How long should a doublet be?
65-75′ (good for 40 meters through 10 meters, but not for 80). Notice that the precise length is not critical. Much more critical is getting the doublet as high as you possibly can.
How efficient is a doublet antenna?
An efficient doublet should be at least 1/4λ to 1/3λ at the lowest operating frequency. A 3/8λ version has an efficiency greater than 98% relative to a λ/2 dipole and can have SWR values that are reasonably easy to match.
How does a doublet work?
The doublet antenna is a form of dipole that uses a balanced feeder, often open wire feeder and an antenna tuning unit. As open wire feeder is able to operate with levels of standing waves and effectively becomes part of the antenna, it is able to operate over a wide band of frequencies.
How tall does a doublet antenna need to be?
Much more critical is getting the doublet as high as you possibly can. Although the antenna will work at low heights in the 20-25′ range, it does much better (especially on 80 and 40) when it is higher than 35′ up.
Which is the best version of the doublet?
This version of the doublet tends to circularize the pattern, but reduce overall gain of the antenna at almost every frequency of use. Consider bending the elements instead (if supports are available).
What makes an all band doublet so good?
An all-band doublet is a rather refined antenna system when looked at in detail, but it is also relatively easy to get on the air with it. If the student runs into difficulties or has questions, the instructor can help him or her work out the answers.
What kind of transmission line does doublet use?
However, the all-band doublet antenna system uses (normally) high impedance parallel transmission line. Small variations in antenna wire length will make no difference to doublet performance or to our ability to match the impedance at the shack end of the feedline.