Crawley Amateur Radio Club

For years inexpensive Digital Volt Meters (DVM) have been available to the amateur radio world. Professional ones are also available, but their prices are sometimes prohibitive to the amateur. In the professional world, four lead ohm-meters are used for measuring resistance. In a basic measuring set up with just two leads, the result is compromised by the resistance of the leads connecting the device under test (DUT), i.e. the resistor in this case to the DVM. It is particularly troublesome when trying to characterise low value resistors. If the leads have say 0.05Ω total resistance, and the DUT is a 0.1Ω resistor, the measurement will be wrong by 50%, as the DVM will show 0.15Ω instead of 1Ω. The way around this is easy to achieve with modern op-amps, and is achieved by using 4-wire Kelvin leads, some circuitry, and a DVM. The circuitry will need to provide a constant known current through the DUT from say a Jfet operating in constant current mode. This known current is connected such...

NavHam is a new website from Chris Barber (2E0UCB). NavHam provides a repeater and gateway locator for amateur radio operators in the UK. Find nearby repeaters and personal gateways on a live map, filter by mode and band, and get bearing and distance from your current location. Give it a try here: https://navham.co.uk/ Features include: Live map with all UK repeaters & gateways Gateways & hotspots directory — add your own Filter by mode (FM, DMR, D-STAR, C4FM…) & band Distance, bearing & compass view for the field Favourites & Top repeaters quick-access Coverage reports, fault reporting & station comments Submit repeaters & gateways for moderator review Leaderboard, community stats & onboarding points Testimonials wall & referral program Request features & see the planned roadmap My QTH: Maidenhead grid, WAB, OS grid, CQ/ITU zones

Radio propagation through the ionosphere is one of the great gifts nature gives to anyone with an antenna and a receiver. While most of us are familiar with the F layer's role in long-distance HF communication, the E layer — and especially its unpredictable cousin, Sporadic E — deserves its own detailed look. This piece covers both the traditional, well-behaved E layer and the wild, VHF-opening phenomenon known as Sporadic E, with an eye to what it means for CARC members working HF and VHF from here in West Sussex. Part One: Traditional E Layer Propagation What Is the E Layer? The E layer is a region of the ionosphere located roughly 90 to 150 km (56 to 93 miles) above the Earth's surface. It sits below the F layer and above the D layer, forming one of several ionized layers that make radio propagation possible. The "E" designation comes from the original naming convention used by physicist Edward Appleton, who studied the layers using "electric" wave ...