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RE: [PSUBS-MAILIST] Passive sonar
Thanks! Will try this next time the sub goes in the water, although I
have no idea when that might be. I think at that point either I'll have
a working sonar in the boat, or a non-working sonar to get rid of.
:)
Alec
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From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Sean T.
Stevenson
Sent: Tuesday, September 18, 2007 5:21 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Passive sonar
Alec - I'm starting to suspect that noise is not your problem, but I
have a few
comments:
1) I don't think you can find braid sheathing intended to be a signal
shield that you can fish a cable through. You can run your cable
through metallic conduit (pipe, or steel / aluminium flex condiut -
exposed or PVC coated) and ground the conduit at one end. For such a
short run, I doubt that shielding is the issue, though, unless you are
dealing with low voltage digital transmissions at high data rates.
2) The cable length doesn't do anything for you. All it does is
increase the voltage drop over the cable (not significant over 10 feet,
unless you are dealing with very low voltage signals - check the
equipment specs - sometimes maximum cable runs are specified).
3) Coiling a cable can actually work against you, as by doing this you
essentially create an inductor, which is a first order lowpass filter.
Again, I doubt that a ten foot run of cable is significant, but an
inductor will attenuate high frequency signal content.
4) Do not ground to the hull. This is almost certain to create ground
loop issues. I presume that your electrical system negative (common) is
not tied to the hull? When you have shielded cables, tie the shield to
ground or electrical negative at the device - at one end only of the
cable. The hull may be used as a safety / chassis ground for
components, but should not be considered a source of constant potential
to tie electrical commons to, including cable shields.
-Sean
PS Take everything I write as speculation - my background is mechanical,
not electrical.
Quoting "Smyth, Alec" <Alec.Smyth@compuware.com>:
> OK, I just went out to the sub and took a look. The cable has 9
> conductors and the penetrator is a 10 conductor, so I do have one
> available for a shield. Currently I've got a foot of standard wires
> coming out on the inside, wired to the cable that came with the sonar.
> That cable is coiled up, so I'm not sure the exact length, but would
> guess I probably have 10 feet inside and about the same outside. It
> would be hard if not impossible, for space reasons, to solder the
> original sonar cable to the penetrator directly, although it would be
> possible to greatly shorten the leads. The run from penetrator to
> instrument could be about 5 feet if I cut the cable. There appears to
> be no grounding of the original cable at either the transducer or
instrument end.
>
> What if I find external braid shielding, wrap the whole inboard cable
> assmbly in that (including the one foot of plain wires), and ground to
the hull?
>
>
> thanks
>
> Alec
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