AM 4MHz SW Band Marker/Transmitter

This is a sister version of "1308kHz Amplitude Modulator Board" for SW Band 4MHz. The circuit was a bit modified but almost the same, very simple and easy to make. There are two advantages to listen Oldies with vintage tube radio. No.1 SW band contains less digital noise than MW Band in a house normally. No.2 4MHz can also be used as the marker of 8Mhz and 12MHz for the harmonics so that you can make a correction of the tuning position.

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