Harmonic content of mcHF's output

From time to time I've read comments on various forums that mcHF transceivers should not be used with amplifiers because of the high harmonic content on the output.

I almost always use an amp with mine when operating from home so I decided to measure my  mcHF. My amp, a Hardrock-50, contains its own lowpass filters on the output so I was never concerned with whether or not the mcHF was "dirty".

Here are the results, made with a recently (July 2020) calibrated HP-8563A spectrum analyzer.

Each horizontal line represents 10dB. So the top line, where the fundamental is placed, is the reference or 0 dB. The next line down from that is -10dB, then -20dB, etc.

I've put a delta marker on the first harmonic and it's easy enough to count down from the top of the display to see the attenuation of subsequent harmonics, keeping the 10dB per line in mind.

Cheap DC-DC converter for QRP with batteries

My recent outtings with the mcHF on battery power have made me realize, once again, that there is always a compromise to be made when matching battery type to the rig's maximum safe input voltage level. Quite often, a 3S battery will be a couple of volts less than the radio's maximum level but a 4S pack will exceed the radio's rating.

The ramifications are minimal and may not seem to make a significant real-world difference but consider the 25% variation in maximum permissible input voltages of several QRP rigs:

• mcHF - 16v
• KX2, KX3 - 15v
• Anan-10E - 14v
• MTR-3B - 12v

A battery that is safe to use with an MTR-3B will underpower my mcHF, decreasing its 10-watt output to 6 watts.