Low noise amplifier (preamp)

Page under construction...


Board size is 39mm X 32mm

At the moment available PCB or PCB with NE42484A

A simple, Inexpensive, small and easy to bulid "source bias" preamp/ small signal amplifier, etched on FR4 for the lower bands (ie VHF,UHF) Designed to be versitile it can be "moded" to suit.


As a LNA (using Microwave style devices)
This board was originally designed around the NE42484A (super low noise) HJFET but most similar fets will work just as well.
So far Ive had the board producing very good gain on 6M, 2M and 70cm   (ive even had it producing  >10db @ 10ghz! but this is not recomended.)

The Input match is designed around Noise Figure (less gain).  The parallel combination of C2-L1 can have a very good (High Q) bandpass response. The best tuning of C3 is not always obvious ( Best gain is usually not the best noise figure!!)
experimentation is needed to suit required results.

I have no way of measuring Noise figure but im fairly confident that it would be very low if tuned correctly.

Stabitity is CONDITIONAL. As most are aware these devices have a lot of gain on the lower frequencies and are very difficult to tame! Ive got it fairly good but a reasonably good load (antenna) is still needed on the input. (work in progress)

Note: A small value capacitor (2-4pf) on the output of the device has seemed to eliminate all stability issues, without affecting noise figure. (now unconditionally stable) 





Please follow the Layout Carefully!

So far,


For The NE42484A HJFET

6M Band
More than 18db of gain is available.
C1 22pf
C2 1nf
C3 130pf (a 0805 capacitor can be placed in parrallel with the trimmer)(If gain is peaked at 49Mhz, noise figure on 50 (6M) should be close to optimum)
L1 68nh

2M Band
More than 18db of gain is available.
C1 7.4pf
C2 330pf
C3 around 12pf (trimmer) (If gain is peaked at 139Mhz, noise figure on 144 (2m) should be close to optimum)
L1 68nh

70cm Band
More than 18db of gain is available.
C1 2.4pf
C2 100pf
C3 around 11.6pf (trimmer) (If gain is peaked at 425Mhz, noise figure on 432 (70cm) should be close to optimum)
L1 10nh
 

ATF36077 (not tried yet ( calculated values))

2M Band
C1 2.8pf
C2 330pf
C3 14.7pf (trimmer)
L1  68nh


More to come!