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PME and RF earths (No replies)

7 days ago
Neil 7 days ago

Hi there,


I spent most of the past few afternoons reading about PME earthing systems and the problems with installing an RF earth, but although I think I understand a little more, I don't think I have a solution to my problem.

I have a modest station consisting of an FT891 and LDG tuner, into a EFHW for 40/20/15 and 10m. The antenna is currently strung around my attic but will shortly be up outside. 

My house is PME earthed and I understand that under certain fault conditions, if I had an RF earth installed, that my station could effectively become the earth path for all properties on the same PME system. 

It is not practical for me to disconnect my 'shack' from PME and run a dedicated earth for it. It is also not practical for me to connect my RF earth to the PME bonding point.

I thought I may run my rig off of a leisure battery, thus eliminating the whole mains supply/earthing scenario.

Then it struck me that there was no difference to doing this than running from a mains supplied 13.8v DC supply-if the DC output was floating. I have a small 6A PSU (which won't be suitable) and having checked this there is infinite resistance between the mains earth pin on the plug and both the +ve and -ve DC out. There is 1.6mV PD between mains earth and the -ve output terminal and 2.5mV between mains earth and the +ve output terminal. I believe all of this suggests that the output is isolated from the mains earth.

I checked my 30A PSU but with this one there is a minimal (0,6 ohm) resistance between the earth pin of the mains lead and the - ve output terminal. Also between the -ve terminal and earth there is a 13.78v PD. I believe this means that the DC output is not floating and therefore if I were to connect an RF earth to my rig, whilst powered with my 30A supply, under certain fault conditions my station would be 'live' as everything earthing through the now failed PME would now earth through my station.

Question 1. Is all of the above correct?

Question 2. If I find a suitable power supply that fulfills all of the above criteria relating to the 6A PSU, is that enough to isolate me from the PME system and allow me to connect an RF earth (and earth my antenna?)


Thanks in advance for any advice


Neil 2E0CMN






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