Linked dipole

So, as my first antenna I made a 40M (20meters long) antenna, just to get on the air. after a while the 40M band got noisy in the daytime and I wanted to try out the 20M band. Since my antenna is hanging rather low and I have a pulley systen to lower it down I found that you easily can link the wire to get the resonance you want. So I set out on this project.

First off, I thought why just make it 40/20 ? as the linking is pretty easy I started at 10M with a insulated wire at 2.6meters long at both sides of the center. Everything I talk about doing is done on both sides of the center, they have to be identical, just in case I forget to mention this. A antenna analyzer is a great tool for doing this but it can be done with a swr meter as well. I have a miniVNApro so I just connected this to the center and could easily see where my antenna was in resonance. You will start out with a bit of extra wire as it is much easier to cut off a bit, than to solder it back on. In my case it was a bit long so I took it down again and cut of 1cm of both ends, and pulled it up again and analyzed it. Still a bit long. (cut and try until youre satisfied)

Using a swr meter (maybe built in to you radio?) you will have to make a few steps. first try the frequency you want to be resonant, write down the swr.
Then tune up and down 10KHz and measure swr, you can take more measurements to get the curve more accurately.
Lets say you take theese readings:
7.100 MHZ - SWR 2
7.110 MHZ - SWR 2.1
7.120 MHZ - SWR 2.2
7.090 MHZ - SWR 1.9
7,080 MHZ - SWR 1.8
Well here we see that the lowest reading is downwards, take the antenna down and cut of a little bit. As you see this will take a lot of time.

A way of cheating here would be to calculate out how much to cut of, this can be done by first finding out where the antenna is resonant now, lets call it the Fnow value.
And we know the frequency we want to have resonant the Fwant value.
For this we also need the wire length Wlength value.

How long the antenna should be = (Fnow / Fwant ) * Wlength 

So, my 40M dipole wich i first cut at 10meters was resonant at 6.940MHz but i wanted it on 7.100MHz we put that through the grinder:
6940/7100*10 = 9.77meters | Ok, its 0.23m too long, or 23cm we cut that off both ends and we should be good.

Ok, ive digressed a bit from the link dipole here but its basically the same for all the bands. I started with the 10M band, tuned it to resonance. then I soldered on a small banana socket on the 10M end, and a banana plug on the beginning of the 15M band start. Now you tune the wire for you 15M band frequency, 20M and 40M.

My tuning frequecies:
10M - 28.300MHz
15M - 21.225MHz
20M - 14.175MHz
40M -   7.100MHz

Good luck and HAVE FUN !