28-06-2019, 02:34 PM
Should one wish to isolate the RF earth from the mains earth with capacitor as Doug suggests, it's quite easy to fabricate a suitable capacitor. I've measured the capacitance of an A4 sheet of aluminium insulated from the roof of my car by a thin sheet of Mylar. The aluminium sheet was held in place by several magnets. The measured value was 6nF. That works out to be 530 kOhm of reactance at 50Hz but just 7 Ohm at 3.5 MHz [This was my very effective, non-invasive earth connection for a HF mobile whip mounted on a roof rack]. It's quite feasible to interleave a few such sheets of aluminium (or copper or brass if you prefer) with Mylar film sheets to achieve proportionally higher capacitance. The main thing is to ensure the sheets are tightly clamped together in order to maximise the resulting capacitance.
Voltage rating is not an issue. As Doug suggests, should a lightning strike occur, it's a good thing for the dielectric to vanish, and in any case, a solid bolt of lightning will destroy anything in its path.
Chas
VK3PY
Voltage rating is not an issue. As Doug suggests, should a lightning strike occur, it's a good thing for the dielectric to vanish, and in any case, a solid bolt of lightning will destroy anything in its path.
Chas
VK3PY