{"product_id":"half-wave-dipole-formula-slate-coaster","title":"Half-Wave Dipole Formula Slate Coaster","description":"\u003cp\u003eA beautifully detailed slate coaster for radio enthusiasts, laser engraved with the classic \u003cstrong\u003ehalf-wave dipole formula\u003c\/strong\u003e: \u003cstrong\u003eL(m) = 150 × VF ÷ f(MHz)\u003c\/strong\u003e. This formula is used to calculate the total length of a half-wave dipole antenna, where \u003cstrong\u003eL\u003c\/strong\u003e is the overall end-to-end antenna length in metres, \u003cstrong\u003eVF\u003c\/strong\u003e is the velocity factor of the wire or material being used, and \u003cstrong\u003ef\u003c\/strong\u003e is the operating frequency in megahertz.\u003c\/p\u003e\n\u003cp\u003eFor ham radio operators and short wave listeners, the half-wave dipole is one of the most trusted and widely used antenna designs. It is simple, effective, and a great starting point for building antennas for HF bands such as 40m, 20m, 15m, and 10m. The engraved diagram shows the dipole split into two equal halves, making it a useful visual reminder that each side of the antenna is approximately \u003cstrong\u003eL\/2\u003c\/strong\u003e from the centre feed point. Practical, decorative, and full of radio heritage, this coaster is ideal for the shack, workshop, desk, or as a thoughtful gift for anyone who enjoys amateur radio or short wave listening.\u003c\/p\u003e\n\u003cp\u003eThese coasters are supplied with four soft adhesive feet so they do not mark surfaces. Putting four or six together would make an ideal gift.\u003c\/p\u003e\n\u003ch3\u003eProduct Features\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003ePrecision laser engraved design\u003c\/li\u003e\n\u003cli\u003eCrafted from natural grey slate\u003c\/li\u003e\n\u003cli\u003e10cm diameter and 4mm thick slate coaster with a rustic bevelled edge\u003c\/li\u003e\n\u003cli\u003eSoft sponge feet included\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003ePlease note slate coasters are not dishwasher safe.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan style=\"text-decoration: underline;\"\u003eDesign Copyright Notice\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eAll designs are the intellectual property of Primary 9 Designs and are protected by copyright.\u003c\/p\u003e\n\u003cp\u003eThese products are supplied for\u003cstrong\u003e \u003c\/strong\u003epersonal use only. The designs may not be reproduced, copied, distributed, modified, or used to create products for resale without prior written permission from Primary 9 Designs.\u003c\/p\u003e\n\u003cp\u003ePurchase of this item does not transfer copyright or grant a commercial licence to reproduce or sell the design in any form.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan style=\"text-decoration: underline;\"\u003eLarge Orders\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cspan\u003eLooking to order larger quantities? We are happy to provide bespoke lead time and shipping quotations for bulk orders, schools, clubs, care homes, events and organisations. Please contact us and we'll help find the most cost-effective shipping option for your order.\u003c\/span\u003e\u003c\/p\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cp\u003e \u003c\/p\u003e","brand":"Primary 9 Designs","offers":[{"title":"Default Title","offer_id":58373130649945,"sku":"4SLT10CR-HWA","price":4.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1007\/9230\/3961\/files\/IMG_3287.jpg?v=1782138187","url":"https:\/\/primary9designs.com\/products\/half-wave-dipole-formula-slate-coaster","provider":"Primary 9 Designs","version":"1.0","type":"link"}