Measurement of the signal quality of QRP-Labs U3s with low-pass filters.Transmitter output is fed into a homemade 40dB power pad. The spectrum is measured using an SIGLENT SSA3021X analyzer.
The bias voltage was about 2.6VDC and the PA voltage was abt. 7VDC.

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40m  40m 10kHz  40m 100kHz 40m 1MHz

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20m 20m 10kHz20m 100kHz 20m 1MHz

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6m  6m 10kHz   6m 100kHz 6m 1MHz

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2014 CW (Morse Telegraphy) was added to the German Nationwide Inventory of Intangible Cultural Heritage.