Figure 1, below, shows the 10.58 to 10.74 MHz VFO oscillator circuit. Yes, this is the aforementioned ambit that was presented aftermost time, but I’ve re-drawn it to appearance the Colpitts oscillator added clearly. “L” is about 1.5 uH; 19 turns in a T50-6 amount (yellow). The amount of C6 is begin experimentally. I acclimated 69 pF (a 47 pF and a 22 pF in parallel). Added about this during check-out.
10.58 to 10.74 MHz VFO Oscillator Circuit
“L” and the V V C forth with C6 accomplish up the parallel-tuned ambit that determines the abundance of the VFO. The V V C is an MV2104. Capacitors apparent with an asterisk charge be silvered mica, COG, or NPO.
You ability admiration how the basic ethics for the beating ambit are determined. Well, back Jupiter is accumbent with Mars, and Mercury is on the bend of a new moon, if the anterior reactance equals the capacitive reactance, again we accept a beating circuit. For any accustomed abundance there are amaranthine combinations of L and C that will aftermath a beating circuit. Experience shows that capricious capacitors and V V C’s in the 5 pF to 300 pF ambit are altogether practical. Combine this with the actuality that a 1.5 uH braid and a 150 pF capacitor bell abreast the abundance of interest, and you accept the basic ethics for this VFO’s beating circuit. You can acquisition formulas for addition all this out in your Handbook, if you like to do arithmetic. The basic ethics absolutely acclimated in the ambit booty into annual “stray” inductance and capacitance that occurs in the absolute world. Added about this during check-out.
RESONANT CIRCUITS are alluring critters! While I’m NOT activity to get into a abstract discussion, there are some axiological characteristics of beating circuits that you (and I) should accumulate in apperception back architecture VFO’s, filters, RF amplifiers, etc.
Two types of beating circuits are frequently used: alternation beating circuits and alongside beating circuits, as apparent below. Here are two important things to accumulate in mind: PARALLEL beating circuits abate the breeze of AC accepted at the beating abundance (and canyon all added frequencies); SERIES beating circuits canyon AC accepted at the beating abundance (and abate all added frequencies).