GPS - Feeding other equipment

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GPS - Feeding other equipment

Postby johnrobinson » Tue Oct 03, 2006 8:47 pm

My GPS is currenty serving a VHF radio (DSC function) and the computer (Maptech) . . . I'm planning to add a new Radar and SSB both of which would also like to receive a NEMA083 signal from the GPS. I recall reading that at some point a typical GPS (Furuno 036) runs out of signal strength to serve so many pieces of ancillary equipment and some sort of signal boosting device is needed. Is there any experince out there with this issue, is it real, and what has been your solution. Thanks, John Robinson, s/v Crossings
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Postby sv_bruadair » Wed Oct 04, 2006 4:14 am

Hi John,

Good topic, I hope my experience will help you with connecting your gps nmea signal to your equipment.

Yes, the nmea signal is a weak signal and at some point, if too many 'listeners' are connected, the signal will become degraded. The gps nmea output (talker) is usually strong enough to provide information to at least two 'listeners' and upwards of four listeners. The amount of listeners really is dependant on the talker's output strength. Since there really is no standard it's hard to tell for each piece of equipment. Depending on the output quality anything over three or four listeners will cause the nmea signal to become unreliable.

But there are a couple solutions. The first is a small electronic box called a nmea expander. It usually has one nmea input, the signal is then amplified and goes to four isolated output connections. They are very easy to install and typically draws less than 50ma. Nmea expanders usually also have an output that can be connected to a serial port connector and provide the nmea signal (in your case gps info) to your laptop. Great if you're running computer navigation software. In your particular case this seems to be an ideal solution. There are a variety of manufacturers, my favorite being Noland Engineering. They have always provided prompt and courteous customer and technical service. One of my former customers needed one unit replaced just a month past the warranty period, and they still covered it. To see a variety of nmea interface units, including expanders visit this web site http://www.navstore.com/nmea_devices.asp

Another nmea solution to bring up for others reading this is the opposite problem. Wanting to combine multiple nmea signals (talkers) to one listener. An example is my autopilot. My Navman autopilot system only has one nmea input. I wanted to have the nmea signal from my gps, my back up gps, my laptop and my wind instrument connected to the autopilot. Unfortunately nmea signals are not synchronized. This means the signals would pile up on each other at the input and be of no use. So my solution was a nmea multiplexer. A multiplexer takes up to four different nmea inputs, buffers them in to one output sentence (strong enough to drive four listners) and gets all the information to the autopilot. This is also great for my repeater down in the cabin as it provides information from the gps, wind, depth, and heading from the autopilot right at my nav station. my multiplexer also has a usb connector for computer connectivity.

I hope this helps. If you have any questions or need clarification let me know.

Damon
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Postby johnrobinson » Wed Oct 04, 2006 7:19 pm

Damon; Thanks . . . just the advice that I needed . . .John Robinson, s/v Crossings
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Postby johnrobinson » Wed Oct 04, 2006 7:59 pm

Damon; I looked at the website you suggested and as I suspected the story doesn't end there . . . at least not for an amateur like me . . . My GPS output is wired to a 9-pin serial cable (before USB was popular) and I recently bought a new laptop for the boat which only has USB ports . . . so to connect them I had to get a serial to USB adapter which makes for a "clumsy" installation. I see that the Expanders have RS422 and RS232 outputs . . . can either one be wired directly to a USB cable ?? Regards, JOhn Robinson, s/v Crossings
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Postby sv_bruadair » Wed Oct 04, 2006 8:35 pm

John,

before I answer your question I need some additional information. Can you tell me the make and model of your unit that is providing the gps signal, as well as the make and models of the equipment you want to send the gps signal to? Some units use a single wire for nmea while others (most) use two wires to transfer nmea. I want to see what you have and see what will make the best sense as far as wiring goes.

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Postby sv_bruadair » Wed Oct 04, 2006 8:48 pm

John,

just out of curiousity, where are you located?

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Postby johnrobinson » Thu Oct 05, 2006 4:11 pm

Damon; I'm located in Seattle . . . my "talker" is a Furuno GPS, GP31 or 36, I'm not sure . . .I'll get my manul and wiring diagram this weekend and send another post on Monday with the information that you ask for. Thanks for your interest in my problem. Regards, John Robinson, s/v Crossings
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Postby sv_bruadair » Thu Oct 05, 2006 4:52 pm

Hi John,

Okay, there a couple solutions. Of course the easiest being more expensive while the least expensive requires more wires and connections. Your Furuno GPS actually has two nmea outputs, one is a two wire output that can be hooked up to a variety of listeners while the second output is a three wire output. This third output can be used to feed a variety of listeners as well as a computer. This is where your serial connector is connected. The reason for three wires is the third wire allows nmea input from the computer to the gps unit, may not be necessary.

So here are some possibilities....


Option 1: Easy, least expensive, requires no additional equipment.
Connect nmea output 1 from the gps to the inputs on your vhf and ssb radios as well as your autopilot. Best to run the nmea output to a small terminal strip, then the terminal strip to your equipment's input. Keep the serial connector on the nmea output 2 of the gps and connect to your computer via a usb/serial adapter. This will allow the gps signal to be sent to the computer and any commands from the computer back to the gps (this may not be important to you).


Option 2: Easy, minimal cost, requires nmea multiplexer with usb conenctor.
Connect the nmea output 1 from the gps to input #1 on the multiplexer. Connect the nmea output of the multiplexer to the vhf, ssb and autopilot via a terminal strip (multiplexer can drive up to 4 units, have done up to 6). Connect a USB cable from the computer to the multiplexer. The nmea output #2 on the gps is not used. I like this option the best because it will leave you options in the future to add additional nmea talkers to your equipment, such as nmea signals from the depth sounder, wind instrument or a backup (handheld?) gps. The wind signal for example would then be tied into your autopilot and you can steer a set angle to the wind. If you pre-wire a handheld gps connection into one of the multiplexer inputs it will allow you to have a quick back up should your primary gps quit (happened to us once near New Orleans). Leaves you an option to add a repeater at the nav station to show all your info as well. This option allows you to grow. There are two choices in multiplexers. The one from Noland Engineering is more economical with four inputs, one output and a usb port. Will drive up to four listeners safely. The ShipModul multiplexer has four inputs, two outputs (up to 8 listeners) and a usb port. More expensive of course. This option does not allow the computer to talk to the gps, but this is usually not important to many people. It will, though, allow the computer to talk to the autopilot if you desire. Very easy installation.

There are also a variety of options which would include multiple pieces of equipement such as one multiplexer and one expander, but then that's additional wiring and becomes a pain in the butt. Before going this route I would get the Shipmodul multiplexer with two outputs. I'm also sure there are other options that I'm not thinking of that others could contribute.

If you go to page S-1 and S-2 of your owners manual you'll see the wiring diagrams showing two nmea outputs. Let me know if you have any questions. Would love to know what you end up doing.

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Postby johnrobinson » Wed Oct 11, 2006 9:43 pm

Damon; I have a feeling that I'm getting some very professional advice for free so please know that I am very gretefull. It seems that your second option with the ShipModule Multiplexer is what I should do. Am I correct that the multiplexer will also stregthen the GPS signal as it sends it to the other listeners (radar< VHF, SSB, etc.) as does an expander?

Thanks for your help . . . regards, John Robinson, s/v Crossings
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Postby sv_bruadair » Sat Oct 14, 2006 2:54 am

As a retired 'expert' I'm glad I can help. While I spent the winter in the SF bay area I had the good fortune of helping Bill and Lisa (HC43) with their little radio issue and Dino and Cathy (HC43) with their huge radar install and nav station rebuild (all for good food and and a warm berth, the best trade so far). I really have a passion for marine electronics and miss my business very much. I learned in Mexico that if I let other cruisers know my field then I will have business to fill each day. Unfortunatley I didn't know this would happen so while in mexico I actually worked more than I played. So now I keep a lid on it out here, but love to fly back to the states for the occasional job when someone needs help. As much as I love cruising it does help to break up the monotany.

Anyway, yes, the output of the multiplexer is strong enough and stable enough to run 4 listeners. Depending on the model you choose it may have two outputs, which then would run 8 listeners. I have had the multiplexer with the usb port from noland engineering in my boat for two years and it was great. Unfortunatley it stopped working due to a technicians error (let's not say names). It was replaced under warranty but since I was in a remote location it was easier for me to buy a replacement than ship the old one back at the time. The current one I have is a multiplexer from Shipmodul with the usb port, two outputs and it also is programable so I can filter out duplicate sentences. Very nice unit, very easy to install, and about twice the price of the one from Noland Engineering (of course).

Feel free to let me know if you have any questions, and thanks for the kind words.

Damon
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