GNSS Engineering Tools
GNSS Receiver Link Budget Calculator
Drop in your antenna gain, LNA gain and noise figure, coax run, and receiver NF — get the cascaded noise figure, signal level at the receiver, and live C/N₀ in dB-Hz with track / acquire / clean / excellent zones. Built for GNSS integrators sizing antenna + LNA + cable chains before locking a BOM.
Friis cascade · GPS L1 1575.42 MHz
Drag any slider and the C/N₀ recomputes live. The dominant noise contributor in the chain is highlighted with an amber dot — that's where an upgrade buys the biggest improvement. Maximum cable length is back-solved against a 40 dB-Hz clean-track target.
Incoming signal
GPS L1 C/A minimum guaranteed = -128 dBm (3 dBi antenna). Add ~2 dB for a 5 dBi antenna, ~4 dB for a 7 dBi antenna like the TDXL-CA341 choke ring.
Antenna LNA (built-in)
Main coax run
Total cable loss: 6.50 dB
Inline LNA + second coax
Receiver
C/N₀ at receiver
Clean tracking48.0dB-Hz
Invariant down the chain — gain amplifies signal and noise equally.
Cascade NF
2.00 dB
Friis (referred to antenna)
Signal at receiver
-84.5 dBm
Absolute level after gain / loss
Net chain gain
+39.5 dB
Sum of LNAs minus cable loss
Max cable for 40 dB-Hz
≥ 500 m
Same antenna / LNA / receiver, current cable type
Stage breakdown
- Antenna LNA+46.0 dBNF 2.0●
- Cable 1 (LMR-400)-6.5 dBNF 6.5
- Receiver+0.0 dBNF 4.0
Antenna LNA contributes the most cascaded noise — upgrade it first for the biggest improvement.
Cascade NF uses Friis (1944) with noise figures in dB and gains positive for amplifiers / negative for cables. Passive lossy stages have NF equal to their loss in dB. C/N₀ uses kT₀ at 290 K (-174 dBm/Hz) and is reported at the antenna output — invariant down the chain because gain amplifies signal and noise equally. Cable loss values are datasheet figures at L-band (≈ 1.575 GHz) for new cable; weathered runs typically add 0.5–1 dB/100 m.
When you'd reach for this
When you'd reach for this
Link budget shows up at the design stage of every GNSS deployment, and as soon as a working installation starts losing fixes. Each case below uses the same Friis cascade — the inputs change, the math doesn't.
CORS / base-station design
You have a 100+ metre cable run from the rooftop antenna to the receiver inside. Choose between LMR-400 / LMR-600 / LMR-900 by entering each and watching the C/N₀ — you'll usually find a 46 dB antenna LNA already covers far more loss than you need, and a cheaper cable buys back almost nothing.
Choosing antenna LNA gain
GNSource antennas ship with 30 dB, 36 dB, or 46 dB built-in LNA variants. The high-gain version isn't always worth it — for short runs the cascaded NF is dominated by the LNA NF itself, and extra gain just amplifies the noise floor at the same C/N₀. The dominant-stage hint tells you whether an LNA upgrade actually moves the needle.
UAV / SWaP-constrained platforms
On a drone the cable is short and the receiver is close. The link budget here pays attention to NF more than gain — that's why our LCA600 / LCA700 series prioritises sub-1.5 dB NF over headline gain numbers.
Adding an inline LNA
Cable losses above 10–15 dB start to dominate cascade NF. An inline LNA halfway down the run can recover the budget. Toggle the inline-LNA section to compare with / without — it's almost always worth it for runs over 150 m.
Troubleshooting a degraded fix
If field fixes are sporadic, the chain may have drifted into the track-only zone. Dial in actual measured cable length and watch C/N₀: if you're below 35 dB-Hz the issue is almost always cable degradation, a corroded connector, or undersized LNA — rarely the receiver itself.
Verifying a quote / BOM
Before signing off on a GNSS BOM, run the proposed antenna model, cable type, and length through the calculator. Anything that lands C/N₀ below 40 dB-Hz is at risk under rain attenuation or partial LOS obstruction — request a higher-gain antenna or thicker cable from the supplier.
FAQ
Frequently asked questions
What GNSS integrators most often ask about receiver link budgets and the math behind them.
Why is C/N₀ in dB-Hz, not just dB?
C/N₀ is carrier power divided by noise power spectral density (per Hz). Carrier is in dBm (or dBW), noise is in dBm/Hz, so the ratio carries units of Hz — written as dB-Hz. Don't confuse it with SNR (in dB), which is C/N over a specific bandwidth. C/N₀ is the more fundamental quantity for GNSS because it's bandwidth-independent.
Doesn't a bigger LNA gain mean more C/N₀?
Only up to a point. Gain after the first amplifier amplifies signal and noise equally — C/N₀ is invariant. What does help is putting a low-NF amplifier first (which is exactly why GNSource antennas have an internal LNA right at the element). Once the first stage gain is high enough to mask downstream NF, additional gain is wasted — see Friis: F_cascade = F_1 + (F_2-1)/G_1 + ...; after G_1 is ≈ 30 dB the F_2 term is already negligible.
What's a realistic C/N₀ for GPS L1?
A clean rooftop receiver should see 45–50 dB-Hz on the strongest in-view satellites and 35–45 dB-Hz on weaker ones. Indoor or partial-LOS conditions drop into the 20–35 dB-Hz range. Below 25 dB-Hz the receiver can't maintain track. Anything above 50 dB-Hz is excellent and usually requires a high-gain antenna with a clear sky view.
How accurate are the cable loss numbers?
Datasheet values are within ±5 % at L-band for new cable in a lab. In the field, weathered runs and aged connectors typically add 0.5–1 dB/100 m beyond the datasheet, and a corroded connector can add 1–2 dB on its own. If you're sizing a critical run, add a 2–3 dB margin on top of the calculator's result.
Where does the 'maximum cable length' come from?
It's a bisection back-solve against a 40 dB-Hz C/N₀ target (the boundary between 'acquire' and 'clean track' zones) using your current antenna, LNA, and receiver values. Holding everything else constant, the calculator finds the longest cable of your chosen type that still produces ≥ 40 dB-Hz. Change the cable type and the answer updates.
Why doesn't the calculator ask for antenna gain separately?
Antenna gain feeds directly into the 'signal at antenna output' slider — the value represents the signal level reaching the LNA after antenna gain has been applied. A higher-gain GNSource antenna (7 dBi TDXL-CA341 vs a generic 3 dBi patch) gives you ~4 dB more signal at the LNA, which translates to ~4 dB more C/N₀ all else equal. The default of -128 dBm is the GPS-IS-200 guaranteed minimum at a 3 dBi antenna.
Need an antenna + LNA combo that wins the budget?
GNSource antennas ship with integrated LNAs from 30 to 46 dB gain and ≤ 2 dB NF — sized to drive 100 m+ of LMR-400 with C/N₀ to spare. Tell us your cable length, platform, and accuracy requirement; we'll spec a model that exits the calculator in the clean / excellent zone.