Isolation of Ground Differentials and USB Interfaces

[Rabbitz]

Hi VK4TMH,

I thought you may have been 'one of us' from your answer.

I have two earth stakes outside the shack, they are tied with 4mm diameter wire to a common rail at the back of the bench. Everything radio related, including the antenna barge board pole, is tied in there.

I haven't bonded it to the mains earth as the bond point and stake are a fair way away and hard to get to. I might try a couple of experiments as the main switchboard is adjacent to the workbench.

I doubt it will make much difference to the noise floor. 60m away is a power transmission stanchion from which I can lie in bed and listen to the crackle and pop across the insulators as well as railway line 100 or so metres away. We've had a little rain so it is worse. We need a big squall to clean the insulators. Even if I can't hear it, I know it is there when I plug in my Strat copy, it somehow knows we are in the transmission line magnetic field...

73 DE VK2CSW

[Marcel]

I haven't bonded it to the mains earth as the bond point and stake are a fair way away and hard to get to. I might try a couple of experiments as the main switchboard is adjacent to the workbench.

A connection point to the earth in the switchboard is ideal. Actually, according to AS3000 and for the majority of pro radio installs it is the preferred way. If using a switchboard earth make sure you include adjacent to and external to the mains switchboard a disconnection point that is labelled as 'Equipotential bond' to fully comply. You can use whatever wire you like on the station side of the EP bond junction, but from the EP bond junction into the switch board it must be the standard Green/Yellow electrical wire stuff of a size equal to (or greater than, or up to 35mm) the largest earth wire within the board. In Australia a qualified and licensed electrician is required to fit/wire the EP junction into the mains power switchboard, but the connections to the station side of the EP bond can be done by qualified radio operators. The EP bond junction should be obvious, labelled, adjacent to and easily disconnect-able by any sparky working on the switchboard..

In a typical house that would be 4mm or 6mm. In many hill top radio sites that could be 16mm. In large radio sites that are built using 70mm everywhere and then extra 75mm runs for lightning protection the EP bond max's out at 35mm as often the MEN for that site will only be a 35mm cable.

Over the years I've grown to love a good decent well designed Earthing system. Not just for radio but there are noise benefits in the audio and guitar world too. In my case the workshop has a 35mm EP bond point (AS3000 type 1) as I requested it when I paid for a sparky to wire up my away from the house huge big 3 phase ready (and expensive) shed, so I can be working on a SCR type lighting rig while soak testing a guitar amp for a evasive 'crackling' noise. The house has the 4mm EP bonding wire on a 2nd clamp on the MEN earth stake as nil sparky was involved or required (AS3000 type 3) and the wife doesn't bother me about her TV reception while I'm chatting on 40m in the next room...