Monday, November 08, 2010

VHF FM transmiter using the Si570 (21.4 IF)

Here's the schematic for the new VHF FM transmitter. it's not production grade so please don't try to build this unless you know what you are doing and have an interest in share improvements. With different output filter and amp (none at the moment) I am sure this could be made in to an 10m to 2m FM transmitter, the only limit being the Si570 output frequency capability.

I have to find a 21.4Mhz filter for future testing. Audio is nice but can always be improved. In my prototype both ampop's adjust trim pot are at mid scale.
The core in the coil connecting the NE602 input is a red one (first one if found in the box) and there's no core at the oscillator tuned circuit, just air and near coupling.
Ceramic 10.7Mhz resonator is from one of those cheap AM/FM radios. A crystal would not work nice (to low capacity in the varicaps?) and also tested with negative result with an normal ceramic filter at the earlier prototype stage.

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