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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....
Hartley oscillator requires no coupled inductors - 26-Oct-06 Issue of EDN
Capacitive reactance replaces mutual inductance.… [Design Idea by Jim McLucas,
Longmont, CO; Edited by Brad Thompson and Fran Granville]
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)
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)
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)
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)
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)
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)
