Hi Ken,

My thoughts,

Am 16.09.2012 22:07, schrieb Ken:

Hi Stefan.
Thank you for all the filter info, definitely interested in them, at present
for 500kHz I have a homebrew filter using two Toko transformers in between
the antenna socket and two stage rx pre-amp.

What RX are you using? And what type of antenna?

  There are GE protection diodes
across the input,

I should think about that too. 3x Si diodes in series, 2x, antiparallel.

  the pre-amp gain is 0 - 18dB with a variable capacitor to
peak at the operating frequency.

What is the BW of that peak?

  I was thinking of replacing the 500kHz
filter with this mechanical one, it would save work, just need an input
matching Xformer and change the gate resistor on the input FET.

73, Stefan/DK7FC

Your thoughts please Stefan.

73.

Ken

M0KHW

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Stefan Schäfer
Sent: 15 September 2012 01:07
To: [email protected]
Subject: Re: LF: Re: RE: MF tonite

Hi Ken,

I just tried to use the 500 Ohm input and the 18k Ohm output. It works
UFB but then i got worried about destroying the filter due to the
up-transformation on the input (the max. input voltage is 2 V rms). Thus
i decided to rebuilt the circuit as it has been before and will
eventually use an uptransformer behind the filter. But probably this is
not necessary because the MF noisef floor is still 20 dB above my
RX+soundcard noise floor...

After readjusting the C, now the passband ripple is<  0.5 dB.

This is the schematic:
https://dl.dropbox.com/u/19882028/MF/MF%20Filter%20schematic.png
(You know, someone has done it all before and it is nothing new ;-) ).

Will you order and use some of them?

73, Stefan/DK7FC

Am 13.09.2012 21:47, schrieb Ken:

Hi Stefan.
Fully understand.

73.
Ken.
M0KHW

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Stefan Schäfer
Sent: 13 September 2012 20:03
To: [email protected]
Subject: Re: LF: Re: RE: MF tonite

Hi Ken,

OK but later. I want to try some modifications, i.e. using the 500 Ohm
input and the 18 kOhm output, to have some gain. If this does not affect
the matching, i would prefer that...

73, Stefan
Am 13.09.2012 20:43, schrieb Ken:

Stefan.
Thank you for the info, maybe sometime you will be able to post the

circuit?

73.

Ken

M0KHW

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Stefan Schäfer
Sent: 13 September 2012 12:26
To: [email protected]
Subject: Re: LF: Re: RE: MF tonite

Ah yes, Thomas was faster, damn ;-)

Another image from the experimental setup, using source followers

https://dl.dropbox.com/u/19882028/MF/Mechanical_filter_with_source-followers

.JPG
The results have been very good last night!

73, Stefan/DK7FC


Am 13.09.2012 13:12, schrieb Thomas Rosenkranz:

Hy Ken,

the name of the mechanical filter is FZ02
http://www.oppermann-electronic.de/html/hf-spezialbauteile.html

http://dm4tr.bplaced.net/index.php?section=Receiver

73
Thomas DM4TR


----- Original Message ----- From: "Ken"<[email protected]>
To:<[email protected]>
Sent: Thursday, September 13, 2012 10:28 AM
Subject: LF: RE: MF tonite


Hi Stefan.
What mechanical filter are you using?.
73.
Ken
M0KHW

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Stefan Schäfer
Sent: 12 September 2012 21:02
To: [email protected]
Subject: LF: MF tonite

Christian,

Are you QRV tonite? I would like to see or better hear the difference of
my RX performance when using my band filter i was testing in the
afternoon.

It is the mechanical filter which uses source followers at the input and
output, to provide a constant accurate impedance matching to keep the
passband ripple as low as possible. The afternoons tests have been very
promising, see https://dl.dropbox.com/u/19882028/MF/MF%20Filter.png
This is the frequency response:

https://dl.dropbox.com/u/19882028/MF/473%20kHz%20ZF%20Filter%2040%20dB.png

There should be a much better image rejection now and so maybe a few
more dB SNR... Unfortunately the filter does not cover the 502 kHz
region. But this problem will be gone in some months...

Will be on 472.5 kHz soon.

73, Stefan/DK7FC