Kees,
spur's frequency of ~23MHz ? The existing uBITX 20/17 LPF?IF USED ON 15m?actually is ~0.5dB down at 21.450MHz and the ~23.xxMHz spur is down ~6dB.?
Save for the built in filter (existing) is switched out at 21mhz and all that's left is the 33mhz low pass
as is.??
I don't think stretching the 20/17M filter to add 15m is going to be effective enough unless
it has a brick wall shape.? The attenuation would have to be under 1db at 21.45 and not
less than 25db down at 23.55.? That is a rather tall order.?
A tapped double tuned band pass with tuned top coupling between
resonators has a good chance of that.??
I assume this is for the amp input side as at the output side it worse.
Allison
