-----Original Message-----
From: Al Secor <wreckdiver@frontiernet.net>
To: personal_submersibles@psubs.org
Sent: Sun, Dec 20, 2009 2:35 pm
Subject: RE: [PSUBS-MAILIST] RFC - Standard Thru-Hull Electrical Connector
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.
>
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