Bill of Soldersmoke has posted a very neat hack for the BITX40. An outboard analog VFO! It is as simple as it is clean and good. If you happen to be lucky enough to own a nice variable capacitor, this probably the one hack you need to make to your BITX!
So, this is, simply the VFO that he built :
It looks like this
Read more about his hack on soldersmoke blog .
COPPONONTS VALUES/COIL WINDING DETAILS ARE INCOMPLETE :-
ReplyDeleteCOIL, FET , S1 DIODE, O/PUT CONDENCER VALUE Etc
Generally speaking, the component values not shown are determined by a combination of factors, most importantly the wavelength we want to use the vfo on, and the value of the available variable capacitor that constitute the L/C "tank" circuit, in this case the one shown as 200 pFd.
DeleteAny value between 250 and 100 pFd. will work for HF work; however, we generally want larger values for longer wavelengths, and lower ones for higher wavelengths.
The coil is then wound to put the rig on frequency, and the tap adjusted to provide good feedback for oscillation.
The output capacitor is pretty clearly shown as a 10 mFd ceramic, but the value is not terribly critical.
If you are going to attempt to duplicate this design, you will go nuts trying to line up the exact values. All homebrewing involves some experimentation and measurement to determine if the values on hand can be made to work.
Good luck. It may seem daunting, but it isn't that hard!
Loovely post
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