cm)
Director A: 47 inches (120cm)
Director B: 47 inches
Director C: 49 inches (124cm)
Director D: 49 inches
Director E: 51 inches (130cm)
Director F: 51 inches
Director G: 51inches
Next, here is the spacing between elements:
Length AB: 12 inches (30.3cm)
Length BC: 12 inches
Length CD: 12 inches
Length DE: 12 inches
Length EF: 12 inches
Length FG: 12 inches
Length G to D2: 12 inches
Length D2 to D1: 17 inches (43.2cm)
Length D1 to R: 16 inches (40.6cm)
Dipole D1 has a shorting bar 10 inches (25.4cm) away from the boom on either side. Dipole D2 has a shorting bar 12 inches (30.3 cm) away from the boom on either side. The shorting bar is nothing more than a thin piece of aluminum which connects the upper and lower sections of the dipole on both sides of the dipole.
Antenna connections. Dipoles D1 and D2 are connected as shown in the diagram. Looking at the diagram, the antenna connections are made at a point 5 inches (13cm)to the left of dipole D1, after which the wires cross and attach to dipole D2 on the opposite sides. These two wires should NOT touch.
Finco also made a 6 element version of this antenna. Maximum gain was about 3 db less than the ten element design. Try building this antenna minus directors A,B,C, and D.
Hints on building an antenna. The easiest way to find aluminum for the elements, etc is from old antennas you may find. Look for neighbors hooking up to cable and throwing away their TV antennas. Look for damaged antennas with one or two bent elements waiting for the trash collectors to haul them away. If making a closed loop dipole is too difficult, make an open dipole (as Radio Shack does in their FM antennas). To connect the dipoles together, use solid guy wire from a hardware store. This wire is about the right size. Find a plactic rectangular block about 2 inches (5cm) long, and drill two holes about 1.5 inches (3.7cm) apart. Get two long screws, some washers, and connect the two wires to the plastic block. Add two more washers per side, another nut (or wingnut) on either side, and you have made it possible to attach your lead-in to your antenna.
If you are low on cash but have access to some old TV antennas, trying making your own design using this design as an aid.
Note: This antenna has been out of production for years and the company that manufactured it is no longer in business.
