.. tittel: Friis Transmission Equation
.. slug: rf-friis-overføring-ligning
.. dato: 2025-12-26 15:00:00 UTC
.. tags: nettverk, kalkulator, verktøy
.. kategori: Kalkulatorer
..lenke:
.. beskrivelse: Bruk Friis-overføringsligningen for å finne mottatt signaleffekt fra sendeeffekt, antenneforsterkning og banetap. Brukes for planlegging av RF-linkbudsjett.
.. type: tekst
<style>
    .calc-container {
        max-width: 900px;
        margin: 20px auto;
        padding: 20px;
    }

    .calc-header {
        margin-bottom: 30px;
        padding: 25px;
        background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
        border-radius: 12px;
        box-shadow: 0 4px 6px rgba(0,0,0,0.1);
        color: white;
    }

    .calc-header h2 {
        margin-top: 0;
        color: white;
        font-size: 28px;
        margin-bottom: 10px;
    }

    .calc-header p {
        margin: 10px 0;
        opacity: 0.95;
        font-size: 15px;
    }

    .form-section {
        margin-top: 20px;
    }

    .form-row {
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: 20px;
        margin-bottom: 20px;
    }

    .form-group {
        display: flex;
        flex-direction: column;
    }

    .form-group label {
        margin-bottom: 8px;
        font-weight: 600;
        color: white;
        font-size: 14px;
    }

    .form-group input,
    .form-group select {
        padding: 12px;
        font-size: 16px;
        border: 2px solid rgba(255,255,255,0.3);
        border-radius: 6px;
        font-family: 'Courier New', monospace;
        background: rgba(255,255,255,0.95);
        transition: all 0.3s ease;
    }

    .form-group input:focus,
    .form-group select:focus {
        outline: none;
        border-color: #4CAF50;
        background: white;
        box-shadow: 0 0 0 3px rgba(76, 175, 80, 0.1);
    }

    .button-group {
        margin-top: 20px;
        display: flex;
        justify-content: center;
    }

    .calc-button {
        padding: 14px 35px;
        font-size: 16px;
        background: #4CAF50;
        color: white;
        border: none;
        border-radius: 6px;
        cursor: pointer;
        font-weight: bold;
        transition: all 0.3s ease;
        box-shadow: 0 2px 4px rgba(0,0,0,0.2);
    }

    .calc-button:hover {
        background: #45a049;
        transform: translateY(-1px);
        box-shadow: 0 4px 8px rgba(0,0,0,0.3);
    }

    .calc-button:active {
        background: #3d8b40;
        transform: translateY(0);
    }

    .result-section {
        background: white;
        border: 1px solid #e0e0e0;
        border-radius: 8px;
        margin-bottom: 15px;
        overflow: hidden;
        box-shadow: 0 2px 4px rgba(0,0,0,0.05);
        transition: all 0.3s ease;
    }

    .result-section:hover {
        box-shadow: 0 4px 8px rgba(0,0,0,0.1);
    }

    .section-header {
        background: linear-gradient(135deg, #4CAF50 0%, #45a049 100%);
        color: white;
        padding: 15px 20px;
        display: flex;
        justify-content: space-between;
        align-items: center;
    }

    .section-header h3 {
        margin: 0;
        font-size: 18px;
        display: flex;
        align-items: center;
        gap: 10px;
    }

    .section-content {
        padding: 20px;
        background: #fafafa;
    }

    .data-row {
        display: flex;
        margin: 12px 0;
        padding: 10px;
        background: white;
        border-radius: 4px;
        border-left: 3px solid #4CAF50;
    }

    .data-label {
        font-weight: bold;
        color: #555;
        min-width: 180px;
        flex-shrink: 0;
    }

    .data-value {
        color: #333;
        font-family: 'Courier New', monospace;
        word-break: break-word;
    }

    .data-value.highlight {
        color: #4CAF50;
        font-weight: bold;
        font-size: 18px;
    }

    .info-section {
        margin-top: 30px;
        padding: 20px;
        background: white;
        border-radius: 8px;
        box-shadow: 0 2px 4px rgba(0,0,0,0.05);
        border-top: 3px solid #4CAF50;
        font-size: 14px;
        color: #666;
        line-height: 1.6;
    }

    .info-section h4 {
        color: #333;
        margin-top: 0;
        margin-bottom: 10px;
        font-size: 16px;
    }

    .info-section code {
        background: #f5f5f5;
        padding: 2px 6px;
        border-radius: 3px;
        font-family: 'Courier New', monospace;
        color: #d63384;
    }

    .help-text {
        margin-top: 15px;
        font-size: 13px;
        color: rgba(255,255,255,0.9);
        background: rgba(0,0,0,0.1);
        padding: 10px 15px;
        border-radius: 4px;
    }

    /* Responsive design */
    @media (max-width: 768px) {
        .form-row {
            grid-template-columns: 1fr;
            gap: 15px;
        }
    }
</style>
<div class="calc-container">
<div class="calc-header">
<h2>Friis Transmission Equation Calculator</h2>
<p>Beregn den mottatte effekten i en trådløs overføring ved å bruke Friis-overføringsligningen. Skriv inn frekvensen og avstanden for å bestemme banetapet for ledig plass og Fresnel-soneradius.</p>
<div class="form-section">
<div class="form-row">
<div class="form-group">
<label for="frequency">Hyppighet:</label>
<input autocomplete="off" id="frequency" type="text" value="2.4"/>
</div>
<div class="form-group">
<label for="freunit">Frekvensenhet:</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">Avstand:</label>
<input autocomplete="off" id="distance" type="text" value="1"/>
</div>
<div class="form-group">
<label for="unit">Avstandsenhet:</label>
<select id="unit">
<option value="feet">Miles</option>
<option value="meters">Kilometer</option>
</select>
</div>
</div>
<div class="button-group">
<button class="calc-button" onclick="fresnelZone()" type="button">Kalkulere</button>
</div>
</div>
<div class="help-text">
<strong>Note:</strong>Friis-overføringsligningen beregner effekten som mottas av en antenne under idealiserte forhold gitt en annen antenne et stykke unna som sender en kjent mengde strøm.</div>
</div>
<div class="result-section" id="resultsSection" style="display: none;">
<div class="section-header">
<h3><span>📡</span>Beregningsresultater</h3>
</div>
<div class="section-content">
<div class="data-row">
<div class="data-label">Fresnel soneradius:</div>
<div class="data-value highlight" id="fnr">-</div>
</div>
<div class="data-row">
<div class="data-label">Sentrumspunkt:</div>
<div class="data-value" id="center">-</div>
</div>
</div>
</div>
<div class="info-section">
<h4>Om Friis-overføringsligningen</h4>
<p>Friis-overføringsligningen relaterer kraften som mottas av en antenne til kraften som sendes av en annen antenne, atskilt med en viss avstand. Ligningen står for antenneforsterkning og bølgelengden til signalet.</p>
<p><strong>Formel:</strong></p>
<p><code>Pr / Pt = Gt × Gr × (λ / 4πR)²</code></p>
<p><strong>Hvor:</strong></p>
<ul style="margin: 10px 0; padding-left: 20px;">
<li><code>Pr</code>= Strøm på mottaksantennen</li>
<li><code>Pt</code>= Utgangseffekt fra sendeantenne</li>
<li><code>Gr</code>= Forsterkning av mottakerantennen</li>
<li><code>Gt</code>= Forsterkning av senderantennen</li>
<li><code>λ</code>= Bølgelengde</li>
<li><code>R</code>= Avstand mellom antenner</li>
</ul>
<p><strong>Fresnel-sone:</strong>Fresnel-sonen er et ellipseformet område mellom sender- og mottaksantennene. Denne kalkulatoren beregner radiusen ved midtpunktet, som er avgjørende for å avgjøre om hindringer vil forstyrre signalet.</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>