QRPKits BITX20A, Инструкции по преобразованию

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VFO Circuit
Bias for Q­7 is developed from the same two resistors (R­33 and R­34) that provide bias for Q­8.
Main frequency determining components of the VFO include L­7, C­34 & C­35, C­15, C­37, C­90, and
C­38. D9 acts as a voltage variable capacitor in series with C­39 to provide Fine Tuning control. For
adequate VFO stability C­34, C­37, and C­35 should be polystyrene types (these are semi­transparent
plastic). C­15, C­39, and C­90 should be NPO types (they have a black band on the top section).
For operation on 17 meters, the VFO operates 12.96 MHz below the desired frequency (18.068 – 12.96
= 5.108 MHz and 18.168 ­12.96 = 5.208 MHz) so the VFO needs to tune over the range of 5.108 to
5.208 MHz. VFO alignment steps are:
1. Set the Fine Tune potentiometer to mid­point.
2. Open C­38 (the polyvaricon) to minimum capacitance.
3. Adjust C­38 trimmer capacitor so the VFO is operating at or just above 5.208 MHz. If you
cannot reach that frequency, try changing the values of C­90, then C­37, and lastly C­15.
4. Close C­38 (the polyvaricon) to maximum capacitance and verify that your VFO frequency is
now below 5.108 MHz.
Waveforms present in this oscillator will affect the accuracy of DC voltmeters. In order to measure
these potentials you should stop the oscillator by temporarily connecting a 0.1 mfd capacitor across
R­36.
Q­8 Voltages Q­7 Voltages Q­6 Voltages
Collector 9.13 VDC Collector 9.13 VDC Collector 7.98 VDC
Emitter 3.75 VDC Emitter 3.64 VDC Emitter 3.16 VDC
Base 4.40 VDC Base 4.29 VDC Base 3.88 VDC
(Remember to remove the 0.1 that was installed to stop the oscillator)
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