RF Calculators

Formula: λ = c × VF / f; θ = 360° × ℓ / λ; delay = ℓ / (c × VF). A target phase gives ℓ = θ × λ / 360°.

Example: At 100 MHz and VF = 0.66, a 1 m cable has 181.944° electrical length and 5.054 ns one-way delay.

Model: Uniform, nondispersive medium. Positive electrical length is shown as a negative phase delay. Half/quarter-wave dimensions are electrical lengths, not a finished antenna cutting specification.

Formula: f₀ = 1/(2π√LC). Worst-case minimum frequency uses maximum L and C; maximum frequency uses minimum L and C. Bandwidth estimate = f₀ / loaded Q.

Example: A 100 nH inductor needs 25.3303 pF for 100 MHz. With L ±5% and C ±2%, the frequency range is approximately 96.6285–103.639 MHz.

Model: Tolerance results are independent worst-case corners, not a statistical confidence interval. Loaded Q must be supplied. The LC reactance plot is not a filter transfer function; losses, loading, and self-resonance are excluded.

Formula: Xᴸ = 2πfL; Xᶜ = −1/(2πfC). With series loss: Z = ESR + jX; |Z| = √(ESR² + X²); phase = atan2(X, ESR); Q = |X| / ESR.

Example: An inductive reactance of +50 Ω at 100 MHz requires 79.5775 nH. With 0.5 Ω ESR, component Q is 100.

Model: ESR is treated as constant across the plotted decade. Real ESR, inductance, capacitance, and parasitics vary with frequency. This series-loss Q is a component estimate, not the loaded Q of an entire resonator.

Formula: |ΓL| = (VSWR − 1)/(VSWR + 1). With one-way power attenuation a = 10^(−loss/10), |Γin| = a|ΓL|. Load incident power = aPf; returned power at input = a²|ΓL|²Pf.

Example: For 2:1 load VSWR and 100 W forward power with no cable loss, the load accepts 88.8889 W and reflects 11.1111 W.

Model: Forward power is the incident traveling wave at the cable input, not net transmitter output. The source termination absorbs the return wave; source re-reflections are excluded. Matched cable loss assumes real Zc = reference Z₀. A better input VSWR after cable loss does not mean improved load matching or radiation efficiency.

Formula: P = Vrms² / R = Irms² × R; dBm = 10 log₁₀(P / 1 mW); dBW = dBm − 30. For a sine wave: Vpk = √2 Vrms and Vpp = 2√2 Vrms.

Example: A sine wave of 1 Vpp across 50 Ω is 0.353553 Vrms, 2.5 mW, and 3.9794 dBm.

Model: Conversions use actual voltage across the specified real load, not open-circuit generator voltage. Gain/loss is a matched power ratio with the same reference resistance. Compression, waveform crest factor changes, reactive loads, and mismatch are excluded.

Formula: Prx = Ptx + Gtx + Grx − Ltx − Lrx − Lother − FSPL. FSPL = 20 log₁₀(4πdf/c). Link margin = Prx − sensitivity; remaining margin = link margin − desired reserve. Midpoint first-Fresnel radius = √(λd)/2.

Example: At 2.4 GHz over 1 km, Ptx = 20 dBm, antenna gains = 2 dBi each, and feed losses = 1 dB each give Prx ≈ −78.052 dBm. Sensitivity −90 dBm leaves 11.948 dB margin, or 1.948 dB after a 10 dB reserve.

Model: Far-field free space, fixed user-entered gains/losses and sensitivity. Budget distance is not a coverage guarantee. Antenna dimensions, terrain, Earth curvature, diffraction, interference, weather, and fade statistics are not modeled. Fresnel values are geometric guidance, not a surveyed clearance check.