Sovereign Access
Ground Receive Hardware ยท RTL-SDR + UHF Antenna ยท $1/month
Technical Overview
Sovereign Access is the cheapest way onto the network: ground-side receive hardware you can build or buy today, paired with a $1/month subscription that activates once a Sentinel Collective satellite is on orbit. There is no exotic engineering here โ it is the same receive chain documented in our ground station blueprint (hardware/blueprints/ground_station_blueprint.md), stripped to its minimum: a USB software-defined radio dongle and a UHF antenna tuned to 437.525 MHz, no transmit hardware, no rotator.
Subsystem Blueprints
SDR Receiver
- ยทRTL2832U + R820T2/R828D tuner dongle
- ยทTypical sensitivity โ โ120 dBm class
- ยท24โ1766 MHz tuning range (model-dependent)
- ยทUp to 3.2 MSPS over USB
- ยทOptional inline LNA + 430โ440 MHz SAW filter for range
Our verified reference part is the RTL-SDR Blog V4 ($40, 0.5 ppm TCXO) โ the same part in our full ground station bill of materials. A generic RTL2832U-based dongle (commonly $15โ25) will receive the 437.525 MHz downlink but without the temperature-stable oscillator, meaning more manual frequency correction during a pass. An optional LNA4ALL low-noise amplifier ($35, 0.5 dB noise figure) and 430โ440 MHz band-pass filter ($18) extend usable range in RF-noisy environments.
Antenna
- ยทTuned to 437.525 MHz
- ยทHalf-wave dipole reference design: 160 mm per arm
- ยทOr: 5-element Yagi (8.0 dBd) for directional range
- ยทSMA or N-type connector to dongle
The simplest build is a half-wave dipole cut to the same 160 mm arm length used on the satellite's own deployable antenna (ฮป/4 at 437.525 MHz โ 159.6 mm, adjusted for end effect). For serious range, our ground station BOM specs an Arrow Antenna 440-5S 5-element Yagi ($80, 8.0 dBd gain) on a mast โ well beyond what a $15โ40 entry kit needs, but available if you want to track passes near the horizon.
Decode Software (free)
- ยทrtl_fm โ FM demodulation, 9600 baud
- ยทDirewolf โ AX.25 TNC / packet decode
- ยทGPredict โ pass prediction from current TLE
- ยทOpen-source; runs on Linux, macOS, Windows, or a Raspberry Pi
The same decode pipeline documented for our full ground station: RTL-SDR โ rtl_fm (FM demod) โ Direwolf (AX.25 TNC) โ message/telemetry output. No proprietary software or company-hosted decoder is required to receive a pass โ you can verify the link yourself with public tools before any satellite is even on orbit, using known beacons like NOAA weather satellites at 162.550 MHz as a calibration reference.
Bill of Materials
| PART | SPEC | SUPPLIER | LOCATION | EST. |
|---|---|---|---|---|
| RTL-SDR Blog V4 dongle (verified ref. part) | R828D tuner, 0.5 ppm TCXO | rtl-sdr.com | Online retail | $40 |
| Generic RTL2832U dongle (budget option) | R820T2 tuner, standard crystal | Amazon / eBay | Online retail | $15โ25 |
| RTL-SDR Bias Tee v3 (optional) | Powers inline LNA from USB | rtl-sdr.com | Online retail | $10 |
| LNA4ALL low-noise amp (optional) | 0.5 dB NF, bias-tee powered | LNA4ALL.com | Online retail | $35 |
| 430โ440 MHz SAW filter (optional) | Mini-Circuits SBP-435+ | minicircuits.com | Online retail | $18 |
| UHF dipole or whip antenna | 160 mm arms, tuned to 437.525 MHz | Self-build or any UHF ham antenna | โ | $10โ80 |
Assembly & Build Sequence
The RTL-SDR Blog V4 is our verified reference part; a generic RTL2832U dongle works for casual reception at lower cost.
Simplest option: a half-wave dipole, 160 mm per arm, matched to 50ฮฉ with a small L-network or 1:1 balun (same design as our satellite's deployable antenna โ see hardware/antenna/uhf_patch_437mhz.md). A commercial UHF Yagi extends range for low-elevation passes.
rtl_fm + Direwolf for AX.25 decode, GPredict for pass prediction โ open-source, matching our own ground station software stack.
Check oscillator drift against a known signal (NOAA APT weather satellites at 162.550 MHz are a reliable, always-on reference) and apply a PPM correction in rtl_fm if needed.
Load current TLEs into GPredict, point your antenna (or just listen omnidirectionally with a dipole), and watch for decoded AX.25 packets in Direwolf during the pass window.
The companion app surfaces message history, emergency beacon status, and account state. The SDR hardware above is what actually receives the satellite's RF downlink.
Receiving requires no license. Transmitting (uplink) on the 145.825 MHz amateur band requires at least a Technician-class FCC amateur radio license under Part 97.
What $1/Month Actually Buys
The hardware above is yours to build or buy today and works the moment any Sentinel 1U is on orbit transmitting on 437.525 MHz โ it requires nothing from us to function as a receiver. The $1/month is for app-layer service: message relay, beacon activation, and account access on the Sovereign network once a Sentinel Collective satellite is launched.
No Sentinel 1U has launched yet. Sovereign Access is intent registration today, not an active service โ see the pre-launch disclaimer below.
Regulatory note: like the Sentinel 1U downlink itself, the 437.525/145.825 MHz links currently sit under FCC Part 97, which restricts use to non-commercial, no-pecuniary-interest operation. A paid subscription service over these specific frequencies requires either FCC Experimental Authorization or a Part 25 commercial license โ both open items, not yet filed. See hardware/mission-ops/frequency_plan.md.