Dome Filter Question

[Martin Czech]

> Hi,
> 
> I wonder if anyone can tell me if is possible to replace the presets in the
> Bode Dome Filter with fixed resistors and if so what values should be used?
> 
> Also, would it be better to replace the transistors with opamp stages?
> 
> Available from:
> http://aupe.phys.andrews.edu/diy_archive/manuals/moog/mod_50.gif
> 
> Thanks in advance.
> 
> Steve Cook.
> 
I wonder if there is no better circuit...
As far as I understand, the "dome filter" is two allpass which have a
allmost constant phase shift of 90 deg between them, in order to get
large bandwidth quadrature.

I found such a filter in an old amateur radio book, they need SSB as
well. It is a passive RC ladder with four signal ways. You need a trafo
or op amp phase splitter in the front end (180 deg). I can remember
that a simulation showed < 0.5 deg error for a capacitor ratio of 1.6.
That is a lot of capacitors, and you need 4 matching for each stage.
OTOH, the more stages, the less matching is needed.
I know somebody who made his SSB reciever with this "polyphase" method.
If someone is interested, I could dig this out. It would
even be better if you could provide some web space as well...

m.c.