2m & 70cm PREAMPS for Satellite work (ON6UG design)

Here are some hints and tips for construction of a good preamp for satellite work.

It's main characteristics are :

BF998 / Silicon N-channel dual-gate MOS-FET transistor (download specs here)
high gain
excellent stability
low noise (< 1 dB)
immunity to high signal levels, and especially to cross-band signals (70cm), allowing full duplex
no-tune design (wide band input circuit and transformer-coupled output
2m version is detailed here, but 70cm is possible as well

Construction

Download the PDF here for detailed construction notes. the PCB is designed to fit in a GREENPAR inline box (or RS-components reference 456-201).

To check (adjust) the bandstop filter, I used a wideband noise source and observed the results.

(Click on any picture to zoom)

	The compact inline housing with BNC in/out - it is not waterproof. I have used to power the unit with a feedthrough capacitor instead of coax.
	The box conveniently opens by removing only one screw. View on the PCB with SMD components (the BF998 is as well a SMD) The input coil is mounted under the PCB.
	The PREAMP is of wideband design. Please note that for certain applications, a narrow band design would be more desirable. Be sure that the preamp is not overloaded by nearby FM broadcast or utility VHF-signals etc The actual performances: +20 dB on 145 Mhz > -40 dB on 430-440 MHz (stopband) 1 dB compression point : -15dBm on input S11 not very good (SWR on input=18:1), S21 is excellent (SWR on output < 1.1) !