Variable Frequency Oscillators (VFOs)

1. Chapter 10, Harris CRYSTAL SETS TO SIDEBAND. Frank W. Harris 2010, REV 12. Chapter 10. Variable Frequency Oscillators (VFOs). Sooner or later you'll become frustrated with being stuck on a few crystal-controlled frequencies. You would like to have a Frequency -tuning knob that covers the entire band and not just a few kilohertz. This sounds simple, but isn't. It's difficult because, without the stability of a crystal, an ordinary RF oscillator will drift hundreds of hertz while you're sending. The fellow you're talking to probably has a modern transceiver with a narrow, stable passband. From his perspective your signal quickly drifts out of his passband. His digital readout may be calibrated to tenths of a Hertz and he will take great delight in telling you about YOUR PROBLEM. Drift is a big deal today In the old days, like 1950, receiver passbands were usually huge, like 10 or 20 kilohertz.

Secret # 1. Junction Field Effect Transistors (JFETs) The first secret of a stable VFO is using a JFET instead of a bipolar transistor. As described earlier, a field effect transistor is better because it is less sensitive to temperature. I have used 2N3823, 2N5484 and 2N4416 N-channel JFET’s for VFO oscillators.

Loading..

Tags:

  Field, Transistor, Effect, Junction, Jfet, Field effect transistor, Junction field effect

Information

Related search queries