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Old 28-10-2009, 19:18   #1
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Cheap GPS Receiver for Icom VHF Radio

I have an Icom 500 series fixed mount VHF radio mounted at the NAV station. I have it wired to my 12 year old magellan GPS chartplotter to get position data but that doesn't work very well. Sometimes the radio displays question marks instead of the actual postiion (it does this intermittently, showing position for a second and then the question marks for a second) and recently it doesn't display position at all, perhaps a wire got loose. I'd much prefer to buy an additional GPS that I could mount right next to the Icom radio. Then I'd have a backup and an additional indicator of position.

Is there a cheap GPS that I can buy and install behind the overhead panel at the nav station without going through the trouble of installing and wiring another GPS antenna? The marine GPS receivers seem quite expensive. Instead I was thinking receivers sold for cars or computers would be cheaper. For example, Amazon is advertising a GlobalSat BU-353 USB receiver for $37 that one reviewer claimed could receive a signal through the deck. But this doesn't have the NMEA output I assume I'd need for the ICOM. Any suggestions?
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Old 28-10-2009, 19:30   #2
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Search for the USGlobalSat BR355. It is a serial output GPS puck, but with a PS2 connector and might do the trick for you. I've tried to order one from cheapGPS.com, but I wouldn't recomend them.
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Old 28-10-2009, 20:06   #3
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The BR355 seems to have gotten nice reviews. I found the pin layout at http://www.usglobalsat.com/download/57/br355_ds_ug.pdf. Would I connect the Icom to the TX pin and the ground pin? Also, it seems it works on 6Volts, which might be a problem. At least that's what the manual says for the PS2 connector. http://www.usglobalsat.com/download/...55_gps_win.pdf. I guess I'd need a convertor from 12V to 6V?
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Old 28-10-2009, 21:04   #4
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Why not try and fix the wiring first? The fix might be free!
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Old 29-10-2009, 05:26   #5
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For power, I was going to use an LM7805 (you can get them at Radio Shack). That little 3 pin device will take 12 volts and regulate it down to 5 volts with no other components needed. One pin to 12 v supply, one to your GPS puck, and one pin to negative. Or, you can get a car adapter for the Sirius satellite radio off Ebay. Those supply a regulated 5 volts. The hardest part might be finding a PS2 jack to plug it into if you aren't comfortable clipping off the connector to get to the wires.
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Old 30-10-2009, 19:26   #6
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Ok, I see the LM7805 on parts express online for $1. Looks like a three pronged chip. What should I mount this chip into? Is there some kind of small case made for it or were you just going to sodder wires directly onto it?
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Old 30-10-2009, 20:31   #7
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Ideally you would mount it to a larger piece of metal that would act as a heat sink. The heat sink tab on the LM7805 has a hole in it so you can use a small nut and bolt to attach it. You could also use some JB Weld epoxy to fix it to the heat sink, with or maybe without the nut/bolt. A thin layer of JB Weld does a pretty good job of transferring heat. The little plastic "project boxes" from Radio Shack come with an aluminum plate for use as the box's lid if you want. I would mount the LM7805 directly to that lid on the inside of the box, and run wires into the box and solder them to the device leads.
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Old 31-10-2009, 06:23   #8
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I wouldn't worry about a heat sink too much as the BR-355 only draws 80ma. With 12-14v input, the 7805 will be fine on it's own, however if you do go with the Radio Shack box as suggested, I would still mount it to the metal cover. You should always use a capacitor on both input and output terminals of the 7805. Some brands of the 7805 have been known to produce considerable RF hash without them. The 7805 is advertised as not requiring any external components and this is true as far as doing there job of providing a constant regulated output but it is always recommended to use these bypass capacitors as close to the regulator as possible to eliminate unwanted oscillation problems. PS/2 extension cables are available everywhere for a few bucks. You could just use one of those and cut the other end off to wire into your system. Then you don't need to cut the plug off the BR-355.

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Old 31-10-2009, 07:40   #9
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Thanks Eric. I was also thinking of getting the extension cord to leave the plug on. I thought I'd also buy the usb adapter for the BR-355 in case I needed to test it or configure it with a computer. The RF intereference sounds problematic as I was going to mount this right next to my VHF radio, as well as my stero and xm radio. Can you tell me which capacitors I need? Can I just sodder them to the ends of the 7805?

Also, this project seems to keep getting more complex. Does anyone know if this will work? Will it really receive a signal from inside the boat? Will the Icom radio be able to decipher the signal? For example the BR-355 says NMEA version 2.2, while the ICOM says it needs 2.0 or 3.01.
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Old 31-10-2009, 08:27   #10
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A couple of 0.1uF ceramic caps soldered directly to the leads should be fine in this situation. This GPS has the SiRF Star III chipset and should work just fine inside the boat and there should be no problem with the NMEA interface. The Icom should work fine with it.

Eric
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Old 02-11-2009, 13:53   #11
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the GlobalSat BU-353 USB does receive gps signal through the grp deck as i use it like that.
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