[C38] Knott Transducer

Mon Jun 9 17:44:15 EDT 2008

I wouldn't splice a radar cable, but I don't think it would affect the
range resolution very much (the pulse width is typically about 90 radar
feet in width) until you get to the 4Kw and higher power radars.  But
the rise time of the cable needs to exceed 10MHz, which can be met with
connectors, but not typically splices.  Affecting rise time would cause
you to miss small targets completely.

Sounders are probably not affected by splicing the cable.  I think they
are much lower in frequency (typically hundreds of kilohertz vs 10 or
more Mhz for radar, so they can pass through splices easily.  Also they
are not typically affected by the internal cable delays (speed of light
vs speed of sound in water), so I think no problem.

Knotmeters are in the 10's of hertz (if that), so no problem with
frequency, and the signal is typically current, so as long as the
connection is sound, it should not be a problem.  However the temp gauge
would probably not work right, since these are typically low voltage,
low current devices, and leakage current (signal going through the cable
insulation to ground) may cause an offset in accuracy.  However most of
them can be adjusted (calibrated) to offset any such losses.

Regards,
Les H
On Mon, 2008-06-09 at 12:34 -0700, Phil Gay wrote:
> Regarding the issue of splicing, I don't think that splicing a knot
> transducer wire is an issue.  The wire is spliced when installed.  Splicing
> the depth sounder and radar cable, however, is a no-no since they are
> "tuned" to the sender or antenna.  The depth sounder and radar depend on the
> timing of reflected signal and a splice can alter the timing.
> 
> Electrical guys, correct me if I am wrong.
> 
> Phil Gay
> C38 049 Que Linda
> Everett, WA
> 
> -----Original Message-----
> From: listserve-bounces at catalina38.org
> [mailto:listserve-bounces at catalina38.org] On Behalf Of Duff, Russ (R.W.)
> Sent: Monday, June 09, 2008 12:28 PM
> To: larrypi at linkline.com; Catalina 38 Listserve
> Subject: Re: [C38] Knott Transducer
> 
> The transducers are made by Airmar.  I also bought a replacement on ebay.
> Sorry, but I can't give you an answer on splicing, but that sure would be a
> lot easier than having to run the new cable.
> 
> Sincerely,
> Russ Duff
> Catalina 38, Hull #112
> "AVANTURA"
> Lake Erie
> Grosse Ile, Michigan
> RDUFF AT VISTEON DOT COM
> AVANTURA AT COMCAST DOT NET
>  
> 
> -----Original Message-----
> From: listserve-bounces at catalina38.org
> [mailto:listserve-bounces at catalina38.org] On Behalf Of Larry Malmberg
> Sent: Monday, June 09, 2008 3:00 PM
> To: 'Catalina 38 Listserve'
> Subject: [C38] Knott Transducer
> 
> OK, now here is a new one, I'm just full of questions.  We have Raymarine
> ST-60 Instruments on board with a Edison binnacle, three instruments one of
> which is the knot meter and sea temperature and timers.  Out knot transducer
> (I think this is the right term, it's the thing that turns and has a magnet
> in it I think LOL) was getting fouled as they do with critters growing in
> it.  
> 
> I did a stupid thing and soaked it in Lime Away thinking that would get rid
> of those pesky critters growing inside, well not only did it clean the
> transducer it ate up part of the transducer and now of course is doesn't
> work.  Where can I find a replacement?  
> 
> Raymarine apparently doesn't support it any longer and IF I can find a
> replacement do I have to run the wire all the way back to the binnacle or
> can I do a splice? 
> 
> This stuff never ends, does it?  LOL  Ahhh, the joys of owning a 1981
> Catalina 38 but I love her. 
> 
> 
> 
> 
> 
> 
> Best regards,
> 
> Larry Malmberg-President
> 
> Larry Malmberg Investigations and Security, Inc.
> 505 North Arrowhead Avenue - Suite 510
> San Bernardino, CA 92401-1200
> 909-383-8565, 800-655-4549 Facsimile 909-383-8566
> PI 15211, PPO 112446
> 
> www.larrypi.com
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