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I am thinking about a Rpi project that detects and triangulates radio signals with a directional Yagi Antenna, CMPS14 (to work out which compass direction the antenna is pointing) and a GPS to get current location.

The code will be written in Python.

Based on inputs from compass direction (CMPS14), signal strength (RTL-SDR), position (which GPS?) and a few fixes of the signal I should be able to locate the rough position of the signal.

The project at this stage is designed to me a man portable mobile unit, and is likely to be used a lot of the time under some tree cover and outdoors (cases will be needed with some level of waterproofing against rain).

I am looking at the various GPS options available for Rpi projects.

Give the tree cover situation it looks like a external antenna will be the way to go, with a GPS board that I connect to the Rpi. I also understand there are active and passive antenna's - which I presume will have some power implications - this is also a factor since the unit is likely to be battery powered and will want to run for a day or more at a time.

What is the difference between something like this:

http://www.efrontier.co.nz/estore/index.php?cPath=2_3

Versus something like Neo-M9N:

https://www.sparkfun.com/products/15712 (which I need to add a antenna to)

The Neo M9N seems to be referenced quite a bit on here as being a advanced GPS. I don't think I will need RTK, although a board that supports it might be fun to experiment with.

I think this provides enough information on the project to make some informed comments about which GPS components I should be looking at, but if further detail is needed please leave a comment.

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  • I used few of GPS modules but had best experience with USB white dongle from Ublox. You can even remove the plastic and access internal connections. Had great sensitivity and i did not have to hack anything, just plug and play. Dec 18, 2023 at 9:40

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The SparkFun (and similar) board can interface to the GPIO. I remember a bit of a learning curve when I did, but the nice part for me was the 1PPS output of the board works nicely with ntpd giving very accurate system time. The serial in/out on the breakout will communicate with the serial in/out on the GPIO. There's more work involved than a USB pluggable device. There's also gpsd which will use the output of the device and allow various client programs and utilities to read and write to the device, including the NMEA output.

I'm also working on both RTL-SDR receivers and direction finders on Raspberry Pi. Contact me if you'd like to know more about it. For direction finding we are using a FM receiver module for some applications also, which is easy to interface and requires less power than an RTL-SDR doing the same thing.

Amplitude of Arrival will certainly provide a rough estimate, but will be better outside of built-up areas, especially in flat terrain.

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  • Are you able to connect a CMPS14 and GPS via GPIO at the same time?
    – Al Grant
    Dec 17, 2023 at 18:01
  • I don't see why not. Both can use serial or I2C interfaces. As long as at least one is using I2C, the Pi will talk to them both. The I2C interface can support multiple simultaneous devices. (P.S. I sent you an email - if it didn't arrive, let me know).
    – Deepstop
    Dec 18, 2023 at 2:11

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