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Monday, March 31, 2014

Bitx3B VFO

The Bitx3B has a Varactor tuned VFO using MV209 and the stability is controlled with the Ik3OIL FLL Freq counter which has an inbuilt software to correct the drift in the VFO.

Building a stable vfo is an art and if not built correctly it would not perform optimum.

Picture and Video  below outlines some important factors that could enhance the performance.

BITX 3 B VFO SECTION

Outlined below are some points that need to be performed on the VFO section of Bitx3b for a drift free VFO

1.  VFO Capacitors to be NPO or Polystyrene

2. L5 VFO coil to be wounded tightly, placed flat on board and   applied  with thin layer of glue, quick fix is preferred as it has a thin layer, not very much to be applied, just enough to cover it.

3.MV209 And BB204  legs to be trimmed so that they may be just about near the board and soldered. A thin coating of quick fix could be applied on their sides, this way it becomes a sealed unit and gets protection from any air currents to extremely temperature.

4.It is better to use X position with 0.1uf  preferred Silver Mica /NPO or Polystyrene capacitor.  If you place a jumper across X then you may experience some drift, with 0.1uf in place the drift is manageable with the FLL counter attached.

5.  For FLL Freq counter Input and Contol it is recommended to use Rg174u coax

 6. Adjustment of Trimmer on control side of FLL is very important. The trimmer on extreme end of board is the trimmer that connects to the FLL control unit. Remember to fully mesh the trimmer or the vfo may drift.

The vfo was tested using the above recommendations and the test results:  2 Hours VFO On with max drift of 25Herts 




                   

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