Re: LF: RE: Fwd: Help needed, mechanical filters

[Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>]

MF,

It becomes better!

I just realised that this filter is perfect to protect a receiver like the IC706 when using a BIG antenna as the MF receive antenna. It will be easy to build a passive circuit out of a transformer 50 Ohm -> 18 kOhm -->Filter--> 18 kOhm -> 50 Ohm. This can be put in a small box and then there will be no problems! I remember how the 706 and others behave on long wires, i.e. multi-band antennas...

73, Stefan

Am 29.06.2012 23:03, schrieb Mike:

Stefan

Have you included the 300pF capacitor (I do not read German) and not sure if it is the same on both ends?

I would expect the launch circuit needs a cap both ends.

Mike G3JVL

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of Stefan Schäfer
Sent: 29 June 2012 21:27
To: rsgb_lf_group@blacksheep.org
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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