Binoculars & Telescopes

The short answer The BTECH GMRS-V2 is our starting recommendation for long range walkie talkies: it combines repeater capability, a removable antenna, and a relatively accessible price. Choose the Rocky Talkie Expedition Radio for a simpler, waterproof outdoor setup, or the Rocky Talkie Mountain Radio when your group needs license-free operation. The important distinction is […]

A Schmidt–Pechan prism is a compact roof-prism optical system that rotates an inverted image by 180 degrees so it appears upright and correctly oriented. Its folded light path keeps the entrance and exit beams nearly coaxial, which is why the design is widely used in modern compact binoculars. Quick Specifications Characteristic Schmidt–Pechan system Image rotation […]

Moxon antenna calculator: dimensions, plans, and tuning guide. Use this Moxon antenna calculator to generate the A–E dimensions for a classic 2-element Moxon rectangle from your design frequency and conductor diameter. Choose common amateur-radio bands or enter a custom frequency, then use the plans, construction notes, tuning steps, gain and radiation-pattern guidance below to turn the calculated geometry into a practical antenna.

Calculate the vertical and horizontal wire lengths for a half-square antenna, choose a corner-fed or end-fed configuration, and use the results as practical starting dimensions for building and tuning your antenna.

Calculate the wire length, side dimensions, loop height, wavelength, and quarter-wave matching section for a delta loop or other full-wave loop antenna. Enter your operating frequency, choose the loop geometry, and use the calculated dimensions as a practical starting point for construction and tuning.

EFHW antenna calculator: end-fed half-wave design and length

OCFD Dimensions, Design & Plans. Calculate the total length, short leg, long leg and feedpoint position for an off-center-fed dipole. Choose a band or custom frequency, select the OCF split, and use the results as a starting point for building and tuning your antenna.

Calculate section lengths for a multiband linked dipole, standard dipole, or inverted-V antenna by frequency. Enter the HF bands or exact operating frequencies you want to use. The calculator returns the starting cut length for each dipole leg, individual linked sections, link positions, and the complete active antenna length for every band. Linked dipole geometry […]

Direct expert answer There is no fixed “20 km range” specification for binoculars: a binocular does not stop working at a particular distance. At roughly 12 miles, usable detail depends on magnification, optical resolution, atmospheric haze and heat shimmer, target contrast, and—critically—image stability. For serious long-distance terrestrial observation, 15×56 is the most balanced configuration in […]

← Part I: from the Tower of Babel to Tsiolkovsky’s dream Part II: how a Dream Became an Engineering Calculation ⟶ Chapter 13. The major engineering dead ends: why aren’t we in orbit yet? The turn of the millennium brought not just an understanding of the underlying physics, but also a harsh collision with the […]