As the propagation conditions getting worse for 15 m and 17 m, I extended my linear loaded dipole on both sides by 1.8 m in order to cover the 20 m band. SWR is ok without modification of the 1 : 4 transformation line.
Will see, how it works in the upcoming CQWW DX CW contest.
In Singapore space is limited, and in our appartment it is difficult to setup any HF antenna. Our balcony is the only place where I have a space to mount something. Even there, officially nothing is allowed to extend out from the building.
I decided to setup a simple vertical, using a telescopic fiberglass pole, which I can pull out temporarly, when it is getting dark. The pole has a total length of 10 m, approx. 1 m (the lowest segment) safely mounted to the balcony railing and sidewall.
Continue reading Fiberglass Balcony Stealth Antenna for 40 m
For my amateur radio activities on the HF bands I only have a 3.6 m wide balcony available for antennas. After some study I decided to experiment with a shortened dipole for the 15 m band. The full size 21 MHz half wave dipole would require a span of approx 7 m, therefore I searched for a solution to shorten the full size length by 50 percent.
Finally I decided for a linear loaded dipole; the layout and resulting dimensions are shown below.
First measurements at the resonance frequency showed a low input impedance at the dipole’s feed point with values around 10 Ohm. The theoretical radiation resistance of a 2 x 1.6 m short dipole would be 10 Ohm, so it is an indication of low losses in the system. In order to match the antenna to the 50 Ohm of the transceiver, I use a quarter wave transmission line transformer consisting of two parallel connected 50 Ohm coaxial cables.
After fine tuning the length of the antenna wires, I achieved an SWR below 1.5 for the CW segment of the 15 m band.
The antenna’s bandwidth is around 200 kHz; I could already work DX stations around the world.
Dipole feed point and 1:1 balun
