The antenna is the most important part of any system. It does not matter if you have a $11,000 radio if the antenna bad then you will not get the best for your radio and of course if you are limited on space this can make a difference as well. Remember this as well the band you want to work will make the difference on the size of the antenna you want to build as the lower the band you use the antenna you want to build will be larger due to the wave length. Even if you want an antenna at half wave length on 40 meters (7mhz) you will still need an antenna at 20 Meters (787 inches) of course you can build at ¼ wave i.e. 10 meters (33 feet).
All lot of new Hams get into the hobby via the technicians Class Ham License and most buy 2 Meters Radio(1444mhz to 148mhz). Now with this band you can build a ¼ wave antenna at 19 inches.
You will see a lot of this Symbol λ when working with Antenna’s this is this symbol for a full wave length so when you see ½ λ You know it means half wavelength ¼ λ quarter wavelength and so on.
Here is an Antenna that is easy to build and gives you a good performance due to its low angle of radiation. I will cover radiation at a later time but not to send you to sleep.The Antenna is called a J pole. It was designed by the Germans back in the days of Zeppelin air ships. Here is a run down of the J pole antenna.
The J-pole antenna, also called the Zepp' antenna (short for Zeppelin), was first invented by the Germans for use in their lighter-than-air balloons. Trailed behind the airship, it consisted of a single element, one half wavelength long. This was later modified into the J-pole configuration, which became popular with amateur radio operators, as it is effective and relatively simple to build.
The J-pole antenna is an end-fed omnidirectional dipole antenna that is matched to the feedline by a quarter wave transmission line stub. Matching to the feed-line is achieved by sliding the connection of the feedline back and forth along the stub until a VSWR as close as possible to 1:1 is obtained. Since this is a half-wave antenna, it will exhibit gain over a quarter-wave ground-plane antenna. The J-pole is somewhat sensitive to surrounding metal objects, and should have at least a quarter wavelength of free space around it.
A well known variation of the J-pole is the Slim Jim antenna, which is related to the J-pole the way a folded dipole is related to a dipole. Invented by Fred Judd (G2BCX), the name was derived from its slim construction and the J type matching stub (J Integrated Matching).
Both antennas should ideally be fed with balanced line, however a coax feed line may be used if a balun is added. Commonly, a choke balun is used, or an air transformer, using about five turns of coax. Typical construction materials include copper pipe, ladder line, or twin-lead. Coax can be used to match the J-pole as somewhere between the closed circuit and open circuit of the stub an exact 50 ohm impedance match exists.
The parts list is as follows.
1 10ft 1/2 copper water pipe.
1 1/2 copper elbow
1 1/2 copper tee
2 1/2 copper caps
1 5 pack 1/2 2-hole pipe strap
1 1 foot of 14 awg wire(i could not get bare wire so had to strip the shielding)
1 so-239 Chassis Mount Female Solder
2 packets or 1 packet if they come with 4 but you will need four in total of 6-32 x 1- 1/2 machine brass screws
1 packet 6-32 hex brass nuts
1 packet of brass washer washers
1 roll of solder
1 tin of flux(You can get all the Plumbing stuff from Lowe's)
one propane blow touch
This was the end result when i put the antenna together..
Once you move the 2 clamps up and down until your SWR is good then you can solder the clamps in place to keep the antenna Tuned.
I have also had some luck on 70cms but the SWR goes as low as 1:5:1 but on 2 meters the SWR is at a good 1:2:1.
This video on you tube helped me i hope it helps you.
Good luck on building the antenna.
http://www.youtube.com/watch?v=QOwznvSA-sM
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