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CK-3V FM Transmitter - Circuit design (added 02/05) |
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Components of a simple Hartley Oscillator - (electronic Circuit / Schematic
(added 02/05) |
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Design & Construction of Radio Frequency (RF) Oscillators - Circuit design (added
02/05) |
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Electronic Canary - This circuit is a modified hartley oscillator with a couple of
extra components included. The transformer is a small audio transformer, type LT700.
The primary is center tapped with an impedance of 1Kohms at 1KHz . The secondary has
an impedance of 8 ohms. The inclusion of R1 and C1 give this oscillator its
characteristic "chirp". As the 100u capacitor charges via the 4.7K resistor, R1 the
bias for the transistor is cut off. This causes the oscillation to stop, the capacitor
discharges through the base emitter circuit of the transistor and oscillations start
again. Altering these components alters the frequency of the chirp. The chirp is also
voltage dependent. When the push button switch is operated the 100u capacitor is
charged. When its released, the oscillation decays and the chirp becomes faster.
(added 02/05) |
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Hartley oscillator requires no coupled inductors - 10/26/06 EDN-Design Ideas:
Examine a traditional Hartley oscillator circuit, and you'll note its trademark: a
tapped inductor that determines the frequency of oscillation and provides
oscillation-sustaining feedback. Although you can easily calculate the total
inductance required for a given frequency, finding ....(design idea added 09/06) |
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I.F. Amplifier - The I.F. transformer primary has 18 turns, the secondary winding
has 4 turns. The capacitors across the IFT primaries are 82pF. The input/output
transformer has 12 turns, tapped at 3 turns from ground. This transformer is wound on
a ferrite core. The mosfets are 3SK45's. The diodes in the product detector are
1N34's. I use a six pole SSB filter from a scrap CB. The centre frequency is 7.8MHz.
The -6db bandwidth is about 2.5KHz. (added 02/05) |
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Resonator BFO Circuit - This circuit was used to stop all the BFO drift. The
circuit is extremely stable. Turn the receiver off, and then on at any time and
temperature, the BFO frequency is exactly the same. (added 02/05) |
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series regulator with Q900 - This is a series regulator with Q900 being the
control element, Q901 a driver, and Q902 an error amp. ZD900 forms the emitter
reference voltage source. Since the generated high voltage and other voltages are
linked by means of the magnetic field of T900, any change in H.V. will be reflected
back to all of the other voltages. (added 02/05) |
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Shortwave Audion - It is a Hartley-ECO Audion, in which the plate is grounded for
RF. Positive feedback from cathode to grid occurs via the coil tap. The amount of
feedback is determined by the 100k pot; this controls the voltage at the screen grid
and thereby the transconductance of the valve (higher voltage resulting in greater
transconductance). …(schematic added 06/07/08) |
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VFO/Buffer - It's basically a standard Hartley oscillator, followed by Roy
Lewallen's buffer (page 14.20 of the 2001 Handbook). Output is +7 dBm into 50 Ohms.
Don't be tempted to add a gate diode, this circuit doesn't need it, and it will
degrade the phase noise performance, according to Ulrich Rohde. It should be
suitable.... (added 02/05) |
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Was that Really a Wildlife Tag? - In wildlife management, very few tracking
transmitters send some form of "station identification." Radio tags for birds and
small mammals can't. These little devices must put out a signal to a ground range of a
mile or so for up to a year or more, yet weight only a few grams, including battery.
To do that, most of them....(added 02/05) |
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What I had to do to stabilize a VFO… - (electronic Circuit / Schematic
(added 02/05) |
