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More than Circuit EngineeringNonselective Amplifiers
Ñõåìû >> Antenna Equipments >> Nonselective AmplifiersNonselective Amplifiers
To increase amplification of
antenna it is needed to multiply the quantity
of directors, but frequency
band is narrow. Tuned amplifiers has high
amplification factor, but they are narrow base-band. The use of nonselective
amplifiers on transistors enables to multiply an
amplification factor on 10 - 12 dB on one cascade.
On pic.1 represented circuit of
one-stage amplifier on the transistor 2T372A, lower
frequency 45 MHz (beginning with the first TV channel), where L1 - 10 turns
winded by a wire ÏÝÂ - 0.8 on framework diameter 5 mm, L2 - 30...40 turns
winded by a wire ÏÝÂ - 0.2 on a ferrite ring
diameter 4 mm. Diode D1 - ÊÄ512,
condensers KM - 5. Amplifier powered by TV cable. Input impedance is 75
Ohm. Amplification factor 10 dB. Making the nonselective amplifiers it is
necessary to stick to the requirements of the high-frequency circuit wiring.
Pic. 1. One-stage Nonselective Amplifier
Circuit.
Pic. 2. Two-stage
Nonselective Amplifier Circuit (with Minus Power Supply).
Pic. 3. Two-stage
Nonselective Amplifier Circuit (with Plus Power Supply).
Circuit on pic.3 has similar descriptions as previous, amplification factor - 20 dB in wide frequency band. Circuit powered from plus voltage. Filter L1C1C2 in the input of amplifier reduce low-frequency less than 45 MHz.
Transistors: T1 - 2T372A, T2 - 2T372B; L1 - 10 turns, winded by a wire ÏÝÂ - 0.8 on framework diameter 5 mm, power supply filter L2 - 30...40 turns, winded by a wire ÏÝÂ - 0.2 on a ferrite ring diameter 4 mm.
Increasing amplification factor through increase of cascades is not effective, because stray coupling led to the narrowing of frequency band. To avoid this fact you need to braid cascades between itself.
added 18.07.07 01:04:30 | 
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