Two GPS modules come up repeatedly for this kind of project: the NEO-6M and the NEO-M8N. Both are u-blox consumer modules with a ceramic patch antenna, but they differ in sensitivity, update flexibility, and price. The beacon uses NEO-6M by default because it is good enough and inexpensive.

Which one is right depends on your budget, your sky conditions, and how much you care about acquisition time and cold starts.

NEO-6M

The NEO-6M is the older, lower-cost module. Relevant properties:

Built-in ceramic patch antenna.
Default 9600 baud, 1 Hz update.
Adequate sensitivity for open sky.
Slower acquisition in some conditions than newer modules.
Widely available and cheap.

For a beacon that transmits position as a compact Morse coordinate, NEO-6M is sufficient. The coordinate is truncated to degrees and minutes anyway, so sub-meter precision is not required.

NEO-M8N

The NEO-M8N is the newer module. Relevant properties:

Better sensitivity and faster time-to-first-fix in many conditions.
More configurable update rate and navigation settings.
Usually more expensive.
Better performance under marginal sky.

If you operate in places where you only occasionally get a clean sky view, the M8N can help. It can acquire faster and hold a fix better when the view is partially obstructed.

Trade-offs

Aspect	NEO-6M	NEO-M8N
Price	Lower	Higher
Sensitivity	Adequate	Better
Cold start	Slower in marginal sky	Faster in many conditions
Configurability	Basic	More options
Suitability for this beacon	Good	Better, at higher cost

What Matters for the Beacon

For this beacon, the important factors are:

Ability to get a fix in open sky.
Ability to keep a fix when the device is deployed outdoors.
Price and availability.

The beacon does not need survey-grade position. It needs a usable fix often enough to include a coordinate in the payload when the user wants it. NEO-6M meets that bar in most open-sky deployments. NEO-M8N is the upgrade if you need better performance in marginal conditions.

Antenna Considerations

Both modules commonly ship with the ceramic patch on the board. The patch is the limiting factor more often than the chip inside. A better module with the same patch antenna gain will not magically outperform a worse module in a poor location.

If you need real improvement, improve the antenna environment: open sky, no metal above the patch, and a clear view upward. An external active antenna with an SMA feed is the next step beyond a better module.

Which to Buy

Buy NEO-6M if:

You want the cheapest working setup.
You will deploy in open sky most of the time.
You are okay with slower acquisition in some cases.

Buy NEO-M8N if:

You need better acquisition or hold in marginal sky.
You can pay more.
You want a more capable module for future projects.

Either works with the beacon. The firmware does not depend on the exact module as long as it speaks the standard NMEA the firmware expects.

NEO-6M GPS Module — wiring and parsing for the default module.
GPS Module Variants — the broader module landscape.
GPS Troubleshooting — fixing common GPS problems.

NEO-6M vs NEO-M8N