[R-390] Isolation Transformers, GCFI and Balanced Power

[Ken Harpur]

Good evening list,

Here's something for everyone to get their teeth into...

I'm having issues with the line filters in my R-390As tripping the GCFI (doesn't everyone now?)...It doesn't happen all the time but it's a lottery every time I plug one of them in on whether it will trip or not. One filter is bad so it has been removed, awaiting a replacement. I've been all through the archives looking for ways to overcome the problem. I had intended to open them up and rebuild them with smaller value caps, then I came across a post saying that the filters could be left intact and the radios plugged into an Isolation transformer. The Isolation transformer will prevent the GCFI from tripping...

Hmm...yep seems fair enough and I have a 230 to 115V transformer here so it's do-able. I could re-wire the power supply on one radio to 115V and try it out.

So then I go away and infest google for a few hours trying to find info on any Hams or serious SW DXers that run their boatanchor equipment through isolation transformers. Most results were referring to audio isolation to prevent ground loops but nothing on Line Isolation Transformers. All the hits that dealt with AC mains isolation transformers were for the audio guys and recording studios where they talk about Balanced Power Transformers. It seems Balanced Power is used extensively in recording studios and the concept/theory behind this is solid. We even use the same concept in radio...balanced antennas, balanced microphone and audio cables etc. I'm curious if this concept has be embraced in our radio shacks as far as cleaning up the garbage on our mains?

I can hear many different 'dirty' signals tuning around the bands on any of my R-390s...switchmode power supplys, computer screens, the TV upstairs, neighbour's washing machines etc. I had good results by moving the antenna and better quality coax. My reasoning is if the antenna can pick up these signals then the same garbage is all over our line supply as well. I realise the line filter was installed on these radios to keep signals from radiating out of the receiver via the line cord, as well as keeping common-mode interference on the line from entering the receiver...so the idea has been around a long time.

Google gave me no answers regarding Balanced Power use radio reception situations...maybe there might have been something if I read through over 1000 pages but..."Aint nobody got time for dat!"

So what do you do to mitigate noise on your line supply, if anything?

Kind regards,
Ken