How to output GPS signal to a DSC radio?

[sdowney717]

Originally Posted by Tupaia

You are asking software engineers to fit lightbulbs what you have is a hardware issue.

The solution to your hardware problem is here.

Connect your GPS to your VHF radio | The Ensign magazine

Funny, I had seen that page before you linked it. It worked for him, so you know it can work, but he left out the details. Typical engineer, no instructions for someone else to make it work, you have to be an electrical engineer yourself to understand how. No parts list, no circuit diagram.

I already bought the 12v gps, and pretty sure it will connect to the vhf.

[CarinaPDX]

There are lots of ways to solve this, but the easiest is to buy an NMEA GPS puck for the radio - which also gives you a backup source. Most require 5VDC power, but some have voltage regulators for 12VDC. Otherwise use a 12VDC>5VDC converter for about $3. Hook the power input to the same breaker as the radio. Simple and done quickly. If you want links to such devices just ask.

If you insist on making it more complicated I can help, but why? So you can waste a lot of time to get a more complicated and less robust system with a single point of failure - the GPS puck.

Greg

[StumpLifter]

Originally Posted by rgleason

There is another way to do this.
Use an old gps puck, determine the power wires and provide 5vdc, then determine which wire is nmea in on your radio and connect that to what you think is nmea out on the puck. If that does not work, switch the two nmea puck wires.

This gives your DSC radio a dedicated gps that is not dependent on any other equipment.

Definitely the way I would go. Lowest cost. Most reliable. Lowest Power demand to maintain DSC. Easiest to upgrade if you find a better puck/GPS receiver in the future. No interface to monkey with when you power up your radio. Wiring Not a risky deal. Just test the different wire connections combinations til it works. You can place the puck outside for better reception while keeping the Radio in the cabin out of the weather.

[sdowney717]

WELL, its lousy GPS, not good.
Sometimes data appears in radio, mostly it does not appear.
Turn on radio, rarely comes in 1 second
Sometimes 45 seconds.
Once 1.5 minutes.
Most of the time, no data appears in radio.

https://photos.app.goo.gl/HPBHjJF4YMqhDsRY7

I posted a long video that shows it.
At least I know my wiring works.
But now I am GPS shy, dont want to throw out good money for stuff that has problems. I have no idea what GPS I can buy that is going to work like it should.

Does anyone know why its doing this?
I contacted the seller. opened a dispute.

[GILow]

Originally Posted by sdowney717

WELL, its lousy GPS, not good.
Sometimes data appears in radio, mostly it does not appear.
Turn on radio, rarely comes in 1 second
Sometimes 45 seconds.
Once 1.5 minutes.
Most of the time, no data appears in radio.

https://photos.app.goo.gl/HPBHjJF4YMqhDsRY7

I posted a long video that shows it.
At least I know my wiring works.
But now I am GPS shy, dont want to throw out good money for stuff that has problems. I have no idea what GPS I can buy that is going to work like it should.

Does anyone know why its doing this?
I contacted the seller. opened a dispute.

When you say sometimes data does not appear, do you mean even after, say, ten minutes?

Different GPS chips have different cold start times, and depending on the age of the device, that could be four or five minutes.

Also, what voltage is the radio supplying to the puck?

[CarinaPDX]

That should be a good GPS unit - TopGNSS is a big name. Unfortunately their documentation does not explain the two GND wires: I. would not assume that there is a good connection between them. So first short them together instead of the separate lines - easy to do and at least has a chance of success. [Edit: or test for resistance between the two GND lines.]

Cobra has chosen to provide zero documentation/specification for their interface, probably to sell their own GPS receiver. So I have to make some assumptions. The radio probably has an RS-422/485 interface (part of the NMEA 0183 2.0+ specification), and it is probably listening at 4800 baud (again, part of the spec). The GPS is putting out RS-232 at 4800, per the listing. 232 and 4522 are not the same thing, although they are close enough that they can usually inter-operate. My guess is that the radio's 422 serial IC is right on the edge of decoding the 232 signal. If so then the solution is simple and inexpensive: install an RS-232 to RS-422/485 converter, for under $10 from Amazon or eBay. This should make for a reliable connection if my diagnosis is correct. The adapters have male and female DB-9 connectors, so you will have to either wire up two DB-9 connectors to your rig, or get DB-9 break-out boards. Some of the converters come with one break-out board; I found one that had the pair, for $15: https://www.serialcomm.com/serial_rs...eral_info.aspx . Personally I would buy this one, assuming that tying the grounds together didn't work.

I have no other ideas, but the 232-422 mismatch does seem likely.

Greg

[Moo]

Originally Posted by sdowney717

WELL, its lousy GPS, not good.
Sometimes data appears in radio, mostly it does not appear.
Turn on radio, rarely comes in 1 second
Sometimes 45 seconds.
Once 1.5 minutes.
Most of the time, no data appears in radio.

https://photos.app.goo.gl/HPBHjJF4YMqhDsRY7

I posted a long video that shows it.
At least I know my wiring works.
But now I am GPS shy, dont want to throw out good money for stuff that has problems. I have no idea what GPS I can buy that is going to work like it should.

Does anyone know why its doing this?
I contacted the seller. opened a dispute.

Not being funny but are the rest of your connections as bad as those?



Got a link to the source of the GPS and the datasheet. Let's work through this. It could be the GPS but more likely something else.


Is the Baud rate of the GPS selectable? What is is set for and does it match the radio?


You have a fairly low end radio there too and I wouldn't rule that out as being the problem.



We have a few variables to work though here... but first the data sheet.


Edit... OK I read back a bit and found the link the unit you have. Can you tell us how you have set it up. The default baud rate looks like it is 9600 when it is set to NMEA?

[Reefmagnet]

I'd suggest a ground loop. This will pretty much result in the symptons you describe. The four wires connection makes me a little suspect, as the negative connection is typically commoned with one of the NMEA outputs. I had similar issues with a Uniden unit that never worked as per the published information and at the end of the day, I just (judiciously! [it might pay to temporarily insert a 1/8 A fuse inline while you try stuff out]) tried different wire combinations until it eventually fired up. And you don't need to wait while trying. Once you hit the jackpot the radio will instantly respond.

[Moo]

Originally Posted by Moo

Not being funny but are the rest of your connections as bad as those?



Got a link to the source of the GPS and the datasheet. Let's work through this. It could be the GPS but more likely something else.


Is the Baud rate of the GPS selectable? What is is set for and does it match the radio?


You have a fairly low end radio there too and I wouldn't rule that out as being the problem.



We have a few variables to work though here... but first the data sheet.


Edit... OK I read back a bit and found the link the unit you have. Can you tell us how you have set it up. The default baud rate looks like it is 9600 when it is set to NMEA?

Another look at the suppliers site shows that the PPS version of this device uses two black wires but the one in question should only use the one on pin 1. So the black wire from pin 1 of the GPS should go to black of the radio.. Looks like you have used the shield too. The shield should be connected to ground only at one end of the cable (to prevent ground loops) so disconnect the GPS and using your multi-meter check for continuity between shield and black. If there is continuity do not connect shield to anything at your joint. If there is no continuity connect shield and black together.

[CarinaPDX]

The fact that the radio intermittently displays the Lat/Lon means that the baud rate is correct. I suppose that the radio might autobaud but I doubt it - I haven't seen that in marine applications. Ground loop, or some other issue with the ground, is a definite possibility, which is why I recommended trying to tie the two grounds together. Even if it is a ground problem a proper 232-422 adapter should help, as RS-422 doesn't (directly) use the ground for the (-) signal; RS-422 uses differential input.

Greg

[Moo]

Originally Posted by CarinaPDX

The fact that the radio intermittently displays the Lat/Lon means that the baud rate is correct. I suppose that the radio might autobaud but I doubt it - I haven't seen that in marine applications. Ground loop, or some other issue with the ground, is a definite possibility, which is why I recommended trying to tie the two grounds together. Even if it is a ground problem a proper 232-422 adapter should help, as RS-422 doesn't (directly) use the ground for the (-) signal; RS-422 uses differential input.

Greg

No.. depending on the timing mismatched Baud rates will display intermittently.

[Reefmagnet]

Originally Posted by Moo

No.. depending on the timing mismatched Baud rates will display intermittently.

I'd be surprised if you'd get a whole nema sentence with asynchronous comms.

[CarinaPDX]

Originally Posted by Moo

No.. depending on the timing mismatched Baud rates will display intermittently.

No, not with a long string. And usually NMEA sentences end with an error-detection code. If you have ever connected a 9600 baud GPS to a 4800 baud input you will have seen garbage, if anything is displayed at all. It is very unlikely that baud rate is the issue.

Greg

[Moo]

Yes even then. I have connected just about every possibility. I cut my teeth on this stuff as telecoms engineer working in data comms back in the 1980s.

Anyway the OP needs to confirm that he has configured the unit to 4800 Baud and get rid of that extra black wire as a couple have mentioned and I detailed the test procedure for above.

[sdowney717]

Originally Posted by GILow

When you say sometimes data does not appear, do you mean even after, say, ten minutes?

Different GPS chips have different cold start times, and depending on the age of the device, that could be four or five minutes.

Also, what voltage is the radio supplying to the puck?

1.5 seconds is cold start time.
12vdc is the supplied voltage.
Even after 10 minutes nothing.
I have seen it work after a second, 45 seconds, 1.5 minutes or never at all.
GPS is being powered on as radio turns on.