Butler Oscillator

  
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My first tasks involved buying some VHF parts + exploring the Butler crystal oscillator. Specifically, I`ll cover my experiences with the common base version of the Butler oscillator. Like HF, the VHF knowledge base contains ever-present lore. Consider the Butler oscillator ” I have read arguments stating that the emitter follower version of the Butler oscillattor
Butler Oscillator - schematic

is vastly superior to the common base version because the latter is prone to UHF and other spurs. These comments seem to have originated from a good book entitled Crystal Oscillator Circuits. While examining the schematics of professional/world class gear using a Butler, the common base version clearly dominates. Spectrum analysis and other measurements indicate that when common UHF oscillation management techniques are applied, common base Butler crystal oscillators work well. Suppressing UHF oscillations with ferrite beads (and small value resistors), feedback, neutralization, limiting gain, etcetera are routine practices for us experimenters applying active devices that have strong gain into UHF on up. This is vanilla, or matter-of-fact construction for us; no worries. While fun and often convenient, lore ultimately stifles our progress. Increasingly, I`m adopting the philosophy of Bob, K3NHI; "TMITK" ” to measure is to know. Consider, too, you have to know what to measure and possess the required gear. For JFETs, the J310 in TO-92 and SMT will remain my workhorse FET part along with a couple of other low noise JFETs and 2-gate MOSFETs. At VHF, the noise figure in a receiver chain is established by the first amplifier so a low noise preamp ranks important. A collection of 100 volt NP0 capacitors ranging from 1 pF to 22 pF were added along with some chip and SMT caps as low as 0. 5 pF. You might need a few air trimmer...



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