Thursday, July 01, 2010

VHF Preamplifier with BFR91

Decided to place a frontend preamplifier for my last VHF FM receiver (will post the receiver schematic in the future).

This time instead of using the commun BF981/961 typical amplifier I went to the BFR91 transistor. The BFR91 should be a little more noisier but hell, this is not for tropo or moon bounce, it's just for the local repeater... I didn't checked values but I am sure that for this components values it should be working in class A or near it....

The idea and main schematic is from "PA0NHC" (site is down at the moment so will not place here link), with the usual changes/"extra" component removal (some filtering on the power line):

The 1N4001 if from the main receiver power supply...see the post bellow on the 78XX regulator for a clear understanding on why it's placed there...

The finished product (the preamp is on the top left side).

Well it did improve the reception but will have to make some more tests to see how well it goes. At this time I placed no input filter, just using the output filter before the SBL-1.

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