KA7OEI's blog

Random musings - usually on a technical (nerdy) subject - perhaps related to amateur radio and things found at ka7oei.com and modulatedlight.org

Wednesday, February 25, 2026

Impedance matching (auto) transformer and common-mode choke for the JPC-7 dipole and other electrically-short (loaded) dipoles and verticals

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Figure 1: The JPC-7 loaded dipole out in the wild! Click on the image for a larger version. Loading coils and "electrically-short"...
Friday, January 23, 2026

How I prevented QRM to HF reception from my solar and AC inverter at Quartzfest

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Figure 1: White board from Quartzfest! Click on the image for a larger version As it happens, I found myself at QuartzFest in Arizona in t...
Thursday, December 25, 2025

Neon bar-graph VSWR/Power meter using the ИН-13 (a.k.a "IN-13") "Nixie" - Part 3 (of 3)

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Figure 1: Power/VSWR meter using ИН-13 neon bar-graph indicators. This was taken prior to installing the dark plastic to improve contrast ...
Thursday, November 27, 2025

Adding ALC and overdrive protection to the MFJ ALS-500M "500 watt" amplifier

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Figure 1: The ALS-500M front panel.  Because this this unit is equipped with the 10 meter low-pass filter, the "AUX" position on t...
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