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Active Antenna With Gain |
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| The signal booster, built around
a few transistors and support components, offers an RF gain of about 12 to 18dB (from
about 100kHz 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 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 0.5 to 2.5 mH will do. The value of R2 sets the Q2 bias at about 2V. If the voltage is less than 2V, increase the value of R2 to 1.5k ohm. To go below 100kHz (to bottom of the RF spectrum), increase the value of C1 to 0.002uF. The antenna is short pull-up type (42" to 86" long). |
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