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| Low Cost ½ λ Dipole |
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| Telephone Drop Wire |
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| Underwriter's Knot |
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Low-cost ½ λ Dipole for HF QRP rigs
Here’s an economical dipole for simple QRP HF homebrew rigs. It’s a one-piece radiator/feeder arrangement made of surplus insulated telephone drop wire with twin copper-clad steel cores.
The cores are separated to get the λ/2 radiating length and then tied together with string to arrest further separation.
The string could be done away with, and the λ/2 length yet maintained, using the reliable 'Underwriters Knot'.
The end insulators are scrap bakelite pieces, drilled to take the wire and string. Banana plugs are used at the rig-end.
Works real good when strung high up between two trees or other supports.
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Improved 7 MHz QRP CW Rig
This QRP CW transmitter's output is of the order of 5W.
Fairly comfortable QSOs are possible with the higher power level. The driver and the final transistors require heat sinks. The aluminium enclosure serves as the heat sink for the final.
The variable capacitors, coil cores and 100Ω potentiometer are adjusted for maximum clean output.
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| Improved 7 MHz QRP CW Rig |
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| Improved 7 MHz QRP CW Rig - Schematic |