Wednesday, 6 June 2018

Antennas down

Today was the Swedish national day and off work so I spent it lowering and removing all antennas.
Started in the morning and 2 hours later all antennas was removed and stored away.

Antennas lowered

All antennas removed

Measured the present stacking distance and it seems like its slightly to large as I suspected and according to the simulation of the antenas earlier.
My plan is to stack them using 283 Ohms open wire lines constructed of 6 or 8mm aluminium tubing.
Have looked at Nando I1NDP's antenna feeding and will I like the concept and I did some simulations of my 8 antennas.

Feed simulation

This feeding will give 100 Ohms impedance in the center Point of the 8 antennas but I will use a impedance transformation balun to correct for that and it is present in the simulation as the 70,5 Ohms transmission line.
Simulation results are very good with good bandwidth.

Simulation result including 100 to 50 Ohms transformer

The transformer will be built using a 40mm square tubing with 2 mm wall thickness and a 12mm round tube inside and this will get very close to the needed 70,5 Ohms.

Balun simulation

Will start with cutting of the antenna element and drilling of the booms next week and change the stacking distance to fit the new dimension.
Will also measure all cables that was used as a few of them seems to had moisture inside the connectors and measure all antennas prior to the drilling to check the performance after the winter.

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