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.

Thank you again and best regards
Paolo

"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

"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.

This receiver has a tube based PLL for the LO. This was completely off
on all bands due to the fact that all the cores of the Ls loosened,
they were kept firm with some sort of glue across the thread that
pulverized over the years. The vibrations of the drum did the rest.
After the alignment, it is now rock stable, better than the 8640!
However, I did not consider the IF filters when I did this, I tuned
the LO for *exactly* 3.3MHz IF that then become 300kHz after another
mixing with a fixed 3MHz quartz oscillator. It is not a good idea to
tweak this oscillator too, as it also generates the harmonics used by
the PLL. This is actually 3 to 5 Hertz off.

I am *very* worried of upsetting the filters. I like the idea of
identifying which trimmer changes which part of the curve before
attempting the real job and preparing a reference chart. I am
convinced that some previous owner tried the alignment before and not
necessarily did a terrible job. The manual just has charts with the
expected shapes of all six, the number of peaks, at which freq they
should be, the maximum ripple. The representation on the scope is
linear, I suspect it will not be accurate enough. Today I tried with
the digital scope, set the persistence to 10sec so that I can see a
curve produced by ten sweeps, this seems to be an improvement. Also,
-3dB=0.707x linear, the digital scope has cursors that also help.

Another thing I wanted to ask and you already mentioned: which filter
to start with? The narrowest, this one is easier to center at exactly
the right freq. You make a difference between "crystal" and "tunable",
however this thing must be quite odd, the crystal filter is also
tunable, has its own ten trimmers as the non-crystal types.

Thank you again for your help
Best regards
Paolo

"paolo67" wrote in message
...
This receiver has a tube based PLL for the LO. This was completely off
on all bands due to the fact that all the cores of the Ls loosened,
they were kept firm with some sort of glue across the thread that
pulverized over the years. The vibrations of the drum did the rest.
After the alignment, it is now rock stable, better than the 8640!
However, I did not consider the IF filters when I did this, I tuned
the LO for *exactly* 3.3MHz IF that then become 300kHz after another
mixing with a fixed 3MHz quartz oscillator. It is not a good idea to
tweak this oscillator too, as it also generates the harmonics used by
the PLL. This is actually 3 to 5 Hertz off.

I am *very* worried of upsetting the filters. I like the idea of
identifying which trimmer changes which part of the curve before
attempting the real job and preparing a reference chart. I am
convinced that some previous owner tried the alignment before and not
necessarily did a terrible job. The manual just has charts with the
expected shapes of all six, the number of peaks, at which freq they
should be, the maximum ripple. The representation on the scope is
linear, I suspect it will not be accurate enough. Today I tried with
the digital scope, set the persistence to 10sec so that I can see a
curve produced by ten sweeps, this seems to be an improvement. Also,
-3dB=0.707x linear, the digital scope has cursors that also help.

Another thing I wanted to ask and you already mentioned: which filter
to start with? The narrowest, this one is easier to center at exactly
the right freq. You make a difference between "crystal" and "tunable",
however this thing must be quite odd, the crystal filter is also
tunable, has its own ten trimmers as the non-crystal types.

Thank you again for your help
Best regards
Paolo

One of the biggest issues of a radio with variable selectivity and passband
tuning is figuring what is being tuned and how the IF and BFO might be
shifting and what oscillators are being shifted in and out for various
modes, then determine what filters are the least adjustable and see what
shape you can get from them. Typically the monolithic filters, be they
crystal, mechanical or ceramic can only be adjusted for input and output
matching.

PLL cores are adjusted so that the VCO can be reliably tuned across it's
range. The steering voltage is usually specified either at some frequency
or at the extremes.

Offset oscillators for various modes also need to be accounted for.

Transceivers are even more critical because you will wind up poor fidelity
and/or spurious. Loading changes can make a shift between transmit and
receive too. I can't figure out how the High Fidelity SSB guys deal with
phase noise and carrier rejections as they approach response below 200 Hz.
Especially the ones who do a base boost to try to get fidelity out of the
cheap 500-4000 Hz speakers in mobiles, but sound like a craphouse studio on
a good quality station speaker.

3-5 Hz is pretty good but it just makes it more noticeable when the hum on
the incoming signal is out of phase with the hum modulation in the receiver