infra-red controlled remote switch

Nowadays, several manufacturers produce ICs that combine an infra-red receive LED with associated amplifier and demodulator. The type SFH505A from Simens used in present circuit has, in addition, a band-pass filter to minimize any interface. It is best used in conjunction with an infrared transmitter in the next article. The output of IC1  is limited to a[…]

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Infra-red transmitter

Infra-red transmitter: It often happens that someone wants to watch television without the sound disturbing other people in the room. To avoid having a long cable trailing over the floor, the present transmitter (and accompanying receiver ) make it possible to listen to the TV sound wirelessly. The transmitter uses pulse-duration (=pulse-width) modulation. The modulated[…]

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Infra-red headphone receiver

Infra-red headphone receiver: This receiver is meant to complement the transmitter describe in the previous article. Its design is based on just one FET. This has the advantage that construction is simplicity ‘itself, and the disadvantage that for a sufficiently low output impedance the value of drain resistor R3 has to be fairly low. That results with[…]

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Miniature crystal oscillator

Miniature crystal oscillator: Nowadays, with the advent of SMT (surface mount technology), it is possible to construct tiny circuits. In the case of crystal oscillators, however, this may not always be feasible because of the size of the crystal. Fortunately, Statek, a specialist crystal manufacturer, produces crystals measuring only 8x4x1 mm for SMT. Together with[…]

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CB-to-SW down converter

This converter enables long distance (DX) reception of AM or SSB stations in the 27-MHz citizens’ band (CB) on a short-wave or medium-Wave radio (note, though, that AM or SSB modulation in the 27-MHz CB band is no longer allowed in a number of countries). The converter consists of a prestage, T1, and a mixer/oscillator,[…]

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S-meter for short-wave receivers

Some radio amateurs are very keen on accurate RST reports, others (mostly the VHF/UHF fraternity) never look at the S-meter on the receiver, and are satisfied as long as they can hear the other station. This circuit is the first group. Traditionally, one S-point corresponds to a 6-dB increase in signal strength, while ‘S9’ is[…]

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