Friday, July 17, 2009


Now we are getting somewhere. Frequency for the subharmonic L.O. reached. I actually got two parameters to play with for frequency adjustment, the capacitor in series with the crystal and the supply voltage of the ocillator. This is actually adjusted and measured at 5V. Oscillation stops at about 4V. The circuit itself however, is designed for stabilized 8V. Thus, here are some degrees of freedom for the final tuneup.

As a last resort, I blamed it on the crystal, as suspected before. The crystal I used in the first attempt was not good, as shown by the replacement which more of less on the spot produced the correct frequency. Ouf! I need to build myself a crystal tester, I guess. Could possibly spare me some sleepless nights ;-)

The signal itself is not that perfect yet. I will have to install some resonating filter, I guess, to smooth out those humps and bumps to something that comes closer to a sine-wave than that...
Finally, the Poliakov-type mixer works best with a well balanced sine-wave.

Oh, and if you are interested in what I actually used for transistor, it's a 2N2222A. The rest of the bits and pieces are somewhat obvious and not worth to be mentioned individually...