Simple RF Tool

Computes load impedance and reflection coefficient from R/X or Γ, plots the point on a Smith chart, designs L-match and T-match matching networks for a target impedance, calculates transmission line electrical length and VSWR, converts between RF power/voltage units, and estimates fault distance from TDR (time-domain reflectometry) measurements.

Basic Parameters

Input Parameters
Positive = inductive, negative = capacitive
Enter R and X (or Γ) and click Calculate. The load point will be displayed on the Smith chart.
Smith Chart

L-match Matching Network

L-match Parameters
L-match Circuit
Click "Design L-match" to see circuit diagram
Impedance Transformation on Smith Chart
Impedance Points:
● Load - Load impedance ZL
● After 1st element - After series/parallel element
● Matched - Matched to Z₀
Trajectories (frequency sweep ±20%):
━━━ Trajectory: 1st element
━━━ Trajectory: Final
Adjust to see impedance at different frequencies
VSWR vs. Frequency

Transmission Line Transformation

Line Parameters
At load end (right side)
Positive = inductive
From Load → Generator
Direction:
● Load (right side)
● Generator (left side / input)
TwG (toward generator): Clockwise ↻
TwL (toward load): Counter-clockwise ↺
Transmission Line on Smith Chart

● Load (starting point) → ● Generator (input)
Rotation: Clockwise ↻ (TwG - toward generator)

T-match Matching Network

T-match Parameters
Higher Q = narrower bandwidth
T-match Circuit
Click "Design T-match" to see circuit diagram
Impedance Transformation on Smith Chart
Impedance Points:
● Load - Load impedance ZL
● After elem1 - After first series element
● After shunt1 - After first shunt element
● After shunt2 - After second shunt element
● Matched - Matched to Z₀
Trajectories (frequency sweep ±20%):
━━━ Trajectory: elem1 | ━━━ shunt1 | ━━━ shunt2 | ━━━ final
Adjust to see impedance at different frequencies
VSWR vs. Frequency

Power & Voltage Conversions

Power Conversions
Results
dBm 0.00
dBW -30.00
Watts (W) 1.000e-3
Milliwatts (mW) 1.000
Microwatts (μW) 1000.0
Nanowatts (nW) 1.000e+6
Voltage & Power Ratios
Note:
• Voltage ratio: dB = 20·log₁₀(V₂/V₁)
• Power ratio: dB = 10·log₁₀(P₂/P₁)
• +6 dB ≈ 2× voltage, 4× power
• +3 dB ≈ 1.41× voltage, 2× power
Common Power Reference Values
+30 dBm 1 W
+20 dBm 100 mW
+10 dBm 10 mW
0 dBm 1 mW
-10 dBm 100 μW
-20 dBm 10 μW
-30 dBm 1 μW

TDR - Time Domain Reflectometry

TDR Parameters
TDR step generator voltage
Internal impedance of TDR generator (typically Z₀)
Typical: RG58=0.66, RG213=0.66, Foam=0.80
Typical pulse rise time from generator
Distance to impedance mismatch
Impedance at fault/end (0 = short circuit, very high = open circuit)
Multiple reflections for realistic TDR behavior
TDR Principle:
Send a fast step pulse, measure reflections. Time delay reveals distance to fault, amplitude reveals impedance mismatch.
Time Domain Waveform

STEP-TDR simulation with multiple reflections and configurable source parameters.
Physics:
• Incident wave amplitude: Vinc = E × Z₀/(Zsource + Z₀) (voltage divider)
• For matched source (Zsource = Z₀): Vinc = E/2
• Reflected waves bounce between load (ρL) and source (ρS)
• Steady-state voltage: V∞ = E × Zload/(Zsource + Zload)
Examples (Zsource=Z₀=50Ω, E=1V):
• Open (ZL=∞): V → 1.0V | Matched (ZL=50Ω): V → 0.5V | Short (ZL=0): V → 0V
• High-Z (ZL=75Ω): V → 0.6V | Low-Z (ZL=25Ω): V → 0.33V

Measured Impedance vs. Distance

TDR-measured impedance as function of distance, calculated from voltage and current:
• Z(t) = V(t) / I(t) = Z₀ × V(t) / (2Vinc - V(t))
• Distance: d = (v × t) / 2
• Before reflection arrives: Z ≈ Z₀ (matched line)
• After reflection: Z changes to indicate fault impedance
• Shows what TDR instrument actually measures and displays

Smith Chart - Reflection Points

● Matched (Z₀) | ● Load/Fault impedance