On 2006-07-10, K7ITM wrote:
try putting this circuit into "RFSim99" (a free program)

Thanks, I'd been looking for something like that.

unloaded Q of the inductor there to see the effects on performance,
both loss and filter sharpness (-- rejection of unwanted signals).

I see. So the reason that the Q matters so much is not that it affects
the filter shape much (in this topology), but that it has a big effect
on the amplitude of the (tiny) passband which provides additional
separation from the unwanted signals. In this case it looks like
raising from Q=50 to 250 gives about 4dB of "wanted" signal without
really affecting anything else.

couple minutes, the simulation can give you some insights to get you
started and save a lot of time soldering, but expect to ultimately
learn even more by actually building and measuring the circuit.

I actually have such a circuit built, and I took some measurements
today. I'll wind a 1.8uH inductor on a T37-2 tonight and compare.

Thanks to all for the responses.

--
Ben Jackson AD7GD

http://www.ben.com/