.. názov: Friis Transmission Equation
.. slimák: rf-friis-prenos-rovnica
.. dátum: 26. 12. 2025 15:00:00 UTC
.. tagy: networking, calculator, tool
.. kategória: Kalkulačky
.. odkaz:
.. popis: Použite Friisovu prenosovú rovnicu na nájdenie výkonu prijímaného signálu z vysielacieho výkonu, zisku antény a straty trasy. Používa sa na plánovanie rozpočtu spojenia RF.
.. typ: text
<style>
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        margin-top: 30px;
        padding: 20px;
        background: white;
        border-radius: 8px;
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        color: #333;
        margin-top: 0;
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    @media (max-width: 768px) {
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</style>
<div class="calc-container">
<div class="calc-header">
<h2>Friis kalkulačka prevodovej rovnice</h2>
<p>Vypočítajte prijímaný výkon pri bezdrôtovom prenose pomocou Friisovej prenosovej rovnice. Zadajte frekvenciu a vzdialenosť na určenie straty dráhy vo voľnom priestore a polomeru Fresnelovej zóny.</p>
<div class="form-section">
<div class="form-row">
<div class="form-group">
<label for="frequency">Frekvencia:</label>
<input autocomplete="off" id="frequency" type="text" value="2.4"/>
</div>
<div class="form-group">
<label for="freunit">Jednotka frekvencie:</label>
<select id="freunit">
<option value="ghz">Gigahertz (GHz)</option>
<option value="mhz">Megahertz (MHz)</option>
<option value="khz">kilohertz (kHz)</option>
<option value="hz">Hertz (Hz)</option>
</select>
</div>
</div>
<div class="form-row">
<div class="form-group">
<label for="distance">vzdialenosť:</label>
<input autocomplete="off" id="distance" type="text" value="1"/>
</div>
<div class="form-group">
<label for="unit">Jednotka vzdialenosti:</label>
<select id="unit">
<option value="feet">Miles</option>
<option value="meters">Kilometre</option>
</select>
</div>
</div>
<div class="button-group">
<button class="calc-button" onclick="fresnelZone()" type="button">Vypočítajte</button>
</div>
</div>
<div class="help-text">
<strong>Poznámka:</strong>Friisova prenosová rovnica vypočítava výkon prijímaný anténou za idealizovaných podmienok za predpokladu, že iná anténa v určitej vzdialenosti od seba prenáša známe množstvo výkonu.</div>
</div>
<div class="result-section" id="resultsSection" style="display: none;">
<div class="section-header">
<h3><span>📡</span>Výsledky výpočtu</h3>
</div>
<div class="section-content">
<div class="data-row">
<div class="data-label">Polomer Fresnelovej zóny:</div>
<div class="data-value highlight" id="fnr">-</div>
</div>
<div class="data-row">
<div class="data-label">Stredný bod:</div>
<div class="data-value" id="center">-</div>
</div>
</div>
</div>
<div class="info-section">
<h4>O Friisovej prevodovej rovnici</h4>
<p>Friisova prenosová rovnica dáva do súvislosti výkon prijímaný anténou s výkonom vysielaným inou anténou, oddelenými od seba v určitej vzdialenosti. Rovnica zohľadňuje zisky antény a vlnovú dĺžku signálu.</p>
<p><strong>Vzorec:</strong></p>
<p><code>Pr / Pt = Gt × Gr × (λ / 4πR)²</code></p>
<p><strong>kde:</strong></p>
<ul style="margin: 10px 0; padding-left: 20px;">
<li><code>Pr</code>= Napájanie na prijímacej anténe</li>
<li><code>Pt</code>= Výstupný výkon vysielacej antény</li>
<li><code>Gr</code>= zisk prijímacej antény</li>
<li><code>Gt</code>= zisk vysielacej antény</li>
<li><code>λ</code>= Vlnová dĺžka</li>
<li><code>R</code>= Vzdialenosť medzi anténami</li>
</ul>
<p><strong>Fresnelova zóna:</strong>Fresnelova zóna je elipsoidná oblasť medzi vysielacou a prijímacou anténou. Táto kalkulačka vypočítava polomer v stredovom bode, čo je rozhodujúce pre určenie, či prekážky budú rušiť signál.</p>
</div>
</div>
<script>
/**
 * Friis Transmission Equation Calculator
 * Calculates Fresnel zone radius based on frequency and distance
 *
 * Equation:
 * Pr / Pt = Gt × Gr × (Lambda / 4 × Pi × R)²
 *
 * Where:
 * - Pr: Power at the receiving antenna
 * - Pt: Output power of transmitting antenna
 * - Gr: Gain of the receiving antenna
 * - Gt: Gain of the transmitting antenna
 * - Lambda: Wavelength
 * - R: Distance between antennas
 *
 * Fresnel Zone Calculation:
 * For Miles: radius = 72.05 × √(d1 × d2 / f)
 * For Kilometers: radius = 17.32 × √(d1 × d2 / f)
 * Where d1 and d2 are distances from each antenna to the center point
 */

'use strict';

function fresnelZone() {
    // Get input values
    const frequency = Number(document.getElementById("frequency").value);
    const freunit = document.getElementById("freunit").value;
    const distance = Number(document.getElementById("distance").value);
    const unit = document.getElementById("unit").value;

    // Validate inputs
    if (isNaN(frequency) || frequency <= 0) {
        alert("Please enter a valid frequency greater than 0");
        return;
    }

    if (isNaN(distance) || distance <= 0) {
        alert("Please enter a valid distance greater than 0");
        return;
    }

    // Convert frequency to GHz
    let sf;
    if (freunit === "ghz") {
        sf = frequency;
    } else if (freunit === "mhz") {
        sf = frequency / 1000;
    } else if (freunit === "khz") {
        sf = frequency / 1000000;
    } else {
        sf = frequency / 1000000000;
    }

    // Calculate center point (halfway)
    const d1 = distance / 2;
    const d2 = d1;

    // Calculate Fresnel zone radius based on unit
    let radius, distunit;
    if (unit === "feet") {
        // For miles: radius in feet
        radius = Math.round(36.03 * Math.sqrt(distance / sf));
        distunit = "Miles";
    } else {
        // For kilometers: radius in meters
        radius = Math.round(8.657 * Math.sqrt(distance / sf));
        distunit = "Kilometers";
    }

    // Display results
    document.getElementById("fnr").innerHTML = radius + " feet";
    document.getElementById("center").innerHTML = "The center of the Fresnel Zone is " + d1 + " " + distunit + " from the first antenna.";

    // Show results section
    document.getElementById("resultsSection").style.display = "block";

    // Scroll to results
    document.getElementById("resultsSection").scrollIntoView({ behavior: 'smooth', block: 'start' });

    console.log(`Calculation complete: Frequency=${sf}GHz, Distance=${distance}${distunit}, Radius=${radius}ft`);
}

// Add enter key support for inputs
document.addEventListener('DOMContentLoaded', function() {
    console.log('Friis Transmission Equation Calculator initialized');

    // Allow Enter key to trigger calculation
    const inputs = document.querySelectorAll('#frequency, #distance');
    inputs.forEach(input => {
        input.addEventListener('keypress', function(e) {
            if (e.key === 'Enter') {
                fresnelZone();
            }
        });
    });

    // Auto-focus first input
    document.getElementById('frequency').focus();
});
</script>