The 160 m Linearly-Loaded

Inverted-V Dipole

Since the F2 propagation was dropping in the low of the current solar cycle (... but when it has been really open??) I have moved my attention to another exotic radio amateur band: the 1.8 MHz (160m). The 160m resembles in several aspects the 6m: spotty propagation, weak signals, need for educated radio operations and a lot of patience.

While for the 6m I could arrange for a relatively good antenna setup, on the 160m I can not even think about locating a "good" antenna, as I am living in an apartment downtown Roma, and the terrace of the building is just approximately 36 m x 15 m. Therefore I had to find out a suitable antenna for the TB, fitting the available dimensions.

I have been initially thinking about sloping dipoles with concentrated inductance coils or about using the tower as transmitting antenna. However surfing the web, I came across the KG0ZP's web site, where a nice description of the Super Linear-Loaded Inverted V dipole was provided. Went through the description of the antenna and carried out a design compatible with my tower and real estate.

As I have a terrace with two level height, and different lengths I have implemented an asymmetric design: not the best but we have to be pragmatic! The two sides are described in the attached figures while the overall scheme is given in the third figure.

 

The antenna is composed by a 1:1 baloon (used a Fritzel AMA), a sloping part and the linear-loaded section. The wires in this section must be kept at a constant distance by spacers. To the scope I have used a 2 cm diameter PVC tubing of 24 cm which have been drilled on both ends as shown in the drawing at a distance of 20 cm. To keep the insulators in place, I have used some tie wraps which are holding the cable inside the PVC tubes. As conductor I have used an insulated electric wire with section 0.5 mm2 approx. The following picture shows the components just before the place into operations of the cable into the spacers.

It took to me quite a long time to complete the dipole, essentially because of other committments. However in October 2005 I eventually installed the antenna on the terrace, as it can be seen from the following two photographs.

 

With the initial measures, the antenna was resonating at a frequency too high (1.980 MHz), so I had to increase the lenght of the tips up to 7 m in order to bring the resonance down to 1.820 MHz (dimensions provided in the initial photographs are the final ones).