Bitx Cw module
I was playing with my bitx build yesterday. Specifically, I tried to add CW to the rig. Original bitx20 is a SSB rig. I my mod was inspired from PY2OHH bitx40. I wired up a 10mhz crystal oscillator as shown below.
The idea is to inject 10mhz ( approximately) at the beginning of transmitter IF amplifier. This will in turn produce 14 mhz sine wave at the output. The receiver part is unmodified. See the diagram below. Connect the point marked X to the point x .
Bitx 20 modified for cw
Adjust the 10Mhz oscillator to around 700khz above the BFO frequency. I added a small inductor (10 micro henry) in series with the crystal to adjust the frequency near BFO,.It is not shown on the figure above.
Most of the home brewers and electronics hobbyist see fabricating a PCB as a roadblock . I will describe an alternate approach to circuit construction where you need only bare copper clad sheet. This method is some times called Manhattan method.( I don’t know the reason.)
The basic ingredients you need for this type of construction is bare copper clad sheet. Either glass epoxy or paper phenolic boards can be used. As the first step take a small pieces of copper clad sheet and chip it into small pads. There is no minimum size or maximum size . Use a sharp tool like a chisel for cutting the board. Some sample pieces that I made is shown in the figure below. If you have access to a sheet metal cutting tool, it is very easy to make them. I keep a small box of such PCB chips.
Collect all the components that you need for construction. Study the circuit you are planning to build and make a rough layout of component placement on paper. Pay special attention to the size and shape of the components you are planning to use. If possible, make the circuit layout section by section . This will make debugging easier. The circuit will be fabricated on a a plain copper clad sheet .The copper clad sheet will be the ground of your circuit Keep this in mind when you make the sketch. Here is the circuit and a rough sketch I made for constructing bitx20. ( This is RF preamplifier stage of bitx20).
Make a pad layout next from the above layout.
The size of the copper clad sheet needed can be roughly estimated if you have some idea about the components. Cut a sufficiently large piece of copper clad and then clean it properly. Affix the pads using super glue. Any other adhesive used in electronic repair can be used.
Now start soldering . Make sure that the pads are clean. I use a sharp knife to clean the pads. Start with the resistors. Keep the leads small.. Next , solder the capacitors followed by other low foot print components.
Finally, fix the transistors. You circuit is ready for testing .
There are several advantages to this type of construction. The plain copper clad sheet will act as a ground plane and will improve the performance of RF circuits. Also, If you want to replace a faulty component it is very easy.