I did some testing Sunday evening to explore the performance envelope of the 50 watt amplifier and QCX+ combination. My friend who will be operating the set will be using batteries, so I wanted to explore the full range of voltages.
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My setup was a variable bench power supply, switch-mode variety, a mystery brand "Uniroi RC305" similar to many.? Current limit turned up? the limit of 5 amps, and using the supply's internal metering which I'd previously checked to be in agreement with my Fluke 115. RF power measurement? was by using my Siglent scope to measure peak to peak volts, squaring that and dividing by 400.? Dummy load was another mystery brand purchased on-line, said to be good for 10 watts continuous and 100 watts peak - so I kept my power measurements short and gave the dummy load a minute or so to cool between dits.? Exciter was the QCX+ at a constant 13.8 volts from a separate supply, giving about 4 watts into a dummy load. Test frequency was 3520 KHz.
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10 V 5.3 W
12 V 7.6 W
13.8 V 9.9 W
15.0 V 11.6 W
17.0 V 14.8 W
19.0 V 18.3 W
21.0 V 21.9 W
24 V?? 27.9 W
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I did have a shortwave receiver running in the next room and didn't notice any odd sounds coming from it, and the carrier looked clean visually.? I did not do FFTs at every voltage,? the 8-bit scope has a pretty limited range and I didn't think it would assure being 40 dB down at the second harmonic. I'll do this at 13.8 V just for educational value.
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I then put the QCX+ on the variable supply and the amplifier on fixed 13.8 V - sweeping the QCX from 10 to 15 volts gave no difference to the power output of the 50 watt amplifier, which remained at 9.9 watts.
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My new IRF510s came in today but in view of the recommendations of Aki JO4MTH, I don't think I'll swap transistors out.
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It's been very educational building and testing this kit. Thanks to the group for comments. Knowing when to stop tweaking is a vital skill.
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Bill
