Quote:
Originally Posted by 1100 man
Second anomaly concerns the coils. One winding has a tapping which I assume is the primary? This is fairly obvious for L1, the oscillator coil but not so for L2, the aerial coil.
I would have assumed that the primary (the side with three pins) would be connected to the BC109 with the tapping unused. The secondary with two pins would go to the 270pf cap and the aerial.
Looking at your PCB layout, it looks like your L2 coil is connected the other way round- ie the three pin side goes to the aerial?
Nick
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Hi Nick,
Yes, the tapped winding of L2 goes to the aerial, but the tap isn't used. I can best quote from the article, which makes this clear, and I've annotated the component placement sketch of the PCB I designed, which uses exactly the same layout and connections as does Ian's original PCB.
Here's a quote from the original article:
'L1 & L2 are both 90µH variable inductors. These are tapped at 25% from one end and have a low impedance secondary winding. The secondary is not used in L1 and the tapping is not used in L2. One end of L1's winding should be grounded to aid frequency stability'.
End quote.
The sketch below will hopefully make this clearer.
I've also attached the original circuit so it can be compared with the layout.
Good luck with the project Nick!