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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Field-strength meter

Field-strength meter: The unit discussed here indicates, by means of a chain of LEDs, in logarithmetic ratios the strength of an electric field surrounding the unit. The inputs signal across the conducting discs is applied to the non-inverting input of IC1. The amplification of IC1, A = R4/P1. In the prototype, P1 was set at[…]

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CGA-SCART adaptor

The adaptor has the great advantages of not needing a separate power supply and requiring so few external components that these can easily be accommodated in the SCART connector. The signals on the R, G, and B pins of the CGA card are converted from TTL level to SCAM’ level with the aid of transistors[…]

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Low power NBFM transmitter

The transmitter is a crystal-con-12 trolled, battery-powered, one-chip narrowband frequency modulation v(NBFM) model for operation in the 27- m band, primarily as a wireless microphone*. The circuit is an application of Motorola’s MC2833 single-chip VHF narrowband FM transmitter IC, designed to work in the 27-MHz band. The transmitter output power is about 10 mW (+10[…]

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