I solved my stability problem for the Hendricks Bitx20A kit by applying the Martiens mod. Now I need to resolve a low power output problem. I had been just calculating the power output from my peak to peak O-Scope readings with a 10x probe. However I notice that while I had 70 VPP on the scope with the 10x probe ( ~ 12.2W = (70^2)/400 ); my wattmeters both read a much lower 4 to 6 watts. My wattmeters are a NorCal QRP Club watt meter and a Heathkit HM-9 QRP Wattmeter. I am driving the microphone input with a 600 Hz phase shift sine wave oscillator.
Interestingly, when I switch to 1X on the probe my reading drops to 42 VPP which calculates out to 4.4 Watts and is more inline with the external wattmeters. My scope is a new Siglent 200 MHz dual trace digital unit, with stock 10x/1x probes.
I have been reading up on scope probes and it seems that my 200 MHz probes are good to 200 MHz only in the 10x position. In 1X the spec says 6 MHz, well below the 14 MHz carrier. Based on this alone I would tend to accept the 70 VPP reading as accurate and accept that I am getting 12W out. However given the lower readings from the external wattmeters I am not sure what to believe.
I have a homemade -20 db coupler that when terminated to 50 ohms at the tap and fed to the scope with RG-58 also agrees with the lower power output.
My older 20 MHz analog scope agrees with the lower 42 VPP / 4.4W readings independent of the 10x/1x setting. (Calibration of this scope is reasonable but not traceable. )
All readings into a 50 ohm dummy load.
What am I missing?