Rolling your own antenna isn't too difficult.  Here are some basic measurements that will get you on the air.

Dipoles are mostly used for HF work.  It is an antenna with 2 "legs."  One leg is the driven, or transmitting element.  This is connected directly to your coax center conductor.  The shield of the coax is connected to the other leg, called the counterpoise.  Both legs should be the same, resulting in a combined half-wavelength overall. 

The formula is 468 divided by frequency in Mhz.  You can make kHz into Mhz by moving your decimal 3 places to the left, such as 1900 kHz being actually 1.9 Mhz.  Here are measurements for the most popular bands:

Band    Frequency        Half-Wave total         Each side should be

160m    1900 kHz          246 feet 4 inches          123 feet 2 inches

80m     3750 kHz        124 feet 10 inches           63 feet 3 inches

40m        7100 kHz        65 feet 11 inches         32 feet 11 inches

20m        14200 kHz      32 feet 11 inches           16 feet 6 inches

10m         28700 kHz     16 feet 4 inches              8 feet 2 inches

In the examples above, cut a wire to the length for your half-wavelength.  Then cut in half to create two dipole elements.  You may want to add 6 inches, then trim to resonance.  It is a hell of a lot easier to snip some wire off than trying to solder new wire on.  Note the lower you go in frequency, the longer antenna you need.  So if you plan on transmitting on 10 meters (around 28 Mhz) your antenna will be much smaller than if you wanted to transmit on 160 meters (1.8 Mhz) so plan according to what you can fit into your yard.

If VHF/UHF is your bag, then you're in luck.  Antennas get way smaller.  Dipoles per se usually aren't used up there, but electrically they can be.  I've made some roll-up antennas that work ok in a pinch.  Usually for handie-talkies to increase range in fringe areas.  I've used these from hotels and campgrounds.  They do help out, especially when you're trying to transmit with limited power.

Verticals are derived from the dipole, since they are essentially a dipole standing on its end.  One "side" of the dipole would be three or four radials hanging 45 degrees under a vertical radiator.  My favorite homemade antenna is a PL-259 socket, with brazing rods to make up the radials and the center vertical radiator.  These can usually be hung in an attic and are great for weather radios and scanners as well, since most ham VHF/UHF antennas also work for these.  If they are out of the weather and out of sight, why pay 50+ bucks for a quarter-wave antenna when you can make it yourself in under an hour for 5 or 10 bucks? 

Some element lengths:

6m       52 Mhz        54 inches

2m     146 Mhz        19 inches

440     446 Mhz         6 inches

Mobiles are even easier, since all you need to do is keep the driven element separated from the car body.  The car body is used as the counterpoise - the non-driven half of a dipole.  Get your antenna mount and ground it to the chassis, and cut the element for your desired frequency.

Beam antennas are also easily made from PVC pipe or wood, and stiff wire.  Measurements vary depending on number of director elements.  You can make Yagis, Quads or Delta-Loop beams.  I made a 2-meter beam a few years ago and I had good luck with it.  Plans with all measurements and materials can be found in most books about ham antennas, I'd recommend those by the Amateur Radio Relay League.  I bought a new one recently at Ham-Com in Dallas, and Joe Walsh signed it for me.  That was cool.

Experiment freely - the object of the game is to get your Standing Wave Ratio as low as possible and keep your Effective Radiated Power high.  For you newbies, that means getting as much signal out of the coax and resonating into the antenna, while losing the least amount of power.

See you on the bands.

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