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Simrad SimNet Noise Filter? |
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SimonGH 
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Joined: 08 September 2021 Location: CT Status: Offline Points: 77 |
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 Topic: Simrad SimNet Noise Filter?Posted: 14 June 2022 at 02:40 |
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Does anyone have the "Noise Filter" in the triple prong SimNet connector under the mast step? Mine looks like a regular terminator, the "noise filter" is supposed to also have a capacitor. Curious if anyone has this and what theirs looks like? I'm having an issue with my 508 wind sensor (new) where it doesn't come back to life after the power to the SimNet network is turned off. The only solution is to disconnect and reconnect it, where it then comes back to life. It's a brand new sensor replaced in the fall...  Edited by SimonGH - 15 June 2022 at 11:57 |
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Ian Coverdale
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Joined: 19 June 2019 Location: Northen Ireland Status: Offline Points: 141 |
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Posted: 14 June 2022 at 09:11 |
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Sorry your picture is not showing.
Should not need any kind of 'noise filter' in Simnet. Simnet is an industry standard CANBUS protocol that is very robust providing installation guidelines have been followed.
Are you sure this unit is not some kind of lightning protection? If so, they often contain components called varistors that degrade over time. Try unplugging it and see if your problem clears. Cheers. |
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Ian & Andrea
SV Gabrielle (H445) Bangor, Northern Ireland. |
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iemand
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Joined: 13 February 2004 Location: Germany Status: Offline Points: 1074 |
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Posted: 14 June 2022 at 11:06 |
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The purpose of that "Noise Filter" is in the end a termination of the bus. Normally on a Simnet the Windfane terminates the Bus on one side and the Power supply on the other end. When the windfane is not installed you need the "Noise Filter". If everything is fully installed than you don't need that.
Basically it is only a Resistor.
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Hanse 312 MJ 2004 - Hanse 370e MJ 2007
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Ian Coverdale
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Joined: 19 June 2019 Location: Northen Ireland Status: Offline Points: 141 |
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Posted: 14 June 2022 at 11:26 |
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Confusion with terminology. Resistor is 120-Ohms, purpose is to damped 'reflections' back along the cable. It is kind of noise I guess. CANBUS is fussy with terminations.
Sure the 508/608 has built in termination resistor; you do not need an extra termination resistor at mast base. It you connector multi-meter across SIMNET L/H, A/B or data+/- connection (whatever they call it in your system) with everything switched off, you should measure ~60-Ohms (two end termination resistors in parallel). If you measure ~40-Ohms them you have an extra termination resistor. If ~120-ohms then you are missing an end termination or there is a break in your SIMNET network. Cheers.
Edited by Ian Coverdale - 14 June 2022 at 11:27 |
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Ian & Andrea
SV Gabrielle (H445) Bangor, Northern Ireland. |
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Peter-Blake
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Joined: 04 March 2008 Status: Offline Points: 2464 |
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Posted: 14 June 2022 at 15:30 |
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I am wondering why newer boats still need a noise filter. My boat from 2008 has one under the mast. The reason was, that they used the wrong cable in the sparcraft mast, and we got strange readings from the windvane. Later boats should have the correct cable...... This is how my noise filter looks like:  |
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Blake 370
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Ian Coverdale
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Joined: 19 June 2019 Location: Northen Ireland Status: Offline Points: 141 |
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Posted: 14 June 2022 at 15:58 |
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Not come across this before .. SIMRAD did sell a noise filter (part number 24006934) but I cannot find any recent reference to it. Mentioned in NSE-8 manual; a 12-15 year old instrument which is about the age of your boat? Not mentioned in later manuals so suggest SIMRAD improved instrument immunity to 'noise'?
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Ian & Andrea
SV Gabrielle (H445) Bangor, Northern Ireland. |
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SimonGH
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Joined: 08 September 2021 Location: CT Status: Offline Points: 77 |
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Posted: 15 June 2022 at 11:59 |
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If you zoom in on the mast area diagram: 
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SimonGH
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Posted: 15 June 2022 at 12:02 |
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I believe it is supposed to be there.
Refer to this article in Panbo (ok, from 2011) In one of the comments: "I’ve been told it contains a 120 Ohm termination resistor as well as a 220 μF capacitor. So it is completely passive. It lowers total impedance to 120/3 = 40 Ohm instead of the standard 120/2 = 60 Ohm. Apparently it was cooked up by Simrad when Hanse started equipping 1000’s of sailing yachts with large(r) N2K networks, with the network cable going all the way up into the mast." |
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SimonGH
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Posted: 15 June 2022 at 12:03 |
Thanks Peter. Mine definitely doesn't look like that - that looks like the pictures i've found. Mine looks like a regular terminator. I believe the longer part is the capacitor. Mine looks like this:  Edited by SimonGH - 15 June 2022 at 12:07 |
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SimonGH
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Posted: 15 June 2022 at 12:11 |
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Ultimately the question is whether the absence of this item would cause the wind sensor not to "come alive" after the power has been turned off on the bus.
I've also got to check the voltages under the mast step in that 3-prong connector, as that may contribute to the issue as well. But the bottom line is that at least in this diagram, the total resistance across the H/L on the bus would actually measure 40 ohm, not 60 ohm, and that apparently was by design. Additionally there should be some capacitance as well. |
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Peter-Blake wrote: