I mean the interface to the computer has a transformer. You don't connect straight to the I/o of the radio from a computer.
Best regards - Brian Carling AF4K Crystals Co. 117 Sterling Pine St. Sanford, FL 32773 Tel: +USA 321-262-5471 > On Sep 10, 2014, at 10:03 PM, "Scott Johnson" <[email protected]> wrote: > > Checked three sound cards, and a motherboard with built in sound, not a > transformer in the group. They all had a little stereo line driver IC. > > Scott W7SVJ > > -----Original Message----- > From: Boatanchors [mailto:[email protected]] On Behalf Of > Brian Carling > Sent: Wednesday, September 10, 2014 6:39 PM > To: Jim Simmons > Cc: [email protected] > Subject: Re: [Boatanchors] 2nd Newbie Q Follow Up > > Speaker output from a computer sound card is not high impedance nor low > level. > > Also most have transformer isolation so ground loops are not usually an > issue. > > Best regards - Brian Carling > AF4K Crystals Co. > 117 Sterling Pine St. > Sanford, FL 32773 > > Tel: +USA 321-262-5471 > > > > >> On Sep 10, 2014, at 5:26 PM, Jim Simmons <[email protected]> wrote: >> >> The reasoning behind grounding only one end of the shield is to prevent > "ground loops". In high impedance circuits ground loops will introduce > oscillation into the signal chain. In audio circuits this presents itself > as whistles, howls, and distortion. >> >> For example: the shielded cable in an audio amplifier that connects the > input jack on the amplifier to the hi gain preamp circuit should be grounded > only on one end. Chances are the input jack is already grounded to the > chassis by its mechanical connection, and the input preamp stage is also > grounded to the same chassis by an electrical connection. So the signal > return path already exists without connecting anything. >> >> When you connect a shielded cable (inside the amplifier) from the jack all > the shield on the cable is for is to shield the inside signal wire from > external influence. If you connect both ends of the shield you now have two > return paths for the input signal (the chassis and the shielded cable), and > these two paths will be different in impedance, (capacitive and inductive) > This difference can (and usually does) make up a tuned feedback circuit for > the preamp - which turns it into an oscillator. >> >> If you're connecting two things together that do not share a common > chassis (common ground) then both ends of the shield must be connected to > form a complete path for the signal. If you have items daisy chained > together and their cases are made of metal then if two, or more, is allowed > to come in contact (creating another return path for the signal) then you > just may find that you will have howls and or distortion. >> >> The way to find out if you need to only connect one end is to connect both > ends and try it. It it works, then fine. If you have unwanted distortion > then disconnect one end. I don't think it really matters which end the > shield is grounded on, but I would ground it on the input (jack) end. >> >> By the way, the above also applies to rf circuits but in spades. >> >> >> Hope this helps. >> >> Jim, N5MSJ >> >>> On 9/10/2014 12:09 PM, Brian Carling wrote: >>> I still don't know what devices you're trying to connect together. > However most devices I have used do not have any difficulty with this > arrangement and grounding the Shields at both ends. >>> >>> Best regards - Brian Carling >>> AF4K Crystals Co. >>> 117 Sterling Pine St. >>> Sanford, FL 32773 >>> >>> Tel: +USA 321-262-5471 >>> >>> >>> >>> >>>> On Sep 10, 2014, at 12:15 PM, "Bob Jackson" <[email protected]> > wrote: >>>> >>>> Ah, Ha! You've hit on the issue! >>>> >>>> I'm trying to convert the stereo audio output from a 1/8" jack (e.g. > iPod) to two RCA plugs to go into a switchbox. On the surface, it would seem > that the shield should be the common connection between the two RCA plugs. > Using the shield and one signal wire for one plug is OK but when I go to the > second signal wire, I find that it's actually common to the shield itself. > It doesn't seem right to leave the shield unconnected at this second plug > but to connect it would seem to mean that now the two signal wires are > shorted together. What's the story here? >>>> >>>> Bob AG5X >>>> ----- Original Message ----- From: "Brian Carling" <[email protected]> >>>> To: "Bob Jackson" <[email protected]> >>>> Cc: "porch.boat" <[email protected]>; "puck.boat" > <[email protected]>; "qth.boat" <[email protected]> >>>> Sent: Wednesday, September 10, 2014 10:49 AM >>>> Subject: Re: [Boatanchors] 2nd Newbie Q >>>> >>>> >>>> What two devices are you connecting? >>>> >>>> Best regards - Brian Carling >>>> AF4K Crystals Co. >>>> 117 Sterling Pine St. >>>> Sanford, FL 32773 >>>> >>>> Tel: +USA 321-262-5471 >>>> >>>> >>>> >>>> >>>>> On Sep 10, 2014, at 11:29 AM, "Bob Jackson" <[email protected]> > wrote: >>>>> >>>>> I've noticed that some construction articles involving the use of > shielded cables advise that the shield be connected at only one end but they > don't say which end, i.e. near or far. Also, when is this practice most > useful and why? >>>>> >>>>> Thanks again, >>>>> >>>>> Bob AG5X >>>>> _______________________________________________ >>>>> Boatanchors mailing list >>>>> [email protected] >>>>> https://puck.nether.net/mailman/listinfo/boatanchors >>> _______________________________________________ >>> Boatanchors mailing list >>> [email protected] >>> https://puck.nether.net/mailman/listinfo/boatanchors >> >> _______________________________________________ >> Boatanchors mailing list >> [email protected] >> https://puck.nether.net/mailman/listinfo/boatanchors > > _______________________________________________ > Boatanchors mailing list > [email protected] > https://puck.nether.net/mailman/listinfo/boatanchors > _______________________________________________ Boatanchors mailing list [email protected] https://puck.nether.net/mailman/listinfo/boatanchors
