If you’re a bit of a hardware hacker, this may be possible, but may not be easy. It’s possible the Trimble radio signal is a simple set frequency FSK serial signal, but they most likely have a frequency hoping system, and it may be very hard to receive it without trimble’s special hardware.
Unfortunately, the Reach RS+'s built in LoRa radio, sort of turns the serial data into packets instead of straight serial data, so the Reach LoRa radio built in doesn’t have much chance of reading it directly is not going to be able to read the trimble radio at all. But possibly it’s a simple single-frequency FSK system.
To investigate the trimble’s 900 mhz signal, pick up a cheap “software defined radio” that you can plug into your laptop, and read the radio signals. Download the FM modulated signal and look at it to verify it’s simple serial data, with start bit, stop bits, maybe parity/etc. You can find a cheap software defined radio to read the trimble signal here… for under $25.00, and the software is free on internet.
To then receive the Trimble, maybe you could try one of the cheap things used by FPV telemetry work, and you can search for 3dr and similar names on ebay, here’s an example.
Note you don’t need a transmitter with high power, the Trimble already has a high power transmitter that determines range. The receivers will all have similar sensitivity. But look for something that will work at the same frequency as the trimble is set to, and has simple serial output, TTL or RS232, often called UART, but not SPI or I2C or CAN, which often needs complex signals to set up and then will packetize the data. You may be best off finding an even simpler radio modem that is half-duplex (receives only) which could make things easier, but they tend to be more expensive, and setting baud rate may be difficult. The ideal radio modem would not have any flow control signals, no baud rate setting, just pass through the FSK signal to a digital demodulator, and output a TTL or RS232 level
serial data to your terminal.
A cheap and easy RS232 to TTL converter, you could power right off the Reach RS+ serial cable power output: https://www.sparkfun.com/products/11189
Again, if you’re a bit of an electronic buff, you could probably figure it out by purchasing about $50 worth of parts, and a Reach RS+ cable available on amazon or through emlid directly.
But start by picking up one of those software defined radios, and see if you can read the radio signal, verify you can get good clean digital serial data, and if so, you’re all set. $22.50 investment to try it out.
Post whatever you learn, so we know what you found out.