Electronic schematics, circuit designs
Radio field indicator with MOS-FET
A rf field indicator is required to verify power stages and transmitters antennas. With this radio field indicator you can measure radiated energy from antenna. This circuit is very sensitive, a weak signal is enough.
The S2 commutator allows to select : 480KHz … 2.4MHz / 2.4MHz … 12MHz / 12MHz … 40MHz.
A 30cm long wire is enough as a antenna.
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VN66AF 27MHz CB amplifier
The 10 meters 27MHz CW radio amplifier is equiped with VN66AF transistor produced by Siliconix wich has some advantages: its cheap, great dielectric insulation and high gain. Here we use VN66AF as an rf amplifier for 10m band (26 … 30 MHz ).
With this 27MHz rf amplifier, small transmitters ~ 200mW, can be transformed in 2 to 3 W 10m transmitters. The band-pass filter attenuates at least 55dB.
For linear applications (AM and BLU) the VMOS FET gate current has to be 20mA adjusted with P1. If we want to use this 10m rf amplifier for FM and CW adjust P1 so there is no current to FET gate. In our case the repose current ( steady current ) is 200mA to 300mA.
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Quatz oscillator
This quartz oscillator circuit has greater stability than a parallel resonance circuit. It generates frequencies up to 30 MHz or even higher if you use BFR 91 T1, T2 transistors and reduce R1 … R2 values. The MOSFET buffer insulate the oscillator from any connected circuit.
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