--- In BITX20@..., Rob Frohne <frohro@w...> wrote:
Hi All,
I had some surplus 6 MHz crystals here, and so I'm using that as an
IF. If I use the 50 ohm termination impedance that Fahran has set
up, the filter ripple is more than 10 dB in the passband. (It should
be better with a 10 MHz IF.) If I can raise the termination
impedance it helps a lot on the ripple. It is harder to keep the
high frequency response with the higher impedances I'm trying to use
as well.
One possible solution is terminate the filter at 200ohms and use
a 4:1 balun at each end. That yeilds a 50ohm interface to the
amplifiers and allows a filter at a more reasonable impedence.
FYI: you may consider a 5:1 or even as high as 9:1 ferrite loaded
transformer as at 6mhz my experiments with filters for SSB passband
indicated a 400-500ohm termination was more redially achievable
and gave better shape factors with less ripple. The losses in the
transformers are small and can result in lower losses in the filter
at a more workable terminating impedence.
Allison
KB1GMX
