[Boatanchors] Isolation Transformers for noise reduction

[Bill Cotter]

There is an auction for up to ten TOPAZ Ultra-Isolation 
Transformers part number 91091-11 (125VA 120/240V) listed at $90 
(or, make offer) + $14 shipping. I just purchased one after 
offering $50, for a total cost of $64. The 91091-11 retailed for 
between $250-300 new, and is superceded by the 91091-T31 series.

321059789702

These are medical grade (shielded) isolation transformers with very 
good attenuation of harmonics specifications (common mode reduction 
= 146dB, normal mode = 65dB) above 100kHz - just right for keeping 
switching trash on the AC line from getting into the radio power 
supply.

Specifications:
http://www.pacificparts.com/vends/mge/images/t1.pdf

73 Bill N4LG




At 06:04 AM 4/18/2014, you wrote:
>Hi Bill,
>
>Thanks for the info...I went and had a look at the Topaz 
>transformers on ebay. They look very interesting! I've gone off 
>the idea of the Sola transformers because of their no-load current 
>draw, heat and noise. I do like the concept of balanced power but 
>I'm concerned about their use in the home...I haven't found any 
>literature on balanced power in electrical building codes. So it's 
>possible there may be insurance issues should the worst ever 
>happen. But, I tend to think too much and I'm sure they are 
>perfectly safe.
>
>I'll look more into the Topaz transformers. I'm not worried they 
>don't regulate the AC because as you say...my main goal is noise 
>rejection.  I'm looking for something that is safe, reliable, 
>quiet, efficient and good at AC noise reduction so I appreciate 
>the heads-up on the Topaz.
>
>Best 73
>Ken
>ZL3AA
>
>On 18/04/2014, at 11:20 am, Bill Cotter <n4lg at qx.net> wrote:
>
> > Ken,
> >
> > For a true isolation transformer, search Google and eBay for 
> Topaz isolation transformers. Topaz (Square-D) manufactures 
> medical grade (<100uV leakage pri-sec) shielded isolation 
> transformers designed to prevent electrical shoch to patients 
> when connected to EKG, EEG, electrocuatery, etc. They are VERY 
> good at isolating line noise from low signal devices. And, they 
> are very inexpensive on the used (eBay) market.
> >
> > Unlike Sola transformers, they do not regulate the AC, which is 
> not a downside since noise rejection is your goal.
> >
> > 73 Bill N4LG
> >
> >
> >
> >
> >
> >
> >
> > At 06:10 AM 4/15/2014, you wrote:
> >> 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