Wideband Active Antenna Circuit


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Süper Moderatör
A 30 to 50 cm whip antenna provides reception from 10 MHz to over 220 MHz. T1 BF981, a dual-gate MOSFET, provides low noise, high-input impedance and high gain. The circuit is powered via the coaxial cable used to connect the antenna to a receiver.

Wideband active antenna amplifier circuit​


Active Antenna with Gain​

The signal booster, built around a few transistors and support components, offers an RF gain of about 12 to 18 dB (from about 100 kHz to over 30 MHz).

The RF signal is direct-coupled from Q1's source terminal to the base of Q2, which is configured as a voltage amplifier. The output of Q2 is then direct-coupled to the base of Q3 (configured as an emitter-follower amplifier). Transistor Q3 is used to match and isolate the gain stage from the receiver's RF-input circuitry.

Inductor L1 is used to keep any power source noise from reaching the FET (Q1) and any value of RF choke from 0.5 to 2.5 mH will do. The value of R2 sets the Q2 bias at about 2 V. If the voltage is less than 2 V, increase the value of R2 to 1.5 kΩ. To go below 100 kHz (to the bottom of the RF spectrum), increase the value of C1 to 0.002 µF. The antenna is a short pull-up type (42" to 86" long).
UHF Antenna Amplifier (Booster)
This UHF antenna amplifier circuit or UHF antenna booster circuit can be used to amplify or boost the signal of UHF band from 400 MHz to 850 MHz. This circuit is using only single transistor and provides 15 db amplification. For best results keep all the leads of the components as short as possible and fit the
circuit in a water proof case and install it near antenna. Shield the transistor from other components. L1 and L2 are equal to 2 turns of 0.5mm enameled copper wire woud on 3mm former, both the coils are aircore. L3 and L4 are equal to 10uH HF choke or 0.2mm 10 turns on ferrite core.The current consumption of the circuit is between 5 to 15mA. To power the circuit the voltage is fed through the cable by using a choke coil so it will prevent the DC voltage from entering in to the TV.​