.. titel: RF Fresnel Zone Calculator
.. snegl: rf-fresnel-zone
.. dato: 26-12-2025 15:00:00 UTC
.. tags: netværk, lommeregner, værktøj, RF, trådløs
.. kategori: Lommeregnere
.. link:
.. beskrivelse: Beregn Fresnel Zone-radius for trådløse RF-links for at sikre korrekt signaludbredelse
.. 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;
    }

    .input-grid {
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: 20px;
        margin-top: 20px;
    }

    .input-group {
        display: flex;
        flex-direction: column;
        gap: 8px;
    }

    .input-group label {
        font-weight: bold;
        font-size: 14px;
        color: rgba(255,255,255,0.95);
    }

    .input-row {
        display: flex;
        gap: 10px;
    }

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

    .input-group input {
        flex: 1;
    }

    .input-group select {
        min-width: 150px;
    }

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

    .calc-button {
        margin-top: 20px;
        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);
        width: 100%;
    }

    .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-top: 30px;
        overflow: hidden;
        box-shadow: 0 2px 4px rgba(0,0,0,0.05);
        display: none;
    }

    .result-section.show {
        display: block;
    }

    .section-header {
        background: linear-gradient(135deg, #4CAF50 0%, #45a049 100%);
        color: white;
        padding: 15px 20px;
        font-size: 18px;
        font-weight: bold;
    }

    .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: 220px;
        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-box {
        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;
    }

    .info-box h3 {
        margin-top: 0;
        color: #4CAF50;
        font-size: 20px;
    }

    .info-box p {
        line-height: 1.6;
        color: #555;
        margin: 10px 0;
    }

    /* Responsive design */
    @media (max-width: 768px) {
        .input-grid {
            grid-template-columns: 1fr;
        }

        .input-row {
            flex-direction: column;
        }

        .input-group select {
            width: 100%;
        }

        .data-row {
            flex-direction: column;
        }

        .data-label {
            margin-bottom: 5px;
            min-width: auto;
        }
    }
</style>
<div class="calc-container">
<div class="calc-header">
<h2>RF Fresnel Zone Lommeregner</h2>
<p>Beregn Fresnel-zonens radius for trådløse RF-links. Fresnel-zonen er et elliptisk område omkring den visuelle synslinje, som radiobølger spredes ud i efter at have forladt antennen.</p>
<div class="input-grid">
<div class="input-group">
<label for="frequency">Frekvens:</label>
<div class="input-row">
<input id="frequency" placeholder="Enter frequency" type="text" value="2.4"/>
<select id="freunit">
<option value="ghz">GHz</option>
<option value="mhz">MHz</option>
<option value="khz">KHz</option>
<option value="hz">Hz</option>
</select>
</div>
</div>
<div class="input-group">
<label for="distance">Afstand:</label>
<div class="input-row">
<input id="distance" placeholder="Enter distance" type="text" value="1"/>
<select id="unit">
<option value="feet">Miles</option>
<option value="meters">Kilometer</option>
</select>
</div>
</div>
</div>
<button class="calc-button" onclick="fresnelZone()">Beregn Fresnel-zone</button>
</div>
<div class="result-section" id="results">
<div class="section-header">Beregningsresultater</div>
<div class="section-content">
<div class="data-row">
<div class="data-label">Fresnel zone radius:</div>
<div class="data-value highlight" id="fnr">-</div>
</div>
<div class="data-row">
<div class="data-label">Center Point Placering:</div>
<div class="data-value" id="center">-</div>
</div>
</div>
</div>
<div class="info-box">
<h3>Om Fresnel Zoner</h3>
<p>
<strong>Hvad er en Fresnel-zone?</strong>Fresnel-zonen er et elliptisk område omkring den visuelle synslinje mellem to antenner. Radiobølger spredes ud, mens de rejser, og denne zone repræsenterer det område, hvor disse bølger kan interferere konstruktivt eller destruktivt.</p>
<p>
<strong>Hvorfor er det vigtigt?</strong>For at opnå optimal RF-link ydeevne bør mindst 60 % af den første Fresnel-zone være fri af forhindringer (bygninger, træer, terræn). Denne lommeregner hjælper dig med at bestemme den nødvendige frigangsradius ved midtpunktet af din trådløse forbindelse.</p>
<p>
<strong>Sådan bruger du:</strong>Indtast din driftsfrekvens og den samlede afstand mellem antennerne. Lommeregneren vil vise dig radius af Fresnel-zonen på det bredeste sted (midten af ​​linket).</p>
</div>
</div>
<script>
function fresnelZone() {
    // Set variables from input
    var frequency = Number(document.getElementById("frequency").value);
    var freunit = document.getElementById("freunit").value;
    var distance = Number(document.getElementById("distance").value);
    var unit = document.getElementById("unit").value;

    if (freunit == "ghz") {
        var sf = frequency;
    } else if (freunit == "mhz") {
        var sf = frequency/1000;
    } else if (freunit == "khz") {
        var sf = frequency/1000000;
    } else {
        var sf = frequency/1000000000;
    }


    var d1 = distance / 2;
    var d2 = d1;
    if (unit == "feet") {
        //var radius = Math.round(72.05 * Math.sqrt((d1*d2/(sf))));
        var radius = Math.round(36.03 * Math.sqrt((distance/sf)))
        var distunit = "Miles"
    } else {
        //var radius = Math.round(17.32 * Math.sqrt((d1*d2/(sf))));
        var radius = Math.round(8.657 * Math.sqrt((distance/sf)))
        var distunit = "Kilometers"
    }

    document.getElementById("fnr").textContent = radius + " feet";
    document.getElementById("center").textContent = "Located " + d1 + " " + distunit + " from the first antenna";

    // Show results section
    document.getElementById("results").classList.add("show");

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

// Add enter key support
document.addEventListener('DOMContentLoaded', function() {
    document.getElementById("frequency").addEventListener('keypress', function(e) {
        if (e.key === 'Enter') {
            fresnelZone();
        }
    });

    document.getElementById("distance").addEventListener('keypress', function(e) {
        if (e.key === 'Enter') {
            fresnelZone();
        }
    });
});
</script>