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Old Dec 16, 2009, 10:07 PM
IBCrazy is offline
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Amherst, VA
Joined Jun 2006
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The good ol' half wave dipole

Half wave dipole antenna:

This is by far the most commonly referenced real antenna. It has excellent efficiency and has a simple doughnut shaped radiation pattern. The gain of this is approximately 2.15 dbi. So it has fairly wide coverage. This is best suited for long range and altitudes. For range and general flying, it should be mounted vertically. However for high altitudes directly above your ground station, this is often better mounted horizontally. Change the antenna to suit your flying.

Coaxial fed dipole

This is the easiest to make and the one which I get the best results. You need RG-174 50 ohm coaxial cable and an SMA fitting for RG-174. You can also use RG316, which is more tolerant of heat.

Strip 3/4" of the jacket off of one end of the coaxial cable. Then strip 1/4" from the center element in the cable. Solder the center element to the pin. Then insert the cable with the pin and fold the shielding over the outer end of the SMA plug. Solder the shield to the outer part of the plug. (Note: you can also buy an extension cable and cut it instead of doing this step)

On the other end of the cable, strip 1/2" off of the cable and then strip 1/4" off of the center conductor. Pull the shielding around the center conductor and bend the center conductor 90 degrees. Now solder these to a proto board (you can get proto boards at Radio shack) so they run in opposite directions. Now solder on your elements (I used 12 AWG solid wire). One element is connected to the shield, the other is connected to the center conductor. On principal, the white is element is always connected to the center conductor and the black is always connected to tht shield. Each leg should be exactly your 1/4 wave measurement from the center of the antenna. The antenna should therefore be 1/2 wave

If you plan to optimize your antenna, you can leave the elements an inch longer or so and trim using the RSSI method described later.

Direct connected dipole

The half wave dipole is constructed from two separate quarter wave antennas oriented 180 degrees apart. The angle doesn’t need to be perfect. So don’t worry too much about it.

To build this I’m using 22 AWG solid wire, an SMA plug, and a ball point pen. The insulation on the wire doesn’t matter. This wire is available online or at your local Radio Shack store. The SMA plug is also available at radio shack or www.dpcav.com . You can use an antenna tube or any narrow diameter plastic tube as a substitute. Eve a coffee stir works. DO NOT USE CARBON FIBER!

Cut off 2 pieces of wire about 2” longer than your calculated quarter length (you will trim this later). Solder one wire to the needle of the SMA plug, solder the other to the outside of the SMA plug. Wrap the wire just above the needle in electrical tape until the wrapped diameter fits tightly into the SMA plug. Insert the needle into the plug until the entire narrow portion protrudes from the base. Bend each wire 90 degrees so they are flat and in line with one another. Cut each wire to exactly the quarter wave measurement from the bend. If you plan on tuning this antenna as described later, cut it to to ” longer than that measurement.

Remove the ink cartage from your ball point pen and evacuate the ink. Melt or slice a small section about ” long down from one end. Now slide the tube over the active antenna wire (the one connected to the needle) until the wire is completely encapsulated. The wire should protrude out of the bottom of the tub where it goes into the SMA plug. Slide another tube over the other end of the antenna and then secure them in a straight line.

You may also build this antenna on a circuit board and feed it directly with coaxial cable. In this case simply strip the coaxial cable and feed one end to each wire. The wires should be less than ” apart and the same lengths as your quarter wave calculation. Slide your tube over each end and secure.

EDIT: Alternately, you could build Mr RC Cam's dipole using a length of coaxial cable and stripping it back. It is truly an excellent design. Total length would be exactly twice your quarter wave length.
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Last edited by IBCrazy; Jan 11, 2011 at 10:06 AM. Reason: Added more photos
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