The hardware, and what actually matters in it

Before spending anything, check that your meter transmits. Roughly one meter radio in three is not in the 902–928 MHz band at all, and no amount of good hardware fixes that.

Assuming it does transmit, here is the whole shopping list.

The dongle

Any receiver built on the RTL2832U demodulator with an R820T2 tuner will do this job. That describes most of the market: Nooelec NESDR Smart, RTL-SDR Blog V3, and a long tail of unbranded kits.

The one specification worth paying for is a TCXO — a temperature-compensated crystal oscillator. Bargain dongles use a plain crystal that sits somewhere between 30 and 100 ppm off frequency, and worse, moves as the dongle warms up. At 915 MHz, 100 ppm is about 91 kHz of error.

The V4 trap

The RTL-SDR Blog V4 is a good receiver and a bad default recommendation, because it does not use the R820T2 — it uses an R828D with a different tuning arrangement. It needs a librtlsdr build that knows about it. On an older distribution, the V4 will be detected, will appear to open, and will return noise or nothing at all, with no error message that points at the real cause.

If you buy a V4, install the driver from RTL-SDR Blog's own fork before concluding anything about your meter. If you would rather not think about it, buy a V3 or a Nooelec and the stock rtl-sdr package in any distribution will just work.

Running two dongles

Worth knowing early, because it changes what you buy: a common and genuinely useful layout is two dongles — one parked on your meter's frequency logging continuously, one sweeping the band looking for anything new.

Both dongles ship with the same serial number, 00000001, which means librtlsdr cannot tell them apart and your two services will fight over whichever enumerates first. Fix it once, permanently, before wiring anything up:

rtl_eeprom -d 0 -s 1000     # the watcher
rtl_eeprom -d 1 -s 2000     # the surveyor

Then address them by serial (-d serial=1000) in every service file rather than by index, and reboot order stops mattering.

The antenna

This is the decision that determines whether the project works. It is also the one that gets skipped, because dongles come in kits with an antenna in the box and it is natural to assume the included antenna is fit for purpose. It usually is not — the telescopic whips in cheap kits are cut for VHF/UHF television and are roughly four times too long for 915 MHz.

A quarter-wave at 915 MHz is 8.2 cm:

λ    = 300 / 915 MHz   = 32.8 cm
λ/4  = 32.8 / 4        =  8.2 cm

So: either buy a whip actually specified for 900–930 MHz — they exist for a few dollars, sold for LoRa and ISM telemetry — or collapse the telescopic whip in your kit down to 8.2 cm, which works surprisingly well against the kit's magnetic ground plane.

The cheapest possible proof: your meters' neighbours. Point the receiver at the band, run rtlamr -filterid= with no filter, and see whether anybody's meter appears. If half a dozen strangers' IDs scroll past, the antenna and receiver are good and the problem is elsewhere. If the screen stays empty in a residential neighbourhood, suspect the antenna long before you suspect the software.

The host

Anything with a USB port. A Raspberry Pi is the natural fit because this is a service you want running unattended for years, and a Pi's power draw makes that painless. A Pi Zero W is marginal — rtl_tcp plus a decoder at 2.4 MSPS is real CPU work — while any Pi 3 or later has ample headroom.

Two host-level details that cost real time:

• Get the dongle away from the computer. A Raspberry Pi is an unshielded digital board radiating broadband hash, and 900 MHz sits right in it. A $6 USB extension that moves the dongle 50 cm away and toward a window is the highest return-per-dollar purchase in this entire list — frequently a larger improvement than upgrading the dongle.
• Power matters. RTL dongles draw noticeably more than a typical USB device. On an underpowered supply you get intermittent USB resets that read as random decode failures.

What not to buy

• A HackRF, an SDRplay, or anything over $100. Meter traffic at 915 MHz is strong, unencrypted, and narrow. A $30 dongle is not the limiting factor and never will be. Spend the difference on the antenna.
• An LNA, at first. Meters within a hundred metres arrive plenty strong. An amplifier in a dense RF environment more often makes things worse by overloading the front end.
• A 900 MHz filter, at first. A SAW bandpass filter is genuinely useful if you are near a cell site or a paging transmitter and seeing intermodulation. Buy it as a fix for a problem you have measured, not as insurance.
• An upconverter or downconverter. Not needed. 915 MHz is comfortably inside the RTL2832U's native range.

Software

All free, all open source.

Start with rtl_433 in its promiscuous default mode for the first sweep. Once you know what protocol your meter speaks, switch to rtlamr filtered to your own meter ID and leave it running.