Hi Martin, I once looked at the Vishay IL300 (or it may have been an earlier version). My application was isolating a current shunt but we couldn't get the gain or offset sufficiently stable over the temperature range (-20C to +50 ?). IIRC we were looking for <<1%. This shouldn't be an issue with you so it may be worth a look. The package has a transmitter LED and two receive sensors. One sensor is used to correct non-linearities. Your main issue could be frequency response - I'm not sure about that but the data sheet should be available, along with suggested schematics. RP RP On Fri, 16 Nov 2018 at 08:35, AK <00@case.edu> wrote: > 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 y= ou > 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 > > > -- > 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 .