"Lynn" wrote in message
...

"paolo67" wrote in message
...
Actually there is a row in the manual that says that after the
alignment the gain of the filter stage must be 30dB consistently on
all the positions, 40dB with zero bias. It is written in German and I
missed that row before. I will try to figure out what this means in
terms of IF output level.

1sec comes from 0.1sec per division by ten divisions. If I'm getting
it right, I should try to keep the gain as constant as possible for
the purpose of the alignment, this is the key point I missed before.

The fact is that, at the moment, with either AGC off or AGC on, the
filters are quite far from spec, sometimes the center freq is off,
sometimes the top is not flat and/or the width is twice or three times
than expected. There are ten trimmers per filter, sixty total.

Tomorrow, I will record the current conditions and try to make some
progress.

Wow, sounds like trying to do an old tube type TV IF alignment.
One can't just start tweaking each trimmer for maximum smoke,
of course. You've got to decide just which skirt of the filter's bandpass
shape each trimmer is supposed to be working on. If the manufacturer
doesn't tell exactly where each trimmer is supposed to be working,
it might be well to make a little chart of where you think each trimmer
should be working, and keep good notes of where you are going.
If someone hasn't already "aligned" it by "ear", you can usually
detect where each trimmer is working by twiddling it just a very little,
back and forth, while carefully watching the shape on the scope.
They normally will not drift off so far by themselves that you can't see
and watch just what you are doing, and where each trimmer was working.
Just keep cool, and don't make any giant moves until you can see
where you are going with each step along the way.
Also, keep in mind that the manufacturer's filter bandpass specs
were often pretty optimistic!
Old Chief Lynn, W7LTQ

Typically, Low IF shouldn't be aligned unless someone tweaked it or you had
to fix something. First sweep the Crystal filters and find the center of
those before going on to the tunable filter. These are not always perfect
or centered and you may find want to adjust the LO or tunable filters
slightly off to compensate. I like the idea of rocking an adjustment to see
what happens, as this can reveal where the problem is without upsetting the
whole alignment.