432 MHz Low Noise Preamplifier for Moonbounce Operation and Weak Signal Reception
Moonbounce is the most challenging field in Amateur Radio. Everything must be designed for to provide an optimum performance. A very low noise preamplifier as described here is an essential must. It is easy and also cheap to build a very good one without spending a fortune for a commercial type.
This Low-Noise preamplifier is a straight-forward concept using a widely available Mitsubishi Gallium-Arsenide Fet MGF1302. It will work with almost any similar transistor. You may get a better or a worse noise figure by changing to another GaAs Fet. The achieved power gain is around 16 dB and the corresponding Noise Figure F measured with 0.41 dB on a calibrated HP8970B + HP346A Noise Figure Meter. An adaption for other frequencies like 144 MHz and 220 MHz is easy and requires a different coil dimensioning only.
C4 = Hi-Q 0.3 .. 2 pF Tekelec-Airtronic or Johanson C3 = Hi-Q 0.7 .. 10 pF Tekelec-Airtronic or Johanson C1, C2, C6 = 1nF low inductance bypass capacitors C5, C8 = 1nF feedthrough capacitors C7 = 100nF diode noise reduction R2 = 120 Ohm 1/2 Watt R1 = 82 .. 120 Ohm ; adjust for ca 10 mA of Id current T1 = 4:4 turn of 0.1 mm Cu-wire on ferrite bead bifilar wound Q1 = Mitsubishi MGF1302 or similar GaAs Fet D1 = 5.1V Zenerdiode D2 = 1N4148 "security diode" L1 = 1-1/2 turn of 2 mm silvercoated CuAg wire of 6 mm inner diameter (see image) sockets = N-type high quality box = heavy tinned (and eventually silver coated) box (83*50*25 mm)
See the image, how I did the inner construction. Make the rf relevant leads as short as possible.
You have to use a noise figure meter. Check the voltages and the current. By carefully turning C4 and C3 tune the amplifier to the lowest possible noise figure. C4 has a "tendency" to the low capacitance side. My 3 examples are 0.40 dB, 0.41 dB and 0.37 dB.
I used this preamplifier in my moonbounce system with good success. It is cascaded by a second amplifier of the same type to overcome the cable losses. You will find images of the moonbounce system on another place on this site.
I have a design for 144 MHz which equals this 432 MHz amplifier exactly. The only difference is, that this heavy duty coil must have 5 .. 6 turns of the same wire and 6 mm inner diameter.
I tried one 220 MHz preamplifier. The heavy duty coil must have 3 turns of the same wire and 6 mm inner diameter.
Have fun and 73
Text and All Images are Copyright by Christoph Petermann DF9CY
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