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50 MHz high dynamic and low noise RF preamplifier

by IK0VAQ - Alessandro



The preamplifier I’m describing is used as external device and drives a signal splitter for a secondary spectrum receiver (eg. Panadapter, SDR receiver etc). The performance of the device adopted, the Minicircuits PGA103+ Monolithic Amplifier, are very interesting mainly for the high dynamic range. The very low noise is not a big issue on Six Meters band but is still a good thing to have.

The overall gain, included the 6 dB attenuator on output, is equal to 20 dB with a NF on 1,5 dB (0,5 dB of PGA103+ plus 1dB of input filter loss).

Only one reported problem could be found using the PGA103+: strange device failure without apparent reason. Minicircuits has published the technical note AN-60-064 describing a possible instability of the device under 100 MHz frequency, this could cause the PGA103+ failure. The cure is the adoption of a stabilization network described in the same technical note L3, C1 and R1 (thanks to Marco IW0FFK). After some month of use no any failure has been occurred.

The schematic is very simple and the picture can explain mine build; the high current absorption needs to put an heat sink on the stabilizer IC 7805 and solder the ground tap PGA103+ on the copper plate with a good quantity of tin to dissipate the heat.

Thanks to Marco IW0FFK for the device suggestion and technical note mailing.




Picture and schematic diagram





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