Advanced Calculator
Example Data Table
| Frequency MHz | Diameter m | Turns | Field | Unit | Angle | Inductance µH | Loss Ω | Load Ω | Use Case |
|---|---|---|---|---|---|---|---|---|---|
| 7.1 | 1.0 | 1 | 100 | µV/m | 0 | 15 | 2 | 50 | HF receiving loop |
| 14.2 | 0.8 | 2 | 250 | µV/m | 30 | 10 | 1.2 | 50 | Compact tuned loop |
| 3.5 | 1.5 | 3 | 80 | µV/m | 15 | 35 | 3 | 75 | Low band test loop |
Formula Used
The calculator treats the antenna as a small magnetic receiving loop. The wavelength is found from λ = c / f. Loop area is A = πr². The magnetic field is estimated from B = μ₀E / η. Here, η is free space impedance.
The open circuit voltage is Voc = 2πfNAB cosθ. This equation links frequency, turns, loop area, magnetic flux, and orientation. The small loop radiation resistance is estimated as Rr = 31200 × (NA / λ²)². Total series resistance adds conductor loss and radiation resistance.
Inductive reactance is XL = 2πfL. The tuning capacitor is C = 1 / ((2πf)²L). Thermal noise voltage uses Vn = √(4kTBR). The loaded voltage uses a voltage divider between loop resistance and receiver load.
How to Use This Calculator
Enter the operating frequency in MHz. Add the physical loop diameter in meters. Use the number of turns in the winding. Enter the incident electric field strength and choose its unit. Set the orientation angle. Zero degrees gives maximum magnetic coupling.
Enter loop inductance if you want resonance capacitance. Add conductor loss and receiver load resistance. Use bandwidth and noise temperature for noise checks. Press calculate. The result appears below the header and above the form. Use CSV or PDF buttons to save the output.
Receiving Loop Antenna Guide
Purpose
A receiving loop antenna senses magnetic flux from a radio wave. It is useful when space is limited. It is also helpful when noise direction matters. Many operators use loops for shortwave, medium wave, and direction finding. A loop can reject some electric field noise. This makes it attractive in crowded locations.
Main Inputs
The strongest inputs are frequency, loop area, turns, and field strength. Larger area produces more flux. More turns raise voltage. Higher frequency also increases induced voltage. Orientation matters because the loop responds to magnetic flux through its area. A broadside field gives the best response. A null appears when coupling falls near zero.
Advanced Results
This tool estimates voltage, resistance, resonance, noise, and antenna factor. Open circuit voltage is useful for sensor design. Loaded voltage is closer to receiver input voltage. Radiation resistance is usually very small for compact loops. Loss resistance can dominate performance. That is why copper loss and connection loss should be entered carefully.
Resonance Planning
A tuned receiving loop needs a capacitor across its inductance. The calculator estimates that value from frequency and inductance. This helps choose a variable capacitor range. A high Q loop can be selective. It can also become narrowband. Strong selectivity may help weak signal work. It may also require retuning when frequency changes.
Noise and Matching
The noise section uses thermal noise theory. It gives a basic voltage noise estimate. Real locations may have much higher atmospheric and man made noise. Matching is also important. A poor load can reduce delivered voltage. A preamplifier may help when loop voltage is low. However, it should not overload on strong nearby signals.
Practical Notes
Keep leads short. Use solid joints. Avoid lossy switches. Measure inductance if possible. The small loop check compares circumference with wavelength. If the loop is electrically large, the simplified model becomes less accurate. Use the result as an engineering estimate. Confirm final designs with measurement and field testing.
FAQs
What does a receiving loop antenna measure?
It mainly responds to the magnetic field component of a radio wave. The induced voltage depends on loop area, frequency, turns, field strength, and orientation.
Why is loop orientation important?
The loop voltage depends on magnetic flux through the loop area. Rotating the loop changes coupling. This can create useful peaks and nulls for reception.
What is the small loop condition?
A loop is usually considered small when its circumference is much less than the wavelength. This calculator flags the condition using circumference divided by wavelength.
Why is radiation resistance so small?
Compact receiving loops occupy a tiny fraction of a wavelength. Their radiation resistance can be very low, so conductor and connection losses often dominate.
What does tuning capacitance mean?
It is the capacitor value needed to resonate the entered loop inductance at the selected frequency. A resonant loop can provide higher voltage and selectivity.
Can this calculator design a transmitting loop?
It is intended for receiving analysis. Transmitting loops need current, voltage, heating, safety, and high power capacitor checks not included here.
Why enter receiver bandwidth?
Bandwidth affects thermal noise voltage. Wider bandwidth increases noise. Narrower bandwidth usually improves weak signal readability when the signal fits inside it.
Is the antenna factor exact?
No. It is an estimate based on the loaded voltage and incident field. Calibration, nearby objects, ground effects, and matching can change real values.