Hi Stefan,
>4th try...
That's the reason why I opted for for the
yahoo list...
But back on topic.:-)
If I understand you correctly you did not terminate
the filter output side while
measuring with the hi Z probe.
I would try the same measurement with a correct
termination.
As there are also 500Ohm taps available you
could either
feed with a series 500 Ohm resistor and terminate
the output by 500 Ohm
or the same arangement with 18k if you don't want
to use the 500Ohm taps.
The plot looks typcally for a crystal or mechanical
filter which has not been terminated
properly.
73
Clemens
DL4RAJ
----- Original Message -----
Sent: Friday, June 29, 2012 10:26
PM
Subject: LF: Fwd: Help needed, mechanical
filters
4th try...
-------- Original-Nachricht --------
MF,
I have bought a mechanical filter which has a center frequency of 473
kHz. It is available at
http://www.oppermann-electronic.de/html/body_hf-spezialbauteile.html
(scroll down to FZ 01 / FZ 02). I have both types and just measured the
frequency response. There is a data sheet as well which states the
impedances to be connected to the wires.
There is even a datasheet at
http://www.oppermann-electronic.de/assets/applets/FZ_01.pdf
All in all it looks very interesting and the slopes are really very
sharp. However there is a passband ripple of 10 dB which is very very
high. See the image:
https://dl.dropbox.com/u/19882028/MF/Mechanisches%20Filter%20473%20kHz.png
So what have i done wrong? Or is it that bad?
The input signal is connected on the left side between the red and green
wire. The output signal is taken from the right side on the red and
green wire too. It looks as if each side has a coil on the green and red
wire, with a tap at the yellow wire.
Helpful was this image from the web
http://www.amateurfunkmuseum.de/AFM_321b-Dateien/image006.jpg which
shows a similar filter. I have connected a resistor of 18 kOhm to the
output and a 500 Ohm resistor in series to the signal generator, as
stated in the datasheet. But the ripple does not change.
Any ideas or suggestions?
Guess for what i will need the filter! :-)
73, Stefan/DK7FC
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