A vertical dipole for 7MHz (and 21MHz)

For a while I have been planning on my next simple antenna project. I have the high trees, that I can utilize, as I did with the folded dipole. About 40 meters from my house there is a high fir tree, maybe around 30 meters high. I'm not afraid of climbing, so I decided to make a vertical dipole for the 7MHz (40 meter) band. Also I hoped that could help me getting a good antenna also for 21MHz (15 meter band), since according to the theory, a half-wave dipole for 7MHz is a 5/8 wave dipole for 21MHz. 5/8 wavelength tune well to 50 ohm impedance, ant at least when it comes to ground plane antennas, 5/8 means a low elevation angle for the radio waves. And this means DX.

Here is the starting point. 

I prefer factory baluns, since they are robust and durable. The antenna wire is plain old phone wire.

A half wave dipole is very simple to construct. IAround 10,5 meters of wire in each leg.

Temporary location at a height of 2 meters.  

I hang up the dipole horizontally at the height of 2 meters, in order to get an initial measure of the SWR, which was 3:1. After cutting, it was around 2:1, so I decided to stop cutting (after the lesson learned with the folded-dipole project). Yes, I had to try a QSO with this temporary antenna installation, the dipole legs hanging indefinitely at 1,5-2 meters. No problems: Europe hears me and I hear Europe. But...what about the DX, which I have never been able to catch on 7 MHz? Up in the tree!

Up in the tree, at around 25 meters. I took a camera with me, in order to document the views from the fir. There...far down, is my excellent folded  dipole.

Nort-west view from the tree. Yes, still some snow everywhere, and the leaf trees seem dead...we are in Finland, right?

North-east view from the tree. In the summer the views aren't this open because of the leaves. Let's see how it affects the performance of the antenna.

When I got the wire in place, the balun was hanging at about 12 meters and the 10 meter legs up and down from there, I was warm and sweaty.

The results:
After the shower I started my radio. The SWR was little less than 2:1. Not much, but anyway I decided to use my antenna tuner. The 40m band sounded crystal clear: almost no noise, only strong and clear CW beeps. And the digimode waterfalls looked brilliant...I compared these to the windom antenna, which is installed at about 8 meters...the difference is remarkable. Boy, I was excited!

There was the Japan International DX contest going on...let's check. I heard many Japanese stations right away. When I swithed back to the windom, the stations went weak again. Well, my antenna looks promising. I answered a CQ from JH4UYB (Japan)  and he heard me immediately! He didn't get my call 100% at the first try, but after a couple of repetitions we could finalize the QSO. Obviously this guy is a big gun, with strong power, giant listening and sending antennas, but anyway: my wire vertical dipole works can perform DX. the propagation conditions were not superb at all, so there is still lot to explore with this installation. (Later I might arrange the antenna as a sloper, or even horizontal dipole...let's see.)

Also the Europeans are now delight to work...my fellow hams report strong and clear signals and I hear them clearly. And the waterfall display on the digimodes does not look "noisy" anymore: When switching between the new antenna and the windom, there is a remarkable difference in the noise floor in the specrum view. No windom again on 7MHz, that's for sure!

What about 21MHz? 
Guinea-Bissau and the States were worked almost immediately. Just a few QSOs made, but this looks promising. Also, I'd like to check this 5/8 wave stuff with Eznec simulation: what were the theoretical elevation angles with a vertical dipole like this?