de 4N1ZM
I was looking in different designs of ssb trx and it looks like that
most important part is exactly filter. And that is place where
successful work of trx can easy fail. Crystals are simply different
from producer to producer from lot to lot. Without measuring to get
good filter is more lottery than predictable result. Only in
situation that somebody can use the same type of crystals producer
and batch results might be comparable.
One other approach is Kohn type filter with all same capacitance
values that can be trimmed by variable c or varicaps in the section.
That one looks most permissible and easy try without much work.
Here is link to collection of all ladder filter approaches:
You should fist get djvu viewer from
By the way djvu format is the most efficient for schematics size on
the net, even in comparison to pdf.
--- In BITX20@..., "Max" <m_orwell@y...> wrote:
de 4N1ZM
There is two programs and alternative aproach to ladder filter
design.
Since altavista translation can overcame language bariers it is
possible to check this link through systran translation engine.
Program give obvious relation between impedance capacitance and
crystal unit mesurmen tools:
--- In BITX20@..., "ajparent1" <kb1gmx@a...> wrote:
That is a good starting point but I'd add much has been published
since then on building crystal filters.
Using the series ladder design and the right constants you can
build
USB and LSB filters as well as symetrical. A good source is the
ARRL
publication Experimental Methods in RF Design which devotes a
fair
amount of text to crystal filters and has a good listing of
citings
for further reference.
I've use their techniques to build excellent filters using 6 and
8
crystals with symetrical shapes to greater than 70db and low
ripple.
The gausian to 6db shape happens to sound the best to me for
2.2khz
SSB filters. I'm using a 6 crystal version of same in the first
version of BITx I've built as an transverter IF.
Allison
KB1GMX
