{"product_id":"slate-coaster","title":"Quarter-Wave Antenna Formula Slate Coaster","description":"\u003cp\u003eA stylish and practical gift for radio enthusiasts, this natural slate coaster is laser engraved with the classic \u003cstrong\u003equarter-wave antenna formula\u003c\/strong\u003e: \u003cstrong\u003eL(m) = 75 × VF ÷ f(MHz)\u003c\/strong\u003e. This formula is used to calculate the approximate length of a quarter-wave vertical antenna or radial, where \u003cstrong\u003eL\u003c\/strong\u003e is the antenna length in metres, \u003cstrong\u003eVF\u003c\/strong\u003e is the velocity factor of the material, 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, antenna length is one of the most important factors in getting strong, efficient reception and transmission. A quarter-wave vertical is a popular antenna design because it is simple, compact, and effective across many bands. Whether used as a shack coaster, workshop reference, or conversation piece, this engraved slate design combines radio heritage with genuinely useful technical information. Its dark natural stone and crisp engraving make it ideal for any radio room, desk, or operating position.\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":57561923289433,"sku":"4SLT10CR-QWA","price":4.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1007\/9230\/3961\/files\/IMG_3285.jpg?v=1782137888","url":"https:\/\/primary9designs.com\/products\/slate-coaster","provider":"Primary 9 Designs","version":"1.0","type":"link"}