30m Oscillator (Night 4)

I found some bench time after the family shared a movie Saturday night and went to bed.






I did a bunch of testing and made some changes.

• 
  I tweaked the gain stages slightly. Q3 and Q4 seem to operate more efficiently with
  a 100 ohm resistor instead of the 10 ohm resistor. I validated both values with the
  spectrum analyzer and I got a bit more gain of the fundamental frequency and less
  impact on the harmonic frequencies.


• 
  In talking with N0FP earlier in the day I discovered that my output at 50 ohms was
  loading the final transistor. I played with using a matching transformer but was unhappy
  with the result. (I think that I was getting tired and should retest the process with
  the transformer again.)
  
  
  


• 
  I also tried changing the output from a common-emitter to a common-collector. The
  common-collector design has a lower output impedance and was a better match to the
  50 ohm load. It was a not a perfect match @ 4:1 but it was pretty decent and reduced
  the amount of loading. (In the end I left it as a common-emitter design for now.)


• 
  I then relocated the low pass filter from after Q2 to it's new home after Q4. I tried
  using a 4:1 transformer from the collector to the input of the filter but was running
  into some flaky issues. I experimented again with common-emitter vs. common-collector
  to try to get a better match. In the end the common-emitter design worked pretty well
  so I left it alone.

Results:

• 
  Power is now running about  3.2mW or ~ +5dBm. (I referenced the spectrum analyzer
  against my signal generator and then compared the final output of the transmitter.)


• 
  My harmonics are down 55dB against the fundamental frequency. (It would be legal to
  put on the air as is.)

Next steps:

• 
  Look at some more options to increase the power into the 100-200mW range.


• 
  Add a key (RCA or 1/8" jack) so that I can try to make a QSO with it.