GPS stand along device for Raymarine VHF radio?

[CarinaPDX]

Further to my previous post. The better GPS receivers frequently use uBlox GPS modules. The older uBlox 7 (typically part #7020) does not support Galileo, and IIRC can receive simultaneously two systems (GPS+GLONASS is typical). The newer uBlox 8 (typically #8030) can receive all four systems (GPS, GLONASS, Galileo, Beidu), up to three simultaneously (depending on combination). The module evaluates all of the satellites available on the chosen systems (GNSS), pares down the available to the best accuracy, then calculates a position. I have seen them evaluate GLONASS satellites but almost never use them - just not the same accuracy. For a multi-system receiver Galileo is the best alternative, but also the last to go live so many GPS modules don't support it (including early 8030 units). Nonetheless, having any other system provides useful redundancy.

From what I have been told, the modules can have some of their defaults changed by integrators (the ones that put the module in a product) by burning internal fuses. I believe this is how different baud rates and output modes can be customized. So if we order receivers that have the correct defaults for our application that is often how it is done. It is also possible to override defaults for a session, but that is lost upon shutdown. Some include flash storage for storing user defaults, which is highly desirable if you plan on customizing the settings. Also, some receivers with flash can have their firmware upgraded, which can be helpful.

The modules usually communicate with TTL voltage levels (0v to 3.3v-5v), and require a level shifter for RS-422 (-5v to +5v) communication. The modules operate on TTL levels for power input as well, so require a DC-DC converter for use on 12v. If a receiver doesn't say "12v" then it probably isn't.

As far as NMEA 0183 compatibility goes, do not assume that because it says "NMEA protocol" that it will work: they are referring to the "sentences" (GLL, GSA, GSV, etc), not the voltage levels. So check for "RS-232 level" (which is inaccurate, as 0183 uses RS-422, not the higher voltages of RS-232 - 15v, +15v) but that is what you need. Of course check that the sentences out and baud rate is what your radio needs.

If you are buying directly from an integrator (e.g. TopGNSS) it is often possible to have them program custom defaults for you. This would be useful for having GPS+Galileo as the default. Or possibly adding BeiDu as a third. I am not seeing a lot of GNSS receivers that have that as a default, and combined with the need for 12V power and NMEA 0183 compatibility that shrinks the market to a pretty small niche.

If it were me I would look at buying this direct from TopGNSS and ask them to set GPS and Galileo as the default GNSS (and maybe BeiDu if going to the Far East):
https://www.aliexpress.com/item/33032354629.html

If you are satisfied with GPS-only then maybe this:
https://www.aliexpress.com/item/32917574949.html .

Greg