I intended to order some BC549 transistors, but ordered BC548 by mistake. As shown in the following table, the BC549 has a lower noise figure than the BC548; otherwise, they are interchangeable. I have three questions.

1. Is production simply sorted in order to determine which transistors are marked as BC548 versus BC549?
2. Is there a test that I can perform to sort the BC548s that I have in order to select those with the lowest noise?
3. Does the noise figure matter in the schematic linked here?

http://sound.westhost.com/project54.htm

Thanks.

 

There is a lot going on with FM transmissions. The quality difference will be barely detectable. You will be best off making the circuit and, if you actually get it to work and are happy with it, you are done. If you get the oscillation to work and can receive in FM and are still not happy, you can try a different antenna (broadcast & receive), different frequency for broadcast and finally different transistors.

I would just start building it, see if it works and then move on. Don't get caught up in the details or perfection yet.

 

Why worry about noise from the transistors when the input signal must be amplified?
The TL061 preamp shown produces much more noise than the transistors.
The preamp should be a low noise opamp.