Making your dipole antenna yourself is always better than buying one .
What do you need: cu wire , balun 1:1 and rope . For the wire I use : CQ-532 antenna wire (AWG 18) , is a little more expensive but is UV resistant and light weight .
The most widely used formula to calculate the approximate overall length of wire required for a
dipole is : 468 / frequency (MHz) = length of wire in feet or dipole length in meters :
143 / frequency in MHz .
Dipoles have a feed point of about 75 Ohm in free space and can be fed with a 50 Ohm to 75 Ohm coax with or without a 1:1 balun .
The use of a balun is highly recommended . By isolating the feedline, you won't get RF in the shack, and your dipole will behave like a real dipole . Your coax line will be a coax line , not a part of your antenna .
The length of wire required for a given frequency is found with the help of an antenna calculator . however, the actual resulting frequency of resonance and feed-point impedance of a dipole will depend on :
When each side of a dipole slopes down from the feed point , it is commonly called an inverted V and the results are different from a normal dipole .
To avoid cutting the wire , I usually just fold back each end of the antenna wire on itself and tape it tight if it's insulated wire - or twist it back on itself if you are using bare wire . The resonance frequency shifts upwards . After you can go easly back to the beginning of the band and vice versa . Especially on the lower HF bands recommended , because the bandwidth is not wide (100-150 Khz) . And for a temporary setup a must .
Therefore, the angle between the two legs of an inverted V should not be less than 90 degrees .
A lot of articles have been written about the meaning and the unintentional use of a
balun with a dipole antenna . My experience is: use a current balun.
Making a balun yourself is not difficult. The construction and choice of materials are important, especially when using high power . On the picture you can see 2x4 turns , I using 2x6 turns .
1: Ferrit Toroidring for instance FT240-61 or FT240- 43 or for lower bands FT240-31 .
2: 1 Meter Teflon coax cable like RG 142 or Rg 303 up to 2KW .
3: Waterproof plastic box .
4: PL SO239 socket .
5: M6 inox bolts and screws .
6: rubber sealing washers .
If the antenna has no connection to ground , add a small 10 K resistor between center conductor and braid of the coax to discharge static electricity .This prevents "noisy tick" from statics .