Hi All
I'm trying to use TQF9-02 (similar to xf9b)(impedance 500ohm) filter in
receiver on MC3362.
In original project there was homebrew filter connected to pins 17,19
MC3362 via capacitors 220pf.

Have you any ideas for proper termination of Xfilter?

MAc

MAc wrote:
Hi All
I'm trying to use TQF9-02 (similar to xf9b)(impedance 500ohm) filter in
receiver on MC3362.
In original project there was homebrew filter connected to pins 17,19
MC3362 via capacitors 220pf.

Have you any ideas for proper termination of Xfilter?

MAc

Andy writes:

If the specified filter termination impedance is 500 ohms, you have
to take the 3362 input impedance and transform it to 500 ohms.
I don't know the 3362 input Z, and am too lazy to look it up, but most
likely it is higher than 500 ohms and has a capacitive component...
So, use math to find out what the parallel R and C is, and things
will start to make sense...

Lots of ways to do this, but ALWAYS use a tuned circuit. Otherwise
you will have a reactive component that will mess you up...

Personally, I like to use an inductor and two capacitors, since it
provides DC blocking. Some people like transformers......

Andy in Eureka, Texas

PS Rp = Rs (1 + Qsquared )\

Xp = Xs ( 1 + Qsquared) / (Qsquared)

Q = Rp / Xp or Q = Xs / Rs

If you put these in a Basic program, and learn to use them, it
makes things a lot quicker....

I only found (app note), that filter should be 330ohm

Depending on the bandwidth of the filter, typically, the natural impedance
of the filter will be anywhere in the range from 1.5k to 7k. Using ECS
10.7MHz crystal filters as an example, the 50kHz filter has an impedance of
around 6.5k, while the 25kHz filter has an impedance of around 3k.
Most crystal filter don't have a low impedance, but there are exceptions.
The 330 ohm impedance that you describe is typical of the Murata 10.7MHz
ceramic filters. An example would be the SFE10.7V, with a 13kHz bandwidth.
The skirt selectivity on these types of filters is very poor, so about the
only use that they really have is as a roofing filter at the 1st I.F. of a
dual-conversion receiver.

Pete

"MAc" wrote in message
...
I only found (app note), that filter should be 330ohm