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LF: Re: Fwd: Help needed, mechanical filters

To: <[email protected]>
Subject: LF: Re: Fwd: Help needed, mechanical filters
From: "Alan Melia" <[email protected]>
Date: Fri, 29 Jun 2012 23:08:08 +0100
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Stefan if they are really that old then they mar be deterioration of the elements. I remember the Kokusai fikters used in KW TX and RX designs (much bigger profile) degraded over the years. I have a few of those type of filters, my measurements suggest that ripple was not an important aspect (perticularly if they were for NBFM. However they look more like AM filters .....Mikes idea is good I found that the best shape is not always with the specified termination. PMR makers are more interested in adjacent channel suppression than in-band linearity. A lower termination impedance will flatten the response but also reduce the out-of-band attenuation, and probably the slope, and increase the insertion loss. They can be cascaded .....gain is cheap at those frequencies.
 
Alan G3NYK
 
----- Original Message -----
Sent: Friday, June 29, 2012 9:26 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 <[email protected]>
An: [email protected]


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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