Set of Four Radio Formulae Slate Coasters

Buy all four Radio Formulae Slate Coasters as a set for a special price!

Ohm’s Law Power Formulas Slate Coaster

A practical and eye-catching slate coaster for radio enthusiasts, laser engraved with essential Ohm’s Law and power formulas: V = I × R, P = V × I, P = V² ÷ R, and P = I² × R. These formulas describe the relationship between voltage, current, resistance, and power — the core electrical principles behind transmitters, receivers, antennas, power supplies, dummy loads, and test equipment.

For ham radio operators and short wave listeners, these calculations are genuinely useful at the bench or in the shack. They help when checking current draw, estimating power dissipation, choosing suitable resistors, understanding dummy loads, or working out whether equipment and cables are being operated safely. Laser engraved into natural slate, this coaster combines a rugged technical look with a handy reference that feels right at home beside a transceiver, soldering station, or workshop mug.

Decibels Power Ratio Slate Coaster

A smart and technical slate coaster for radio enthusiasts, laser engraved with the essential decibel power ratio formula: dB = 10 log₁₀(P₂ ÷ P₁). This formula is used to compare two power levels, where P₁ is the input power and P₂ is the output power. In amateur radio, decibels are used everywhere — from antenna gain and feeder loss to amplifier performance, filters, attenuators, and signal strength comparisons.

For ham radio operators and short wave listeners, understanding dB makes it much easier to judge what a change in equipment or antenna system really means. A small number of decibels can represent a meaningful change in power or received signal, while larger values quickly show major gain or loss. The engraved gain diagram and S-meter style graphic make this coaster both a useful reference and a great shack accessory. Laser engraved into natural slate, it has a rugged radio-room look that is ideal for an operating desk, workshop, or gift for anyone interested in RF, antennas, and signal performance.

Half-Wave Dipole Formula Slate Coaster

A beautifully detailed slate coaster for radio enthusiasts, laser engraved with the classic half-wave dipole formula: L(m) = 150 × VF ÷ f(MHz). This formula is used to calculate the total length of a half-wave dipole antenna, where L is the overall end-to-end antenna length in metres, VF is the velocity factor of the wire or material being used, and f is the operating frequency in megahertz.

For 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 L/2 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.

Quarter-Wave Antenna Formula Slate Coaster

A stylish and practical gift for radio enthusiasts, this natural slate coaster is laser engraved with the classic quarter-wave antenna formula: L(m) = 75 × VF ÷ f(MHz). This formula is used to calculate the approximate length of a quarter-wave vertical antenna or radial, where L is the antenna length in metres, VF is the velocity factor of the material, and f is the operating frequency in megahertz.

For 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.

These coasters are supplied with four soft adhesive feet so they do not mark surfaces. Putting four or six together would make an ideal gift.

Product Features

• Precision laser engraved design
• Crafted from natural grey slate
• 10cm diameter and 4mm thick slate coaster with a rustic bevelled edge
• Soft sponge feet included

Please note slate coasters are not dishwasher safe.

Design Copyright Notice

All designs are the intellectual property of Primary 9 Designs and are protected by copyright.

These products are supplied for personal 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.

Purchase of this item does not transfer copyright or grant a commercial licence to reproduce or sell the design in any form.

Large Orders

Looking 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.