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Let me inject here...The hydrophones and voice transmitter for the system I work with are not shielded either and yes when indoors 60 cycle humm is a problem but not outside. Also, when I talk over the "b" or transmit channel, some cross talk does make it to the listen or "a" channel even though this channel is inhibited during periods of transmision. This is because I failed to use shielded cables within the electronic enclosure themselves. Although I have suceeded to a great degree, I'm still learning too. David Bartsch > From: wreckdiver@frontiernet.net > To: personal_submersibles@psubs.org > Subject: RE: [PSUBS-MAILIST] RFC - Standard Thru-Hull Electrical Connector > Date: Sun, 20 Dec 2009 14:35:46 -0500 > > Sean, > > You bring up a good point and something I hadn't fully thought through. You > are correct that the cable shield would be better connected to the sub hull > so that the penetrators would not need to be isolated. > > It's interesting to note that after looking at Dan Lance's OTS units, they > are using plain old RG-58 coaxial cable and while the cable itself is > shielded, they are using the shield as just one of the signal lines to the > transducer. I did notice the transducer picked up a fair amount of 60 hz > signal from the power lines in his apartment. This obviously wouldn't exist > out on the water but may indicate a susceptibility to sub motor noise in > addition to possible ignition noise from the surface tender engine. > > Al > > -----Original Message----- > From: owner-personal_submersibles@psubs.org > [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Sean T. > Stevenson > Sent: Friday, December 18, 2009 8:22 PM > To: personal_submersibles@psubs.org > Subject: Re: [PSUBS-MAILIST] RFC - Standard Thru-Hull Electrical Connector > > Al, do you mean to suggest tying the shield to the safety / chassis > ground, or to the electrical supply common? ABS etc. require that the > entire DC system be ungrounded - that is, that the battery negative / > supply common is not to be connected to the hull or equipment chassis. > For maximum RF rejection in a shielded cable, that shield must be > continuous through the shell of a metal connector. Tying the shield to > the DC common would necessitate ensuring that all penetrators / > connectors remain electrically isolated from the hull, lest they connect > the DC common to the hull in violation of the Rules. Would it not be > better practice to connect all cable shields, connector shells and > equipment chassis together to form a contiguous RF shield while > retaining isolation from the DC common (or, if the twisted pairs are > individually shielded, tying the individual pair shields to DC common > through a pin in the connector, but keeping the overall cable shield > isolated and connected to the connector shell)? > > I'm not really an electrical guy - I'm genuinely curious. > > Sean > > Al Secor wrote: > > > > Alec, > > > > A couple of comments.. > > > > # 5. Although Piezoelectric ceramic transducers do have polarity, > > since we are feeding them with an AC signal then this is not an issue. > > For noise considerations we may want to consider a shielded twisted > > pair with the shield grounded to the sub's electrical ground. > > > > > > > > ************************************************************************ > ************************************************************************ > ************************************************************************ > The personal submersibles mailing list complies with the US Federal > CAN-SPAM Act of 2003. 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