Some scale modeling was done at about 450 MHz with a VNWA to verify the MMANA calculations, in particular the effect of "fat" radiator and top loading.

Various radiators were tested, with length/diameter ratios in the range of about 210....11. The copper plate on the photo represents the ground. These scale models perform amazingly well, even inside the bunker.

The first step was making an electrical connection to the bunker rebar, which has a top area of is about 15 by 30 meter.

Here is Ed is welding a "ground rod" to the rebar.

Ground resistance was measured. It proved to be relatively low, which is good.

As a first test, a single vertical wire of about 18m was connected. On the first CQ on 80m the RBN reported 8 dB S/N in Australia.

Next, we worked VK0EK on 80m almost immediately.A video of this QSO is on line. The TL tube clearly shows the antenna current - proving that this current also flows into the rebar.

A choice was made for a square 4-wire cage type radiator of about 16.5 x 0.5m, plus a top load akin the famous Radio Veronica ship.
As radiation resistance is low (about 10 Ohms), the currents are relatively high (design is up to 10 A). To cope with skin effect, the wires etc. must be relatively thick.

As the calculations show that the construction will work for both 160m and 80 m (being shorter and longer than 1/4 wave respectively), the idea is to make 2 different matching networks to match the antenna to 50 Ohms on both bands.

The photo shows the finished match box, which starts with a 50:50 Guanella balun to force symmetrical currents and hence prevent radiation from the coax.

Followed by a relais to select the frequency.

Left is 80M and right 160M
80M has a L/C, 160M a C/L matching network.

At the top a relais. This relais follow the lower relais.

The center wire is the groundbus.

A first plot with the 160M match in place.

A complete overview of the work done so fare. Photo's will be updated the upcomming weeks.

Last update 16-7-2016.