This is a 137 MHz preamplifier I designed using a piece of an Amplifier schematic and a band pass filter. It is the result of a lot of experiment, I tryed other complicated configurations but I got ever strange behaviors or oscillations. At the end, I got the better performance using the simplest solution: a filter followed by a BJT in common emitter configuration.
This preamplifier is very simple to assembly, I used a teko 371 steel sheet box to have a strong shielding and it doesn’t require too exotic components, just remember to mount the 2 inductors of the input filter orthogonal each other. The center frequency tuning can be archived streatching a bit the input filter coils and adjusting the variable capacitor.
A cheap noise generator is useful to get the the characteristic of the amplifier, I don’t explain how I did it, just follow this tutorial. The following image show the preamplifier characteristic after the tuning.
Due to my poor equipment, I can’t give right numbers, the gain is approximately 15 db, however I took the longest image ever from NOAA 18. This image was obtained capturing the satellite data from 2 degree North to 2 degree South elevation.
Luigi Findanno Makes 