QCX assembly Rev 1.08
65
Adjustment of the C1 trimmer capacitor should change the size of the amplitude bar. You need to
adjust the C1 trimmer for MAXIMUM amplitude. When this is done, the peak of the band pass filter
will be centred on the CW section of the band.
It is very important to understand the number at the top right of the LCD, here shown as 09. This is
an amplitude scaling factor, expressed as a power of 2. In this example, the actual amplitude is
divided by a factor of 512 (2 to the power of 9) then displayed on the screen. In this photograph,
27 little vertical bars are shown, which means the actual measured amplitude value is 13,824.
If the displayed bar drops below one third of the width of the LCD, then the division factor is
reduced by one and the bar is re-displayed. On the other hand, if the displayed bar overflows the
right edge of the screen, the division factor is increased by one. This simple method creates an
auto-scaling display of the amplitude.
Therefore, to peak the band pass filter trimmer, first adjust the trimmer potentiometer while looking
at the division factor in the top right of the LCD. Then carry out the fine adjustment using the
displayed amplitude bar. The peak is quite sharp.
Be wary because there can be more than one peak (more than one response of this simple band
pass filter). So, tune the trimmer capacitor through its whole range, and determine the maximum
scaling factor that you see. In my case here, it is 09. Then make the very fine adjustment
necessary to peak the amplitude bar.
When you have peaked the response, check carefully that the C1 trimmer capacitor is not at either
end of its range. If it is, this means the resonant circuit is NOT correctly peaked. You need to
adjust the number of turns on the long secondary winding of the T1 transformer. Visual inspection
will show clearly whether or not the trimmer capacitor is at the end of its range.
Perfect!
OK! The plates of the trimmer capacitor are somewhere nicely in the their
range, not at the minimum or maximum capacitance. You have found the
peak response of the BPF and all is well.
Plates completely closed
Here the fixed and movable sets of capacitor plates are completely meshed,
resulting in the highest capacitance. It means MORE inductance is needed.
So carefully unsolder one end of the secondary 3 winding of T1, join a piece
of wire, and win
d it 5 more turns through the toroid. Then try again. Don’t
worry if it looks a bit messy.
Plates completely open
Here the fixed and movable sets of capacitor plates are completely
unmeshed, resulting in the lowest capacitance. It means LESS inductance is
needed. So carefully unsolder one end of the secondary 3 winding of T1,
remove 5 more turns through the toroid, and resolder. Then try again.
Summary of Contents for QCX 5W CW
Page 9: ...QCX assembly Rev 1 08 9...
Page 10: ...QCX assembly Rev 1 08 10...
Page 12: ...QCX assembly Rev 1 08 12...
Page 50: ...QCX assembly Rev 1 08 50...
Page 105: ...QCX assembly Rev 1 08 105...
