Colpitts

L1C1 are selected to be resonant at a frequency below the desired crystal harmonic but above the crystal"s next lower odd harmonic. C2 should have a value of 30-70 pF, independent of the oscillation frequency. There is no requirement for any specific ratio of C1/C2, but practical harmonic circuits seem to work best when Cl is approximately 1-3 times the value of C2. Diodes D1-D3 provide a simple regulated bias supply..

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Bias for the pnp bipolar transistor is provided by resistor voltage divider network R1/R2. The collector of the oscillator transistor is kept at ac ground by capacitor C5, placed close to the transistor. ..

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A tapped-coil Colpitis oscillator is used at Ql to provide four tuning ranges from 1.7 to 3.131Hz, 3.0 to 5.6 MHz, 5.0 to 12 MHz and 11.5 to 31 MHz. A Zener diode (D2) is used at Ql to lower the operating voltage of the oscillator. A small value capacitor is used at C5 to ensure light coupling to the tuned circuit. Q2 is a source-follower buffer stage. It helps to isolate the oscillator from the generator-output load. The source of Q2 is broadly tuned by means of RFC1......

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This circuit will operate with fundamental-mode crystals in the range of 1 MHz to 20 MHz. Feedback is controlled by capacitor voltage divider C2/C3..

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This circuit operates 30-200 ppm above series resonance. Physically simple, but analytically complex..

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Figure 1, below, shows the 10.58 to 10.74 MHz VFO oscillator circuit. Yes, this is the same circuit that was presented last time, but Ive re-drawn it to show the Colpitts oscillator more clearly. "L" is approximately 1.5 uH; 19 turns in a T50-6 core (yellow). The value of C6 is found experimentally. I used 69 pF (a 47 pF and a 22 pF in parallel). More about this during check-out...

Its frequency depends on the capacitance of the vary cap diode. The center frequency is changed by varying the biasing voltage of the vary cap through the 47K pot. You can use a 75cm telescopic antenna or simply a length of hook-up wire. Mine worked fine with a 6cm hook-up wire and gave a range of 100m with a good FM receiver...

Its frequency depends on the capacitance of the vary cap diode. The center frequency is changed by varying the biasing voltage of the vary cap through the 47K pot. You can use a 75cm telescopic antenna or simply a length of hook-up wire. Mine worked fine with a 6cm hook-up wire and gave a range of 100m with a good FM receiver...

It uses 22 each 2N2222`s and will run from 12 Volts. The Receiver is a direct-conversion design with a switchable input attenuator and RF preamp, diode balanced mixer (diodes were allowed), a switchable low-pass-band-pass passive filter, and audio amplifier. (I may replace the audio final with the version presented by K8IQY, which I like much better). The Local Oscillator also serves as the VFO during transmit. The oscillator is a Colpitts design with varactor tuning, and.....

The circuit uses two CMOS IC’s IC1 uses inverters connected as a Colpitts oscillator of 100KHz; the LC frequency determining elements being the search coil and parallel resonating capacitor. An 80 turn close wound 30swg 100mm diameter coil will fit inside the CD case. I will leave the choice of the IC to the reader: this can be any of the well known CMOS inverters or NAND, NOR gates etc configured as an inverters. The choice is yours, use whatever you have on hand......

Views: 2743 | Votes: 51 | Comments: 0 | Rating: 1 | Rank: 2 | Added: Dec 24, 2012 |

Yes, this is the same circuit that was presented last time, but Ive re-drawn it to show the Colpitts oscillator more clearly. "L" is approximately 1.5 uH; 19 turns in a T50-6 core (yellow). The value of C6 is found experimentally. I used 69 pF (a 47 pF and a 22 pF in parallel). More about this during check-out...

My version is a 40 Meter CW/DSB (Double-Side-Band) Transeciver. It uses 22 each 2N2222`s and will run from 12 Volts. The Receiver is a direct-conversion design with a switchable input attenuator and RF preamp, diode balanced mixer (diodes were allowed), a switchable low-pass-band-pass passive filter, and audio amplifier. (I may replace the audio final with the version presented by K8IQY, which I like much better). The Local Oscillator also serves as the VFO during.....

Views: 4532 | Votes: 61 | Comments: 0 | Rating: 5 | Rank: 3 | Added: Nov 6, 2012 |

A squegging oscillator is an elegant two-for-one solution to the problem. Figure 1 shows how simple it can be. If you have studied for your Extra Class ticket, you`ll remember that a Hartley oscillator has a tapped inductor that provides feedback to sustain oscillation. (And if you took your test 25 years ago as I did, you`ll remember having to do freehand drawings of Hartley and Colpitts oscillators as part of the test!) L1 and L2 form the tapped inductor in this case......

This circuit provides an FM modulated signal with an output power of around 500mW. The input Mic preamp is built around a couple of 2N3904 transistors, audio gain limited by the 5k preset. The oscillator is a colpitts stage, frequency of oscillation governed by the tank circuit made from two 5pF capacitors and the inductor. ( Click here for Colpitt Oscillator Resonant Frequency Equation.) Frequency is around 100Mhz with values shown...

This is an image Schematic. No Description available...

This circuit provides an FM modulated signal with an output power of around 500mW. The input Mic preamp is built around a couple of 2N3904 transistors, audio gain limited by the 5k preset. The oscillator is a colpitts stage, frequency of oscillation governed by the tank circuit made from two 5pF capacitors and the inductor. ( Click here for Colpitt Oscillator Resonant Frequency Equation.) Frequency is around 100Mhz with values shown...

Views: 797 | Votes: 46 | Comments: 0 | Rating: 8 | Rank: 3 | Added: Jun 27, 2012 |

The Colpitts Oscillator is characterised by tapping the mid-point of the capacitive side of the oscillator section. The inductor can be the primary side of a speaker transformer. The feedback comes via the inductor. ..

Simplified circuit diagram of the two-stage Colpitts oscillator. In comparison with the classical single-transistor Colpitts oscillator [1,2,5] the two-stage modification includes an extra transistor Q2 and an extra capacitor C3. We note that both transistors, Q1 and Q2 in respect of AC signals are in a common-base configuration...

Modern set-top DBS TV tuners require high performance, broadband voltage control oscillator (VCO) designs at a competitive cost.To meet these goals, design engineers are challenged to create high performance, low-cost VCOs...