FET ภาคดูด มาแล้วจ้า หายากมากกกกกกกกกกกกกก อาทิตย์หน้าจ้า...........มีไม่เยอะนะครับใครที่จะทำบูสภาคดูดเตรียมไว้เลย I have an old VHF transceiver a little-bit "deaf"! By adding the following VHF pre-amp as 1st stage, the improving of sensitivity is spectacular. The pre-amp including also a Band-Pass input filter which rejects any undesirable signal outside of 2 m. Band.
I had worked manytimes MIR Space Station (good old days!) and ISS nowadays, with this circuit as antenna pre-amp and a simple 4 Elements HomeBrew VHF Yagi, always with excellent results.
I'm using also that as Antenna pre-amp for LEO Satellites (Mode-B), where the DownLink is into the VHF Band (145.9 - 146.00 MHz).
Part List
FET = BF988 , BF981
CT = trimmers 4-20 pF (Good Quality)
R1 = 82 K / 0.25 W (carbon)
R2 = 56 K / 0.25 W (carbon)
R3 = see text
R4, R6 & R5 = see Table below
R7 = 100 Ohm / 0.25 W (carbon)
C1 - C2 - C4 - C6 = 1nF SMD (or Trapezoidal-Ceramic)
C3 = 1nF / 63 V SM or ceramic
C5 = 10 uF / 16 V
C7 = 1nF (Feedthrough capacitor)
DZ = 10V / 1W Zener diode
L1 (air coil) = 6 turns, 1mm Silvered wire, length= 11 mm,
TAP. 1 1/2 turn from GND (cool-end), internal diam. = 6.3 mm
L2 = like L1 without TAP
L3 (air coil) = 5 turns, 1 mm Silvered wire, length 9 mm,
TAP. 1 1/4 turn from +VCC, internal diam.= 6.3 mm
