Simnet Noise Filter

Recently I became aware of the fact that (a) Simrad has switched to a new specification for their Simnet cabling and (b) that there is a "Simrad Noise Filter" that they recommend for installation in sailing boats.

As you can see here in an report from Ben @ Panbo on N2K cable mixing, Simnet cables used to contain a yellow/blue pair for the data wires. Apparently this type of cable caused issues as the impedance of a long stretch was not according to NMEA specifications. This naturally ends up giving problems when you have a IS 20 wind instrument at the other end of a 20m cable. In my case it's even worse as I had to order a 30m cable as my mast is 25m tall.

I've been told that Simrad has switched to a different cable that has white/blue data wires which has better characteristics. To 'fix' existing installations Simrad has also produced a "Simnet Noise Filter", P/N 24006934. The Simrad NSE documentation states on PDF page 32:

For a large systems or sailboats with a mast head wind sensor and long mast cable, it is recommended to use a SimNet noise filter (24006934). On sail boats the filter should be inserted at the mast junction. On larger systems without a mast head unit, the filter should be inserted centrally along the backbone.

The original 2006 era SimNet installation manual contains no reference to this. Probably these issues have become more prevalent with larger networks being deployed.

I've ordered such a noise filter. I've been told it contains a 120 Ohm termination resistor as well as a 220 μF capacitor to damp out supply issues. Once it gets delivered I'll report on what it contains and the effects on my network.

NMEA2000 support and DSC calls on a Simrad RS82/87

Yesterday I received an email query from someone who wanted to know whether a Simrad RS82 will put out the DSC Call Information, PGN 129808. As I had to visit the boat anyway I was able to run a small test by making an individual DSC call to my own VHF from someone else's RS82.

The good news is that making an individual DSC call is very simple, at least on a RS82, and I will definitely use this capability more often now that I have been reminded how simple it is.

The bad news is that, at least with the software version I've got in my RS82, it does not transmit the NMEA 2000 standard PGN but a Simrad specific PGN 130816. It is clearly a PGN that was defined early on in Simrad's Simnet/NMEA2000 adoption cycle as it is very much text based whereas all standard PGNs are all very much binary field based. This did make it very easy for me to add support for this PGN (although a few minor fields are still guesses on my part).

Here is an example of the PGN 130816 in action:

2010-09-14-16:53:05.600 3   9 255 130816 Simrad: Text Message:  Manufacturer Code = Simrad; Industry Code = 19; Product Code = 16393; A = 156; B = 1; C = 1; D = 7; SID = 1; Text = INDIVIDUAL CALL
2010-09-14-16:53:05.711 3   9 255 130816 Simrad: Text Message:  Manufacturer Code = Simrad; Industry Code = 19; Product Code = 16393; A = 92; B = 1; C = 1; D = 7; SID = 2; Text = RECEIVED FROM RS81/82
2010-09-14-16:53:05.805 3   9 255 130816 Simrad: Text Message:  Manufacturer Code = Simrad; Industry Code = 19; Product Code = 16393; A = 92; B = 1; C = 1; D = 7; SID = 3; Text = CALLER ID: 244087177
2010-09-14-16:53:05.879 3   9 255 130816 Simrad: Text Message:  Manufacturer Code = Simrad; Industry Code = 19; Product Code = 16393; A = 92; B = 1; C = 1; D = 7; SID = 4; Text = CATEGORY: INDIVIDUAL
2010-09-14-16:53:05.990 6   9  36  59904 ISO Request:  PGN = 60928
2010-09-14-16:53:05.994 3   9 255 130816 Simrad: Text Message:  Manufacturer Code = Simrad; Industry Code = 19; Product Code = 16393; A = 92; B = 1; C = 1; D = 7; SID = 5; Text = REPLY ON CHANNEL 77
2010-09-14-16:53:06.088 3   9 255 130816 Simrad: Text Message:  Manufacturer Code = Simrad; Industry Code = 19; Product Code = 16393; A = 84; B = 1; C = 1; D = 7; SID = 6; Prio = 1; Text = STOP ALARM: SELECT CHANNEL 77
2010-09-14-16:53:06.166 3   9 255 130816 Simrad: Text Message:  Manufacturer Code = Simrad; Industry Code = 19; Product Code = 16393; A = 84; B = 1; C = 1; D = 7; SID = 7; Prio = 2; Text = STOP ALARM

Note that the information in the call did not contain GPS position. Unfortunately I forgot to wait for the sending VHF to obtain a GPS position, so I have no idea what will be sent out when that does transmit a location.

If someone knows whether my guess at the 'Product Code' and 'Prio' fields are correct, and what the meaning of fields A, B, C and D is then please do tell.

And if you have a RS8x with newer software than me and are able to test DSC calls, or know whether its software can be updated know whether SW version 2.3 provides any updates in this area then I'm all ears.

The new packetlogger can be downloaded at the usual place.

Navico Broadband Radar (BR24) test

I've finally succeeded in capturing our new Simrad/Lowrance BR24 Broadband radar in screenshots that show what it can do in a way that can be understood without needing to know the local circumstances.

Here is a link to the Flickr set that shows them all.

The first picture shows the largest range that showed useful information. Our antenna was about 8 m up in the air. Still, it showed echos 10 to 15 nautical miles away. Mind you, these were large built up areas (small towns). The dikes themselves at 2-15 nm did not show up. Although not impressive, it does show that the range is there. Notice that there were a number of smaller sailing yachts (motor yachts don't tend to use this lake in F5-6 winds) but that these don't show up reliably at this range. In my experience, those do show up with a 'normal' magnetron based 4 KW radome radar. Also the coast and dikes would show up.

The second picture shows the close up detail that is very, very impressive! Going from immediately north to south-east of the center location you see a range of dots and echos stretching from the land shown on the chart into the water. This is a series of metal piles that large ships can moor up to when waiting for the lock. The echos stretching to the land are walkways so that people can load/unload.

To the W @180m to NW @100m you can see the echos of the buildings right on top of the gray building area shown on the chart.

Across the water you can see the mooring wall with the dike behind it. This is where BB shines with it's great range resolution and ability to separate objects behind other objects.

To the right is a Google Map view of the same area.

On all images you can see that man-made objects, in particular heavy or conductive matter such as metal, show up much better than the softer areas (earthen dikes, trees), especially further off.

If you have any questions regarding the objects or views that I have, please comment and I will expand this entry accordingly.

Tying it all together - Overview

{Updated: June 16, 2009}

Enough has been done now to show what the entire electrical and navigation system on Merrimac II is going to look like. The goal was to have a system that's easy to use but not clutter up the entire boat with displays at various places. Not that you'd guess this from the image shown here at right -- you'd better click on it to get a readable image if you want to see it in more detail!

The cabin/saloon will not have any displays, buttons or nav systems except for a radio and a TV (hidden in a cabinet) and a charging cradle for the iPod touch remote.

The doghouse will have a PC display and a chartplotter and nothing else; all complexity will be operable from the PC and the remote (iPod Touch).

Power

Let's start from basics: power supply. The electrons are going to come aboard as follows:

1. Solar panels. 6 x Sunware SPR-90. 90Wp per panel. These should keep her happy while we're not there -- and even for a large part when are! I estimate that they can supply up to 2 kWh per day.
2. High power Mastervolt 24V/75A alternator on the engine coupled with an Alpha charge regulator. I've purposely decided on this model, as it charges at higher amps when the engine is running slowly than it's larger brethren.
3. A Mastervolt Chargemaster 24V/30A charger.

This will be sunk into 6 x 225 Ah Mastervolt AGM batteries, connected as 3 x 2 to provide 24 V @ 675 Ah. This means we can use about 330 Ah == 8 kWh before we need to top up.

On the consumer side we'll have a Mastervolt DC/AC converter that generates 230V, and a DC/DC converter that provides 12V for the electronics. There will be no AC-AC path from the shore connection to anything on board. In this way we don't need a isolation transformer.

The AC side is used by the following:

1. Hydraulic power pump for the lifting keel.
2. Washing machine (Miele, with hot fill capability so it can use warm engine water.)
3. Dishwasher.
4. TV.

The 12 V bits are used for anything electronic that needs/wants this. This keeps the supply clean, even when we use heavy electrical engines like the anchor winch. All motors etc are to be kept off this circuit, obviously.

The 24 V bits are for everything else: lighting, fridge, freezer, winches, autopilot.

Network

The electronics are going to be running on three networks:

1. Ethernet
2. NMEA 2000
3. Masterbus

The Ethernet will interface the Wago Linux PLC, the "integrator" Linux computer that provides WiFi and cellular access, a navigation computer running Microsoft Windows, a HDS8 chartplotter and a Broadband Radar radome.

The NMEA 2000 data will carry all navigation data. The components on this network are: Simrad IS20 instruments, autopilot and AIS class B transceiver; Lowrance HDS8 chartplotter/fishfinder/radar.

The Masterbus will couple all Mastervolt chargers/converters to each other. It integrates to the Microsoft Windows PC using a Mastervolt USB interface and possibly to the Linux system usign a Modbus interface.

What's not yet entirely clear is what will be used to tie the NMEA 2000 and Masterbus to the PCs, and what the PCs will be like. I'm investigating whether I can interface to these buses using my own software and off the shelf or custom CAN bus interfaces, as both of them are actually CAN. The fallback scenario is to use a Simrad AT10 interface for the Nobeltec software, a CANUSB for snooping the NMEA 2000 data and a Mastervolt Modbus interface for snooping the Mastervolt data.

For the Linux PC I'm contemplating various systems, but at the moment it looks as if I might as well use two (almost) identical systems such as the fit-PC2 for both the "always on" server and the Windows navigation system. An alternative is to make the server something that is ARM or MIPS based, as that should use less power. Sourcing an ARM based computer that is frugal with power (e.g. 2-3 W in total), has Ethernet, Wireless and USB or even better CAN directly on board turns out to be harder than I thought. There are a good many suppliers, but most systems fail on either being able to support an uptodate Linux BSP, or have the wrong peripherals, or are very expensive, or have a lifetime that is too short. If that is the case I might just as well use an expendable x86 computer that has plenty of USB ports and low power.

Navigation data

There will be four displays in the cockpit: IS20 Wind, Graphic, Multi and an AP24 pilot control. This gives ample data at disposal. There will be two depth sensors: one on the hull and one at the bottom of the keel. This is not just for redundancy, but also to keep from having to perform mental arithmetic as the keel depth can be varied from 0,80 m (2.6 ft) to 3,15 m (10 ft). This is important as our home waters are very shallow. The sensors work at different frequencies so they should not interfere with each other. The HDS can switch its depth sensor off when it's not needed.

The doghouse will have two screens: a Lowrance HDS8 chartplotter that also shows depth-over-time (aka a Fishfinder) and Radar. Next to that will be a computer display running Nobeltec Admiral and various other software. It will also run MSCAN Meteo (for receiving weather and NAVTEX data) connected to an ICOM PCR1500 remote controlled SSB receiver. The doghouse will also contain a Simrad RS82 VHF as well as an ICOM portable VHF and a Simrad WR20 remote. The remote allows you to control all Simrad equipment remotely as well as use it as a Bluetooth "headset" for a cellphone.

Simrad/Lowrance NMEA2000 network power usage

Third in what is turning out to be a small series on power usage. This time I figured I'd benchmark the power usage of all the navigation equipment that I have collected so far for the new boat.

Again measured using a Voltcraft 3000 at the 230V AC, so the actual figures are too high by 10-20% when using a direct 12V DC source. Since I am going to use a 24 V to 12 V DC/DC converter that will probably have the same sort of efficiency as the AC/DC converter that I am using now, I figure these measurements are good enough for me personally.

Device	Power	Cumulative
Lowrance HDS-8 (backlight @ 6)	6.3W	6.3W
Simrad IS20 Wind wand	0.9W	7.2W
Airmar DST800 depth/speed/temp sensor	1.0W	8.3W
Lowrance EP-65R fluid level sensor	0.4W	8.7W
Navico NAIS-300 AIS-B (receive mode)	7.3W	16.0W
Simrad RC42 compass	0.9W	16.9W
Simrad IS20 Graphic display	0.8W	17.7W
Simrad IS20 Multi display	0.6W	18.3W
Simrad IS20 Wind display	1.0W	19.3W
Simrad AC42 course computer	2.5W	21.8W
Simrad AP24 auto pilot controller	0.8W	22.6W
Airmar P319 sonar (depth) sensor	1.4W	24.0W

As always there are some small surprises here:

1. The chartplotter only uses 25% of the power envelope
2. NMEA2000 nodes seem to use at least 0.4W.
3. The NAIS-300 uses more power than I'd thought it would. Being able to shut it down completely is something to be considered.

Note to self (and reader): this is on the benchtop, the following is still missing:

• RF300 rudder feedback (should be neglible)
• Hydraulic pump (e.g. using the autopilot as opposed to just having it in standby)
• VHF #1
• Simrad WR20 remote
• Broadband RADAR sensor
• Ethernet switch