LF: Re: Fwd: Help needed, mechanical filters

["Clemens Paul" <cpaul@gmx.net>]

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 -----

From: Stefan Schäfer

To: rsgb_lf_group@blacksheep.org

Sent: Friday, June 29, 2012 10:26 PM

Subject: LF: Fwd: Help needed, mechanical filters

4th try...

-------- Original-Nachricht --------

Betreff:	Help needed, mechanical filters
Datum:	Fri, 29 Jun 2012 20:58:41 +0200
Von:	Stefan Schäfer <schaefer@iup.uni-heidelberg.de>
An:	rsgb_lf_group@blacksheep.org

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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