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Adding CW to bitx

June 24th, 2009 Comments off
Bitx Cw module

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.

bitx20 CW module

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

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.

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Manhattan Style construction for Hobbyists

May 7th, 2009 3 comments

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.

050720093144

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).

ckt 050720093154

Make a pad layout next from the above layout.

050720093155 050720093145

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.

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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.

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Finally, fix the transistors. You circuit is ready for testing .

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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.

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