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...

[Rabbitz]

Well did some experimenting.

It turns out that my big ol' linear power supply was creating a 'bond' between Station Ground and Mains Ground all along.

The chassis of the PS is earthed to both, which rendered any other experiments meaningless.

[Marcel]

A Linear is something I don't have ATM.... Possibly getting an old Yeasu 1kW unit in the coming months but not holding my breath.. so 'barefoot' is operandus normalus for me for the past 30 years...

It is a good thing that you found that grounding point in the PS... Can't imagine the earth loop dramas possible if you had installed another more desirable and permanent EP bond.

[Rabbitz]

When I say linear I mean the power supply is linear (old fashioned tricky dicky transformer/rectifier) as opposed to a linear amplifier.

[Marcel]

The joys of the language we speak and almost write...lol...

I had images in mind of a big metal transformer laden box that fed an excited yet solid stream of electrons into a separate magic box of tube filled RF wizardry that sat neatly between a string slung in the air and a microphone equipped RFI generator... lol. Okay, there is nil Wizard box. Doesn't change things though.

You get used to certain terminology, hear people rightly or wrongly use different words, it is only when many repeatedly say the same things that some of it sinks in... I'm used to 'linear mode power supply' or 'switch mode supply' or 'regulated supply' or 'basic filtered supply' for the various modes of DC generation. And when talking about a 'afterburner' simply calling it a 'linear' or more correctly saying 'linear amp'.

No skin broken, nil blood or tears...it's all good...

[Rabbitz]

Ahh yes, two people separated by a common language.