Can brand name gps receivers be used generically?

[Kropdad]

Hi, I recently purchased a Comar splitter and a nasa radar plotter and need a gps receiver to get it working and am after a cheapy to get it working. Its more of a fun project as a complete nav package is in the pipe works and I would like to play with this until then. There are brand name ones out there plus a vast amount of usb types but apparently usb types will not work so will brand name one work if I remove their plugs and just solder wires onto my unit? Also am I able to use the gps unit on a vhf radio at the same time?

[RaymondR]

What is the data connection requirement of the plotter. You can buy puck type GPS units with either USB or NMEA data outputs.

[Kropdad]

It has an nmea connection option.

[RaymondR]

Assuming it's NMEA 0183 you should be able to buy a puck type GPS with NMEA 0183 output and connect it. You may have to also provide a power supply as I believe the NMEA 0183 wiring scheme does not provide any power.

[CarinaPDX]

Often, but not always, the GPS interface on the plotter will have a small amount of output power to drive the GPS receiver. If we are going to do this "right" then please check the manual for the output connections. Look for "NMEA Vx.x", baud rate, RS-232, RS-422, voltage level (probably either 5V or 12V), and the connections available (RX, GND, +V, maybe RX-, etc). If there is power to be used from the plotter that allows the cleanest solution, otherwise source the power from the same breaker as the plotter, with 12V>5V converter if needed. I can help with selecting an inexpensive receiver if you can provide the i/f specs.

The other thing to consider: do you want a simple GPS receiver, or a multi-GNSS receiver? The latest can actively track up to three of the four GNSS constellations (GPS, GLONASS, BeiDou, Galileo). The newer modules are faster at getting a fix but the accuracy improvement is very small. The main value for having two or more GNSS tracked is for backup, if one goes down (i.e. unlikely for either GPS or GLONASS). Keep in mind that a receiver must either come with your desired defaults or you have to be able to program it (non-trivial effort). Again, I can find an appropriate receiver if you can provide the specs.

If you can provide the plotter make/model then perhaps there is a manual on-line.

Greg

[Kropdad]

Hi Greg,
Thanks for responding responding. The radar is an older NASA type and the splitter is a Comar ASR100. I have the wiring diagram and both use separate 12v and the radar has an nmea output that has black and red go to a buzzer with blue spare and I assume is where God signal goes. I have found YouTube how to do but can only source us types or brand name knock offs with propriety wiring. Can a GPS receiver work on different equipment or do they require one each?

[CarinaPDX]

I'm pressed for time at the moment, so can continue tomorrow. A GPS receiver that outputs NMEA standard signals can handle multiple listeners. Sometimes older units are meant for use with just a low noise amplifier and antenna, but they typically have coax and a BNC connector so probably not for you. Otherwise it will be a digital input, but the voltages, baud rate, and sometimes the sentences (encodings) vary so that info is needed for any GPS in order to match up. A would really like to see the wiring diagram - take a photo with your cell phone and attach it here.

Greg

[mlydon]

You can get a ‘chip’ gps for about $40 that will output nmea 0813 such as this:

https://www.adafruit.com/product/746

I took a similar one, powered it with the guts from a cheap cigarette lighter USB plug, put the whole package in a prescription bottle, and wired it to my last vhf, so the radio had a dedicated GPS receiver and wouldn’t complain at me if I wasn’t running my chart plotter. (The ones with dsc do that)

On the expensive side, I installed a vesper 8000 transponder on my new boat - it has a gps built in, with nmea 0813 output in addition to nmea2000. I again feed my vhf from that for the same reason.

Matt

[CarinaPDX]

IIRC NASA had a product they called "radar" but was not really radar. If you could give me more information perhaps I can find the manual online (their website has a page of links to manuals). My guess is that a GPS (only) receiver could be had for around $10 that would do the trick, we just need the specs - most importantly the baud rate. I would guess 4800 but since you won't be able to reprogram it we need to get it right.

@mlydon: that module is nice but similar can be had direct from China for around $10 (with a pigtail instead of PCB for under $8). It will be interesting to see how the tariffs are going to affect the direct business.

Greg

[Kropdad]

Hi Greg, from my research it appears to be NMEA 0183 with the slower rate of 4800.

[Kropdad]

https://www.google.com/url?sa=t&sour...=1568063326813

[CarinaPDX]

Yes, pretty simple. One key is that it requires 2V swings minimum, so a TTL level (3.3V or 5V) output from the GPS will work - which is much easier to find than RS-232 voltage levels. Also, it is the old unbalanced input, again most common. The NMEA standard is for 4800 baud (only, except for HS which is 38,400) and barring any other comment that is the way to bet.

The next question is whether you want GPS-only, GPS+GLONASS, GPS+GLONASS+BeiDou, or GPS+GLONASS+BeiDou+Galileo. I think there is some advantage to the GPS+GLONASS, just in case one system is down; some have reported good results for BeiDou in Asia, but it is probably not worth even a few dollars to go further. If you wanted a USB version to work with a computer I might recommend differently, but since you will have no way to change the programming it doesn't make sense. Having multiple constellations doesn't have much if any effect on accuracy.

Do you want an antenna for exterior mount? There are low-profile pucks, mushrooms that screw into an antenna mount, or just an open assembly for indoor only - your choice.

I'll give you some links once I get the answer. For OZ the best thing is to just order from Aliexpress.

Greg

[Kropdad]

Two option close to me https://www.ebay.com.au/itm/BU-353-S...-/221057093602 or https://www.ebay.com.au/itm/BU-353-S...-/221057093602

[Kropdad]

https://www.ebay.com.au/itm/Marine-F...4-2135a9bd7d22

[sdowney717]

https://www.aliexpress.com/snapshot/...Id=32917574949

Here is a marine one. $17
This is 12vdc, the black shield wire you leave unconnected, it is electrically the same as the small black wire. You crimp a terminal on it and secure the cable with a screw for extra yanking support.