Martin, I built what you are looking for back about 12 years ago using optical methods. Using an analog to TOSLINK converter (I have extras if you are interested), I modulated a laser instead of the LED in the TOSLINK connector, and sent the audio over free space to a receiver. The sound quality was perfect (no loss of highs I have experienced from transformer isolators) and fun. You would just need to find a piece of equipment with TOSLINK input. On Thu, Nov 15, 2018 at 9:20 AM Martin McCormick wrote: > "Brent Brown" writes: > > A proper optical fibre link should perform better than copper + > > optocouplers. Will for > > sure be something commercially available... probably at commercial > prices > > :-( > > Thank you to everybody who replied. > > Dwayne Reid writes: > >The standard approach is to use an audio isolation transformer. I > >have had very good success with issues such as what you are describing. > > > >Shameless plug: my company sells little isolation transformer modules > >for not much money. These use a semi-custom transformer from > >Datatronics and really do work very well. I think that cost is > >around Can $25 in singles (soon to increase due to supplier cost > >increases) plus shipping. > >Let me know if you want to try this out. I'll arrange to send one to > >you and you can either pay for it or return it as you see fit. > > That is quite reasonable and thanks for the information. > > You got me to thinking, though, and I have a large spool > of CAT 3 cable which would provide 4 twisted pairs of telephone > wire. I do have some little 1-to-1 isolation audio transformers > so the only problem would be if the windings of the transformer > capacitively coupled the low-level EMI smog in to the radio. The > common mode signal in this case is the low-level RF noise while > the differential signal is the desired audio. The noise > shouldn't make it across the transformer unless it does so via > capacitive coupling. I'll just have to try it and see. > > The fiber optic approach that Brent Brown describes would > be a great solution as there would be nothing conductive between > the ends of the cable. I imagine the best fiber optic link would > be either a digital carrier made by pulses of light at some high > sampling rate such as 10 Mb/S or so with a decoder back to audio > at the other end but then you get the possibility of your digital > link generating more noise to have to deal with which totally > defeats the purpose. > > Before I retired in 2015, I worked at Oklahoma State > University in our Network Operations Group which managed our > Ethernet and telephone networks on campus and the links to our > auxiliary campuses and the Internet. > > The thing that impressed me about fiber optics is that > the fiber isn't that terribly expensive but terminating it is. > > You've got to polish the cut end of the fiber until it is > optically flat and free of deformations or one must use an > electric arc to melt two ends of fiber such that they fuse > together creating one continuous fiber. Equipment that will do > that reliably is quite expensive. Some of the consumer HiFi gear > that uses fiber-optic audio cables may use plastic fibers for all > I know but still terminating them is not trivial. > > Basically, if the fiber optic connection is meant to be > easily connected and disconnected, you polish and lose 2 or 3 DB > per interface or you fuse if you are permanently joining a fiber > to something that you don't plan to remove under normal > circumstances. Those fusion splices don't have any loss since > there is no boundary. > > In this case, thanks to all. I'll temporarily connect > the audio to a short jumper and the isolation transformer and > then the long line from the secondary of the transformer to the > audio mixer and see if the smog survives all that. If it does, > it's back to the drawing board for something different. > > Martin McCormick WB5AGZ > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .