LBA protype v 2.0

LBA platform version 2.0. Photo: Markku Postila

Here is another prototype of the raised LBA antenna platform designed by Markku Postila and Toivi Iinatti. This one allows arbitrary rotation of the antenna and has easily adjustable legs. The picture also shows the LBA antenna installed on top of the platform.

However, it seems that we will need to extend the ground plane with this type of a design. Recent antenna modeling results by Johan Borg of LTU suggests that this configuration has the effect of broadening of beam significantly at higher frequencies.

NEC model of the antenna with a raised ground sheet.

40 MHz beam pattern of an individual element. Slight broadening at 40 MHz, but nothing too serious.

80 MHz beam pattern of an individual element. The raised platform causes a broadening of the beam and a deeper minima at the zenith.

LBA Prototype platform

The LBA platform prototype, built by Markku Postila and Toivi Iinatti. 

We are now already thinking about the LBA build next year. This will be challenging because we cannot level the field, as it will probably cause erosion and water quality problems with the nearby Siilasjärvi lake, were all the water drains to. We are now focusing on a design which involves similar raised platforms, which hopefully will allow easy position adjustments, when permafrost moves our antennas around. Another reason for the platform is that we will need to use them in order to level out the antennas, if we cannot level out the ground. In anticipation of this, Johan Borg of LTU is currently investigating the effect of such a platform on the beam pattern of an individual antenna.