Christoph PetermannHomepage

 432 MHz Low Noise Preamplifier for Moonbounce Operation and Weak Signal Reception

by Christoph Petermann DF9CY, 7 July 1999


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.

Schematic Diagram

Schematic diagram of the 432 MHz LNA


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)

432 MHz LNA

The innermost of my prototype of the 432 MHz LNA. You see a further diode to avoid damage by wrong polarisation.

Build up

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.

Redesign for 144 MHz

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.

Redesign for 220 MHz

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

GO (back) and visit my homepage