Link budget
V/u transponder, telemetry beacon and command links
The links are computed for a 525 km orbit with a tumbling spacecraft and linear antennas. A fixed station closes every link with margin. A portable Yagi station works best above about 30° elevation, which matches the experience on earlier 1U linear-transponder missions.
Uplink (2 m)
145.875 MHz
representative, pending IARU
Downlink (70 cm)
435.775 MHz
representative, pending IARU
Per-user downlink
70 mW
350 mW transponder share ÷ 5 users
SSB end-to-end @10°
+6.3 dB
fixed station · portable -3.9 dB
Doppler (max)
±10.2 kHz
downlink · uplink ±3.4 kHz
Margin vs elevation
Link margin vs elevation
Telemetry (BPSK 1200) downlink and end-to-end SSB through the transponder (uplink and downlink combined)
Show data table
| Elevation (deg) | Telemetry - Portable (handheld Yagi) | SSB end-to-end - Portable (handheld Yagi) | Telemetry - Fixed (crossed Yagis + LNA) | SSB end-to-end - Fixed (crossed Yagis + LNA) |
|---|---|---|---|---|
| 5 | -2.2 | -5.7 | 8.1 | 4.6 |
| 10 | -0.5 | -3.9 | 9.8 | 6.3 |
| 15 | 1.1 | -2.3 | 11.4 | 7.9 |
| 20 | 2.5 | -0.9 | 12.8 | 9.3 |
| 25 | 3.8 | 0.3 | 14.0 | 10.6 |
| 30 | 4.9 | 1.4 | 15.1 | 11.7 |
| 35 | 5.8 | 2.3 | 16.1 | 12.6 |
| 40 | 6.6 | 3.2 | 16.9 | 13.4 |
| 45 | 7.3 | 3.9 | 17.6 | 14.1 |
| 50 | 8.0 | 4.5 | 18.2 | 14.7 |
| 55 | 8.5 | 5.0 | 18.7 | 15.2 |
| 60 | 8.9 | 5.4 | 19.1 | 15.7 |
| 65 | 9.2 | 5.8 | 19.5 | 16.0 |
| 70 | 9.5 | 6.1 | 19.8 | 16.3 |
| 75 | 9.8 | 6.3 | 20.0 | 16.6 |
| 80 | 9.9 | 6.4 | 20.2 | 16.7 |
| 85 | 10.0 | 6.5 | 20.3 | 16.8 |
| 90 | 10.0 | 6.6 | 20.3 | 16.8 |
Line-item budgets
Telemetry downlink (BPSK 1200) — Portable (handheld Yagi), 10° elevation
| Parameter | Value | Unit |
|---|---|---|
| Frequency | 435.775 | MHz |
| Spacecraft TX power | -10.0 | dBW (100 mW) |
| Spacecraft line loss | -1.0 | dB |
| Spacecraft antenna gain | -3.0 | dBi |
| EIRP | -14.0 | dBW |
| Slant range | 1756 | km |
| Free-space path loss | -150.1 | dB |
| Polarization loss | -3.0 | dB |
| Atmos./ionosphere | -0.5 | dB |
| Ground antenna gain | 7.5 | dBi |
| Ground line loss | -0.5 | dB |
| Ground system noise temp | 26.5 | dBK (450 K) |
| G/T | -19.5 | dB/K |
| C/N0 | 41.4 | dB-Hz |
| Data rate | 30.8 | dB-Hz (1200 bps) |
| Required Eb/N0 (incl. impl. loss) | 11.1 | dB |
| Link margin | -0.4 | dB ✗ below threshold |
Transponder downlink, per user (SSB) — Portable (handheld Yagi), 10° elevation
| Parameter | Value | Unit |
|---|---|---|
| Frequency | 435.775 | MHz |
| Spacecraft TX power | -11.5 | dBW (70 mW) |
| Spacecraft line loss | -1.0 | dB |
| Spacecraft antenna gain | -3.0 | dBi |
| EIRP | -15.5 | dBW |
| Slant range | 1756 | km |
| Free-space path loss | -150.1 | dB |
| Polarization loss | -3.0 | dB |
| Atmos./ionosphere | -0.5 | dB |
| Ground antenna gain | 7.5 | dBi |
| Ground line loss | -0.5 | dB |
| Ground system noise temp | 26.5 | dBK (450 K) |
| G/T | -19.5 | dB/K |
| C/N0 | 39.9 | dB-Hz |
| Noise bandwidth | 33.8 | dB-Hz (2400 Hz) |
| Required C/N | 10.0 | dB |
| Link margin | -3.9 | dB ✗ below threshold |
User uplink to transponder (SSB) — Portable (handheld Yagi), 10° elevation
| Parameter | Value | Unit |
|---|---|---|
| Frequency | 145.875 | MHz |
| Ground TX power | 7.0 | dBW (5 W) |
| Ground line loss | -0.5 | dB |
| Ground antenna gain | 5.0 | dBi |
| EIRP | 11.5 | dBW |
| Slant range | 1756 | km |
| Free-space path loss | -140.6 | dB |
| Polarization loss | -3.0 | dB |
| Atmos./ionosphere | -0.5 | dB |
| Spacecraft antenna gain | -3.0 | dBi |
| Spacecraft line loss | -1.0 | dB |
| Spacecraft system noise temp | 28.5 | dBK (700 K) |
| C/N0 | 63.5 | dB-Hz |
| Noise bandwidth | 33.8 | dB-Hz (2400 Hz) |
| Required C/N | 10.0 | dB |
| Link margin | 19.7 | dB ✓ ≥ 3 dB |
Command uplink (FSK) — AMSAT command station, 10° elevation
| Parameter | Value | Unit |
|---|---|---|
| Frequency | 145.875 | MHz |
| Ground TX power | 20.0 | dBW (100 W) |
| Ground line loss | -1.5 | dB |
| Ground antenna gain | 14.0 | dBi |
| EIRP | 32.5 | dBW |
| Slant range | 1756 | km |
| Free-space path loss | -140.6 | dB |
| Polarization loss | -3.0 | dB |
| Atmos./ionosphere | -0.5 | dB |
| Spacecraft antenna gain | -3.0 | dBi |
| Spacecraft line loss | -1.0 | dB |
| Spacecraft system noise temp | 28.5 | dBK (700 K) |
| C/N0 | 84.5 | dB-Hz |
| Data rate | 39.8 | dB-Hz (9600 bps) |
| Required Eb/N0 (incl. impl. loss) | 15.0 | dB |
| Link margin | 29.7 | dB ✓ ≥ 3 dB |
Ground station classes
| Station | Uplink (W) | 2 m gain (dBi) | 70 cm gain (dBi) | Downlink Tsys (K) |
|---|---|---|---|---|
| Portable (handheld Yagi) | 5 | 5.0 | 7.5 | 450 |
| Fixed (crossed Yagis + LNA) | 50 | 12.0 | 15.0 | 250 |
| AMSAT command station | 100 | 14.0 | 16.0 | 200 |
Assumptions
- Spacecraft RF (AMSAT LTM): 100 mW telemetry only, 450 mW telemetry plus transponder. The transponder's 350 mW is shared among 5 simultaneous SSB users.
- Spacecraft antennas: −3 dBi effective for a tumbling monopole or dipole (an allowance for pattern nulls) and 1 dB line loss. The 2 m element is TBD (see open items).
- Spacecraft receive noise: 700 K for an Earth-facing VHF antenna (about 290 K Earth plus man-made noise) and the LNA.
- Propagation: 3 dB polarization loss (linear spacecraft vs circular ground, or Faraday fading) and 0.5 dB atmospheric and ionospheric loss.
- Required SNR: 10 dB in 2.4 kHz for SSB, 6 dB in 500 Hz for CW. BPSK needs Eb/N0 of 9.6 dB (uncoded 10⁻⁵) plus 1.5 dB implementation loss. This is conservative; FoxTelem's FEC improves on it.
- Ground gains are typical amateur values (handheld 2 m / 70 cm Yagi, crossed Yagis with LNA) and have not been checked against vendor data.
Model source: analysis/link_budget.py.