28-06-2019, 08:03 AM
Terry
The 'old' technique was to have a direct RF earth which was to include a high-current plate-style mica capacitor in series to the earth stake. The capacitance value was chosen such that it was a high impedance/reactance at 50Hz but low at the lowest frequency in use (160m ?). That way there was no issue with corrosion etc due to multiple earth points and distributed 50Hz current.
The problem is two-fold though. The best style of flat mica sheet capacitors are no longer available - at least new. The second point is that unless that capacitor style goes short-circuit in the presence of a nearby lightning strike, it won't protect your gear. If it is blasted into smithereens by the initial surge current, where is the next path to ground going to be ? Notice I don't mention a direct strike above - nothing really helps then, except contents insurance !!
I have a 1.8m copper-clad rod just outside my shack building and it is fed via a short-as heavy conductor (thick-ish flat bar is best) through the wall to a continuous strip of aluminium angle screwed along the back edge of my shack benchtop. All the radio gear is then connected via flattened RG213 braid pieces onto 1/4" countersunk screws set upside down into the aluminium angle and tightened down with wing nuts. It is not a capacitor-isolated RF-earth but I figure that it will outlast me even if corrosion occurs.
The shack coax cable entry mounting strips also get returned to the aluminium angle section - although I do not expect any of it will survive a direct strike. Certainly provides a reasonable grounding effect at HF though.
Doug
The 'old' technique was to have a direct RF earth which was to include a high-current plate-style mica capacitor in series to the earth stake. The capacitance value was chosen such that it was a high impedance/reactance at 50Hz but low at the lowest frequency in use (160m ?). That way there was no issue with corrosion etc due to multiple earth points and distributed 50Hz current.
The problem is two-fold though. The best style of flat mica sheet capacitors are no longer available - at least new. The second point is that unless that capacitor style goes short-circuit in the presence of a nearby lightning strike, it won't protect your gear. If it is blasted into smithereens by the initial surge current, where is the next path to ground going to be ? Notice I don't mention a direct strike above - nothing really helps then, except contents insurance !!
I have a 1.8m copper-clad rod just outside my shack building and it is fed via a short-as heavy conductor (thick-ish flat bar is best) through the wall to a continuous strip of aluminium angle screwed along the back edge of my shack benchtop. All the radio gear is then connected via flattened RG213 braid pieces onto 1/4" countersunk screws set upside down into the aluminium angle and tightened down with wing nuts. It is not a capacitor-isolated RF-earth but I figure that it will outlast me even if corrosion occurs.
The shack coax cable entry mounting strips also get returned to the aluminium angle section - although I do not expect any of it will survive a direct strike. Certainly provides a reasonable grounding effect at HF though.
Doug
Doug VK4ADC @ QG62LG51
http://www.vk4adc.com
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http://www.vk4adc.com
This Forum is only going to be as interesting as the posts it contains.
If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.