<<

Grounding and de-noising
of my antenna system. pa0nhc 20160928

 


The 55+ apartment complex "De Veldhof" where i live.


Grounding.
The groundings of the equipment only are connected to the steel roof construction in the atrium. The mains dafety ground is not connected.
At the back of the radio table is a grounding rail (ALU strip). All equipment can be grounded to it with low impedance inter connections.
The length of the connection between the rail and the grounding point at the roof is as short as possible (a few meters).
Both measures are effective to achieve "cold" (RF-free) equipment housings.


Lightning grounding.
To minimize damages in case of a lightning strike, both bases of the antennas are connected to the steel roof construction via a 2x20mm2 ALU strip on concrete tiles.

You here can see the artificial ground surface. It consists of 2 cheap rolls 1x25m powder coated galvanized garden fence grid  It is electrically connected to the grounded antenna bas. It is meant to try to shield the antenna from (PLC) noises coming from the apartments below.


De-noising.
With regular intervals ferrite clamps are placed on the cables  In the concrete roof beneath them run noisy mains cables. These clamps prevent these noises to run towards the antennas or the radios. If the distances between clamps is kept small, they also prevent induction from, and re-radiation of transmitted signals. The radiation patterns of the antennas then are not influenced.


Directly beneath (also inside) the loop tuning cabinet are ferrite clamps on the cables. These are important, as they prevent that mantle currents on the coax  and wires reach the loop impedance transformer.
In the cabinet also is the first line filter in the drive line for the tuning motor, and a 5W heater which prevents condensation forming.


The base of the VHF mast.
To prevent leakages and damage to the roof isolation, the pebbles are carefully removed before the base is placed. Concrete slabs are placed in/on the bases to prevent movements. The antennas are stabilized by guy wires.
The ALU grounding strip is screwed onto concrete tiles, which also insulate it from the roof surface.
All connections to aluminum were protected against corrosion wit spray Tectyl.
Concrete tiles on top of the coaxes prevent movement in heavy wind.


The most important point :
Grounding of coaxes to the steel support of the atrium roof.
Surge arrestors in the coax lines are mounted on an aluminum L profile.
REM: the correct direction of fitting is important.
The box contains a second tuning motor line filter including over voltage diodes.

This grounding point is inter connected to the complete steel construction and to groundings via every concrete wall. Noise free and best point for lightning grounding.


Double action over voltage diodes reduce induced voltage spikes from lightning. Chokes block HF noises.

Both coaxes enter through an insulating wall. They end on an aluminum L-profile which serves as a central ground point. A thick piece of cable connect it to the ground rail on the back of the radio table.

The power supply contains ground-leak-switches. To prevent noises on the mains safety ground wire enter the radios, this "safety ground" is disconnected. All equipment is only connected to the ground rail and the grounding from the roof.

The best (expensive) solution should be the use of a separating transformer and a heavy duty mains filter.

The black box contains a third loop motor line filter. The automatic loop tuner (the aluminum box with LEDs) is connected via a XLR5 plug.