In CQWW 160m we are planning again a serious participation. This time we want to errect a 2el vertical Array for 160m towards the US. In this post you will find some detailes regarding our unique situation and some design thoughts.
ED1R Contesting site
Even while having more space than the average ham, at ED1R we are restricted when it comes to lowband antennas. Our 80m and 160m antennas have to be installed the day before the contest and be removed the night after the contest. Fortunately the friendly neighbors allow us to use their fields during the weekends. Here is a 3D model of the ED1R contest station. Note the two (brown) areas which mark the fields we can use for our 80m / 160m antennas.
Hight is everything
When it comes to 160m, vertical antennas are hard to beat. During the last year we used sucessfully (subjectively measured) a 15 tall inverted L-Antenna. The L-Antenna is a poor man’s T-Antenna. The reason is because the L-Antenna has a rather significant high angle radiation which is usually not desired. On the other hand, the equally long horizontal wires of a T-antenna cancel effectively the high angle radiation.
On 160m a Lambda/4 radiation is almost 40m tall. This results in an antenna radiation resistance of 36 Ohm. Unfortunately it is impossible for us to errect a 40m tall antenna. The maximum height is defined by our 18m tall Spiderbeam poles. The main problem with verticals lower than Lamdba/4 is that the antenna radiation resistance decreases. With a low antenna impedance it is extremely important to have an excellent ground (radial) net. Otherwise, most of the power will be lost in the earth.
There are several ways to make a 18m tall antenna resonant on 160m. Here are some of the more popular designs:
- Adding an inductor at the feedpoint
- Extending the antenna with a horizontal wire (L-antenna)
- Adding a slooping T-hat
- Adding a horizontal T-hat