G4PVB Amateur Radio St Albans
QRP output indicator for end-fed antennas.
TX tuning without a visual reference is like winking at a pretty girl in the dark. You're full of good intentions but it's a wasted effort. G8ATO/Norman: "WWII radio spy sets used car/domestic/pygmy light bulbs wired in series with the LW antenna to aid tuning. Tuned up with peak of brightness in the light. No specialised knowledge required."
K7HKL inspired project for QRP TX with basic LC tuner to LW antenna. Insulated LW antenna wire is passed through a ferrite ring (typically 35 mm diameter Fair-Rite 43 material from Radio Society of Great Britain 5) upon which several turns of insulated wire are wound and connected to LED - polarity not relevant. Mine: 5 mm red extreme brightness LED (easier to see on a sunny day) Maplin stock code N69AJ 9. Use blue/yellow hookup wire abandoned on pavement near distribution boxes. Stays in place yet able to be wound on the toroid. Silicone sealant secures.
Project box with PL259, SO239 connectors and wander plug for LW antenna illustrated. Alternatively a bank tellers' change bag for free if you ask nicely: "Happy counting." Tight fit black 2 core appliance flex sheath used to aid strain relief where antenna wire enters PL259. Think of the PL259 as a wander plug with a case.
Key the TX & observe the LED as you adjust your tuner. It glows maximum brightness at optimum tuning. This basic simple method (not component critical) is ideal for setting up a QRP station outdoors. New take on an old idea. < fiver. Text and picture in the public domain so feel free to copy & distribute. You can tune a radio but you can't tuna fish! MTMBWY G4PVB/Bob 25th January 2016
TX Transmitter | LW Long Wire | QRP Low Power
LC Inductor Capacitor | LED Light Emitting Diode
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